JP6918591B2 - Electromagnetic wave detector and its manufacturing method - Google Patents

Description

The present invention relates to an electromagnetic wave detector that detects an electromagnetic wave and a method for manufacturing the same, and particularly absorbs an electromagnetic wave and detects it as a change in an electric current.

Graphene is one of the allotropes of carbon. Graphene is a semiconductor with no bandgap, which is a sheet-like single-layer structure in which carbon atoms are arranged and bonded in a honeycomb lattice pattern. Graphene has unique properties such as high physical strength, electron mobility, and thermal conductivity, and various applied researches are underway. In addition, graphene has a wide absorption spectrum and is being studied for use as an electromagnetic wave detector.

Patent Document 1 describes an FET-type photodetector in which a gate insulating film and graphene are laminated in this order on a substrate made of Si, and a source electrode and a drain electrode are formed on the graphene. In Patent Document 1, light is detected by a change in electrical resistance due to absorption of electromagnetic waves of graphene, and a gate voltage is applied to utilize an operating point having a large rate of change in light current.

Patent Document 2 describes an electromagnetic wave detector in which a metal layer, an insulating layer, a graphene layer, and an isolated metal are formed in this order on a substrate, and two electrodes are provided on the graphene layer so as to face each other with the isolated metal interposed therebetween. There is. The isolated metal is composed of a metal that easily causes surface plasmon resonance, and is a pattern in which a plurality of squares are arranged in a square lattice at intervals. In this electromagnetic wave detector, surface plasmon resonance occurs in an insulating layer sandwiched between a metal layer and an isolated metal, and an electromagnetic wave having a predetermined wavelength is localized. Then, since the graphene layer is arranged in the resonator, electromagnetic waves having a predetermined wavelength repeatedly enter the graphene layer. As described above, in Patent Document 2, the surface plasmon resonance and the resonator structure are used to increase the absorption rate of electromagnetic waves and improve the detection sensitivity of electromagnetic waves.

Patent Document 3 includes an electromagnetic wave detector that has a structure in which an upper metal pattern composed of a lower metal layer, an insulating layer, and graphene is formed in this order, and converts a temperature change of the structure into an electric signal to detect an electromagnetic wave. Has been described. In Patent Document 3, the light absorption rate of graphene is increased by utilizing surface plasmon resonance due to the upper metal pattern.

Special Table 2013-502735 JP-A-2015-45629 Japanese Unexamined Patent Publication No. 2015-12417

However, with the photodetector of Patent Document 1, it is difficult to detect with high sensitivity because the light absorption rate of graphene is low.

Further, in the structures of Patent Documents 1 to 3, noise and dark current cannot be reduced, so that there is a problem that device performance such as D * value is low.

Further, in Patent Documents 1 to 3, since graphene is formed on the entire surface, even if the charge induced by plasmon is biased, the bias is canceled and the detection sensitivity cannot be improved.

Therefore, an object of the present invention is to realize an electromagnetic wave detector capable of detecting electromagnetic waves with high sensitivity.

In the electromagnetic wave detector for detecting an electromagnetic wave, the semi-conductor layer, a gate electrode, a transistor structure having a source electrode and a drain electrode, provided apart from the semiconductor layer, and the absorbent layer to cause an electric field to absorb electromagnetic waves, It has an insulating film provided between the semiconductor layer and the absorption layer and set to a thickness that does not generate a tunnel current from the absorption layer to the semiconductor layer, and the semiconductor layer is two-dimensionally bonded by a strong bond. It is a substance having a layered structure in which the sheet-like structure is laminated by weak bonding, and the plane pattern of the semiconductor layer does not overlap with the plane pattern of the absorption layer and is the circumference of the absorption layer. is set to a pattern located in the vicinity of at least partially of the gate voltage of the transistor structure - drain current characteristic is changed by the semiconductor layer is exposed to an electric field generated by the absorption of the electromagnetic wave absorbing layer, that It is a characteristic electromagnetic wave detector.

In the present invention, the fact that the plane pattern of the semiconductor layer and the plane pattern of the absorption layer do not overlap does not mean that they do not completely overlap, but some overlap is allowed.

In the present invention, the layered substance refers to a substance having a layered structure and having a laminated structure of one layer to several layers.

The semiconductor layer may be any layered material, but graphene or a transition metal dichalcogenide is preferable.

The absorption layer may be any material as long as it absorbs electromagnetic waves to generate an electric field, and a material that absorbs electromagnetic waves by surface plasmon resonance or a material that generates electron-hole pairs by absorbing electromagnetic waves may be used. can.

The planar pattern of the absorption layer is preferably a pattern having symmetry of 2 times or more. Electromagnetic waves can be absorbed efficiently, and electromagnetic waves can be detected with higher sensitivity.

The planar pattern of the semiconductor layer may be any pattern as long as it does not overlap with the planar pattern of the absorption layer and is located in the vicinity of at least a part of the circumference of the absorption layer. However, if the plane pattern of the absorption layer is a periodic pattern in which two isosceles triangles are stacked at the apex angle and the bowtie-type unit structure is arranged in a square lattice, the plane pattern of the semiconductor layer is the bowtie. It should be striped along the base of the isosceles triangle of the mold. Electromagnetic waves can be detected with higher sensitivity. Further, when the plane pattern of the absorption layer is a periodic pattern in which square unit structures are arranged in a square grid pattern, it is preferable to use a striped pattern along one side of the square of the absorption layer. Electromagnetic waves can be detected with higher sensitivity. Alternatively, it is more desirable to have a grid pattern along each side of the absorption layer. Electromagnetic waves can be detected with even higher sensitivity.

The structure may be such that the absorption layer and the semiconductor layer are formed on the same surface, or the absorption layer and the gate electrode are formed on the same surface. The manufacturing process can be reduced and the cost can be reduced.

Further, two or more gate electrodes may be provided. The electrical characteristics of the transistor can be controlled more finely, and electromagnetic waves can be detected with higher sensitivity.

The electromagnetic wave detector of the present invention generates an electric field around the absorption layer by absorbing the electromagnetic wave by the absorption layer, and exposes the semiconductor layer to a region where the generated electric field is strong to change the electrical characteristics of the semiconductor layer. It is generated and the electromagnetic wave is detected by the change.

As described above, in the electromagnetic wave detector of the present invention, the structure responsible for absorbing the electromagnetic wave and the structure for detecting the current change accompanying the absorption of the electromagnetic wave are separated, so that the influence of noise and dark current is avoided. It is possible to detect electromagnetic waves with high sensitivity.

The figure which showed the structure of the electromagnetic wave detector of Example 1. FIG. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the structure of the electromagnetic wave detector of the modification. The figure which showed the manufacturing process of the electromagnetic wave detector of Example 1. FIG. The graph which showed the gate voltage-drain current characteristic of the transistor which uses graphene as a channel. The figure which showed the change of the gate voltage-drain current characteristic of the transistor which uses graphene as a channel. The figure which showed the plane pattern of the semiconductor layer 12 and the absorption layer 14. The graph which showed the transmission spectrum of the absorption layer 14. The figure which showed the plane pattern of the semiconductor layer 12 and the absorption layer 14. The graph which showed the transmission spectrum of the absorption layer 14. The figure which showed the electric field strength distribution when the absorption layer 14 has a bowtie shape. The figure which showed the electric field strength distribution when the absorption layer 14 is a square. The graph which showed the transmission spectrum of the absorption layer 14. The figure which showed the electric field strength distribution when the absorption layer 14 has a bowtie shape. The figure which showed the electric field strength distribution when the absorption layer 14 is a square. The figure which showed the plane pattern of the semiconductor layer 12 and the absorption layer 14.

Specific examples of the present invention will be described below, but the present invention is not limited to the examples.

FIG. 1 is a diagram showing a configuration of an electromagnetic wave detector according to the first embodiment. As shown in FIG. 1, the electromagnetic wave detector of the first embodiment includes a substrate 10, a first insulating film 11 provided on the substrate 10, a semiconductor layer 12 provided on the first insulating film 11, and a semiconductor layer. The second insulating film 13 provided on the 12 and the absorbing layer 14 provided on the second insulating film 13, the third insulating film 18 covering the absorbing layer 14, the gate electrode 15, the source electrode 16, and the drain electrode. 17 and. The substrate 10, the first insulating film 11, the semiconductor layer 12, the gate electrode 15, the source electrode 16, and the drain electrode 17 correspond to the transistor structure (MOSFET) of the present invention. The electromagnetic wave detector of the first embodiment is a FET type electromagnetic wave detector that detects far infrared rays by a change in drain current using the semiconductor layer 12 as a channel.

(About substrate 10)
The substrate 10 is made of n—Si having a first insulating film 11 formed on its surface. The first insulating film 11 is a Si thermal oxide film (SiO ₂ ) and has a thickness of 500 nm. The first insulating film 11 functions as a gate insulating film of the FET.

The substrate 10 is not limited to Si, and any material can be used. However, when detecting far infrared rays from the back surface side of the substrate 10, the substrate 10 needs to be made of a material that transmits far infrared rays. When the substrate 10 is made of a far-infrared ray transmitting material, both far-infrared rays from both the front surface side and the back surface side of the substrate 10 may be detected.

Further, although the first insulating film 11 is a thermal oxide film of Si, SiO ₂ formed by another method may be used, or an insulator other than SiO _{2 may be used.} For example, Al ₂ O ₃ , SiN, SiON, TiO ₂ , HfO ₂ ZrO ₂ , Ta ₂ O _{5, and the} like can be used. Further, different materials may be laminated.

Further, in the electromagnetic wave detector of the first embodiment, since the substrate 10 is a bottom gate type, the substrate 10 is used as a conductive material, but when the top gate type is used, an insulating material may be used.

(About semiconductor layer 12)
The semiconductor layer 12 is made of graphene and is located in contact with the first insulating film 11. Here, graphene includes not only a single layer but also several layers, for example, 1 to 9 layers. The semiconductor layer 12 is a layer that operates as a channel of a transistor. The semiconductor layer 12 is formed in a pattern that does not overlap with the planar pattern of the absorption layer 14 and is located in the vicinity of at least a part of the circumference of the absorption layer 14. The details of the pattern will be described later.

As the semiconductor layer 12, a semiconductor of a layered substance other than the graphene layer can also be used. Here, the layered substance has a layered structure in which a sheet-like structure two-dimensionally bonded by a strong bond is used as a unit, and the sheet-like structure is laminated by a weak bond, and the number of layers is about one layer to several layers (for example). It is assumed that a laminated product of 1 to 9 layers) is shown.

For example, transition metal dichalcogenides can be used. The transition metal dichalcogenide is a layered material represented by the _{chemical formula MX 2.} Here, M is a transition metal, for example, Mo, W, Ta, Hf, Sn, Ti, Re, Sn, and the like. Further, X is S, Se, or Te. Specifically, MoS ₂ , WS ₂ , WSe ₂ , MoSe ₂ , HfS ₂ , SnS _{2 and the} like can be used.

Further, for example, a group 13 chalcogenide or a group 14 chalcogenide can be used. Group 13 chalcogenides are compounds of Group 13 and Group 16 elements, and Group 14 chalcogenides are compounds of Group 14 and Group 16 elements. Specifically, GaS, GaSe, InSe, GeSe, SnSe _{2 and the} like can be used.

Further, for example, a layered substance composed of a single element such as phosphorene, silicene, and germanene can be used.

(About the second insulating film 13)
The second insulating film 13 is provided in contact with the semiconductor layer 12. The second insulating film 13 is made of SiO ₂ . The second insulating film 13 is provided to separate the semiconductor layer 12 and the absorption layer 14 so that a current does not leak from the absorption layer 14 to the semiconductor layer 12.

The thickness of the second insulating film 13 may be set so that current does not leak from the absorption layer 14 to the semiconductor layer 12 due to the tunnel effect. This is because if there is a current leak, the detection accuracy will be affected. It is not necessary for the thickness to completely prevent current leakage, and it is permissible for some current leakage to occur within a range that does not affect the detection accuracy of far infrared rays.

For example, the thickness of the second insulating film 13 is preferably 2 nm or more. If the thickness is less than 2 nm, the current leakage cannot be sufficiently suppressed. The thickness of the second insulating film 13 is preferably 100 nm or less. This is because when the distance between the absorption layer 14 and the semiconductor layer 12 is increased, the electric field strength of the electric field generated in the absorption layer 14 in the semiconductor layer 12 becomes weak, and the detection accuracy of far infrared rays is not sufficiently improved. Further, if the second insulating film 13 becomes thick, it takes time and cost to manufacture, and the electromagnetic wave detector also becomes large. The more desirable thickness of the second insulating film 13 is 2 to 50 nm, and more preferably 5 to 20 nm.

Further, the material of the second insulating film 13 is _{not limited to SiO 2} , and may be a material different from that of the first insulating film 11. For example, Al ₂ O ₃ , SiN, SiON, TiO ₂ , HfO ₂ ZrO ₂ , Ta ₂ O _{5, and the} like can be used. The second insulating film 13 may be a laminate of a plurality of materials. A high dielectric constant material is desirable for the second insulating film 13 in order to effectively prevent current leakage while reducing the size of the device. For example, a material having a relative permittivity of 4 or more is desirable.

(About absorption layer 14)
The absorption layer 14 is provided in a partial region on the second insulating film 13. The absorption layer 14 has a structure in which Cr having a thickness of 5 nm and Au having a thickness of 30 nm are laminated in this order. The Au layer is a layer for absorbing far infrared rays having a desired wavelength by surface plasmon resonance and generating an electric field around the absorption layer 14. The Cr layer is a layer for enhancing the adhesion between the second insulating film 13 and the Au layer. The planar pattern of the absorption layer 14 is formed into a pattern capable of efficiently absorbing a desired wavelength. The details of the pattern will be described later.

The thickness of the absorption layer 14 is not limited to 30 nm, and is arbitrary as long as it can sufficiently absorb far infrared rays having a desired wavelength. For example, the range of 10 to 1000 nm is sufficient.

The material of the absorption layer 14 is not limited to Au, and any material can be used as long as it absorbs far infrared rays to generate an electric field, and it may be an insulator, a metal, a semiconductor, or an inorganic material. It may be an organic material. It may be a laminate of a plurality of materials. Further, the absorption of far infrared rays may be due to lattice defects or impurities in the material. Further, the electric field generation factor may be any factor such as one due to surface plasmon resonance, one due to the localization of electric charge due to the generation of electron-hole pairs, and one due to polarization.

For example, a material that produces surface plasmon resonance. Any such material may be a metal, a semiconductor, or an insulator. Examples of such materials are, in addition to Au of Example 1, metals such as Ag and Cu _{, ferroelectrics such as PbTiO 3} and BaTiO ₃ , and transition metal dichalcogenides. For the transition metal dichalcogenide, the materials mentioned in the description of the semiconductor layer 12 can be used.

Further, for example, it is a material in which electron-hole pairs are generated by absorption of electromagnetic waves, and an electric field is generated by the localization of the electrons and holes. For example, a pyroelectric body Ge, Si, GaAs, GaN, a semiconductor such as AlGaAs, an organic dye, an organic semiconductor such as phthalocyanine-based material, a ferroelectric material such as BaTiO _3, etc. PbTiO _3. Further, it may be a pn junction structure or a pin junction structure. The localization of electrons and holes becomes more prominent, and a stronger electric field is generated, so that the far-infrared detection accuracy of the electromagnetic wave detector can be improved.

In the first embodiment, the positional relationship between the semiconductor layer 12 and the absorption layer 14 is in the order of the absorption layer 14 and the semiconductor layer 12 in order from the far-infrared ray incident side (the surface side of the substrate 10), but conversely, the semiconductor layer. The structure may be in the order of 12 and the absorption layer 14. As an example, FIG. 2 shows a configuration in which the absorption layer 14 on the second insulating film 13 is embedded in the first insulating film 11 (referred to as an absorption layer 14A) in the first embodiment, and the second insulating film 13 is omitted. Is shown. Even with the configuration as shown in FIG. 2, since the far infrared rays transmitted through the semiconductor layer 12 can be absorbed by the absorption layer 14A, it can be operated in the same manner as the electromagnetic wave detector of the first embodiment.

Further, in the first embodiment, the absorption layer 14 is only one layer, but two or more layers may be provided. This makes it possible to detect a plurality of wavelengths. As an example, FIG. 3 shows a configuration in which an absorption layer 14A is further added to the first insulating film 11 in the first embodiment. In the electromagnetic wave detector of FIG. 3, the absorption wavelength of the absorption layer 14 and the absorption wavelength of the absorption layer 14A can be changed by changing the material and plane pattern of the absorption layer 14 and the material and plane pattern of the absorption layer 14A. good. For example, it is possible to realize an electromagnetic wave detector capable of detecting both far infrared rays having a wavelength of 5 μm and far infrared rays having a wavelength of 10 μm.

(About the third insulating film 18)
The third insulating film 18 is formed so as to cover the absorption layer 14. The thickness of the third insulating film 18 is, for example, 5 to 20 nm. The absorbing layer 14 is in a state of being internally sealed by the second insulating film 13 and the third insulating film 18. By sealing the absorption layer 14 with the insulating film in this way, the absorption layer 14 is physically and chemically protected. The third insulating film 18 is made of SiO ₂ . In _{addition to SiO 2} , any material that can physically and chemically protect the absorption layer 14 can be used.

(About electrode structure)
A contact hole is provided in a part of the second insulating film 13 and the third insulating film 18, and the semiconductor layer 12 is exposed on the bottom surface thereof. A source electrode 16 and a drain electrode 17 are provided in contact with the exposed semiconductor layer 12. The source electrode 16 and the drain electrode 17 are provided at a predetermined distance from each other. The gate electrode 15 is provided in contact with the back surface of the substrate 10. The source electrode 16, the drain electrode 17, and the gate electrode 15 are made of Ti / Au.

In the first embodiment, the gate electrode 15 constitutes an FET (MOSFET) having an insulated gate structure connected to the semiconductor layer 12 via the first insulating film 11, but a Schottky on graphene is used as the material of the gate electrode 15. Using a material to be connected, the gate electrode 15 and the semiconductor layer 12 may be directly connected to form a Schottky gate structure FET (MESFET). For example, the substrate 10 may be used as a material for Schottky connection to graphene, and may also have a structure that also serves as a gate electrode 15.

Further, in the first embodiment, one gate electrode 15 is provided, but a plurality of gate electrodes 15 may be provided. By providing the plurality of gate electrodes 15, the position where the voltage is applied to the semiconductor layer 12 can be controlled, the operation of the FET can be changed from bipolar to semipolar, and the shift amount of the Dirac point of the semiconductor layer 12 can be controlled more easily. It is possible to improve the detection accuracy of electromagnetic waves. Further, in the first embodiment, the back gate type structure in which the gate electrode 15 is provided on the back surface side of the substrate 10 is used, but a top gate type structure in which the gate electrode 15 is provided on the front surface side of the substrate 10 may be used, or the front surface side may be used. A dual gate type structure may be provided on both the back side and the back side.

Some specific examples of the case where a plurality of gate electrodes 15 are provided will be illustrated below. The electromagnetic wave detector of FIG. 4 has a configuration in which a gate electrode 15A made of graphene is further added on the third insulating film 18 in the first embodiment. In this case, the third insulating film 18 also functions as a gate insulating film.

Further, the electromagnetic wave detector of FIG. 5 has a configuration in which gate electrodes 25 and 26 are added instead of the gate electrode 15, and in the first embodiment, the substrate 10 is replaced with a high-resistance n—Si that transmits far infrared rays. A substrate 20 made of the material is used. A gate electrode 25 made of graphene, a first insulating film 11, and a semiconductor layer 12 are laminated in this order on the substrate 20, and on the semiconductor layer 12, the second insulating film 13, the absorbing layer 14, and the like are the same as in the first embodiment. A source electrode 16, a drain electrode 17, and a third insulating film 18 are provided. Further, a gate electrode 26 made of Ti / Au is provided on the third insulating film 18. On the back surface of the substrate 20, a contact hole for exposing the gate electrode 25 to the bottom surface is provided, and a contact electrode 27 for filling the contact hole and connecting to the gate electrode 25 is provided. In the electromagnetic wave detector of FIG. 5, far infrared rays transmitted through the substrate 20 and incident from the back surface side of the substrate 20 are detected.

Further, the gate electrode 15 may be provided on the same surface as the absorption layer 14. An example is shown in FIG. In the electromagnetic wave detector of FIG. 6, the semiconductor layer 12 and the second insulating film 13 are formed in this order on the high-resistance substrate 20, and the absorption layer 14 and the gate electrode 15 are formed on the second insulating film 13 at a distance from each other. Further, a contact hole is provided in the second insulating film 13 to form a source electrode 16 and a drain electrode 17 to be connected to the semiconductor layer 12. When the absorption layer 14 and the gate electrode 15 are provided on the same surface in this way, the element structure can be simplified, the number of times the insulating film is formed can be reduced, and the manufacturing cost can be reduced. Further, the second insulating film 13 for suppressing the current leakage by separating the absorption layer 14 and the semiconductor layer 12 can also function as a gate insulating film.

Further, in the first embodiment, the absorption layer 14 and the semiconductor layer 12 are located on different surfaces, but if they are provided apart from the absorption layer 14 by an insulating film so as not to cause a current leak to the semiconductor layer 12. , The positional relationship between the absorption layer 14 and the semiconductor layer 12 may be arbitrary. The absorption layer 14 and the semiconductor layer 12 may be provided on the same surface. The area where the insulating film is formed can be reduced, the manufacturing process can be simplified, and the cost can be reduced. When the absorption layer 14 and the semiconductor layer 12 are formed on the same plane, the plane pattern of the absorption layer 14 and the plane pattern of the semiconductor layer 12 do not necessarily overlap.

Some specific examples of the case where the absorption layer 14 and the semiconductor layer 12 are formed on the same surface will be illustrated below. 7A and 7B show a configuration of an electromagnetic wave detector of a modified example, FIG. 7A is a cross-sectional view, and FIG. 7B is a plan view. As shown in FIG. 7, the first insulating film 11 is provided on the substrate 10, the absorption layer 14 having a square pattern is provided on the first insulating film 11, and the semiconductor layer 12 is also provided on the first insulating film 11. Has been done. A square window is opened in the semiconductor layer 12, and the absorption layer 14 is located in the window at a certain distance from the semiconductor layer 12. A third insulating film 18 is provided so as to cover the absorption layer 14 and the semiconductor layer 12, and the third insulating film 18 is also located in the gap between the absorption layer 14 and the semiconductor layer 12. The gate electrode 15, the source electrode 16, and the drain electrode 17 are provided in the same manner as in the first embodiment.

FIG. 8 shows a configuration in which the electromagnetic wave detector of FIG. 7 is provided with a gate electrode 15A on the third insulating film 18 in the same manner as in FIG. 4, and has two gate electrodes.

FIG. 9 shows the electromagnetic wave detector of FIG. 7 in which two gate electrodes 25 and 26 are provided in the same manner as in FIG.

Since it is not necessary to provide the second insulating film 13 in these electromagnetic wave detectors of FIGS. 7 to 9 as compared with the electromagnetic wave detector of the first embodiment, the manufacturing process can be further reduced and the cost can be reduced.

(Manufacturing method of electromagnetic wave detector of Example 1)
Next, the method of manufacturing the electromagnetic wave detector of the first embodiment will be described with reference to FIG.

First, the semiconductor layer 12 is formed on the copper foil by using the CVD method. A carbon-containing gas such as methane or ethane is used as the carbon source. The temperature is, for example, 1000 ° C. or higher, and the pressure is, for example, 500 Pa or lower.

Next, a low-resistance substrate 10 made of n—Si having a 500 nm thermal oxide film (first insulating film 11) formed on the front surface and the back surface is prepared. A semiconductor layer 12 on a copper foil is attached to the surface of the substrate 10. Then, the copper foil is removed by wet etching. In this way, the semiconductor layer 12 is transferred onto the first insulating film 11 on the surface of the substrate 10 (see FIG. 10A).

The method of forming the semiconductor layer 12 is not limited to the CVD method, and any method such as a tape peeling method may be used.

Next, a semiconductor layer 12 having a predetermined pattern is formed on the first insulating film 11 by photolithography and dry etching (see FIG. 10B).

Next, a second insulating film 13 having a thickness of 20 nm is formed on the semiconductor layer 12 by a CVD method, and an absorption layer 14 having a predetermined pattern is formed on the second insulating film 13 (see FIG. 10C). .. The absorption layer 14 is Cr / Au, the Cr layer is 5 nm, and the Au layer is 30 nm. The absorption layer 14 is formed by a sputtering method, a vapor deposition method, or the like. Photolithography and dry etching are used for patterning the absorption layer 14. Alternatively, patterning may be performed by a lift-off method.

Next, the third insulating film 18 is formed by the CVD method so as to cover the absorption layer 14. Then, a part of the second insulating film 13 and the third insulating film 18 is dry-etched to form a contact hole, and the semiconductor layer 12 is exposed on the bottom surface of the contact hole. Then, the source electrode 16 and the drain electrode 17 are formed on the exposed semiconductor layer 12 by photolithography, thin film deposition, and lift-off (see FIG. 10D). Next, the thermal oxide film on the back surface of the substrate 10 is removed to form the gate electrode 15. As described above, the electromagnetic wave detector of Example 1 shown in FIG. 1 is manufactured.

(About the operation of the electromagnetic wave detector)
Next, the operation of the electromagnetic wave detector of the first embodiment will be described.

First, a predetermined voltage is applied to the gate electrode 15 and set so as to be a region in which the drain current changes significantly with respect to a change in the drain voltage. The transistor having the semiconductor layer 12 made of graphene as a channel shows both polarities, and as shown in FIG. 11, the curve of the gate voltage-drain current characteristic appears line-symmetrically. Therefore, the gate voltage is applied so as to be in the region A or the region B where the slope of the curve is large.

When far-infrared rays are incident from the surface side of the substrate 10 of the electromagnetic wave detector of the first embodiment while the gate voltage is applied in this way, the far-infrared rays are absorbed by the absorption layer 14. Then, the distribution of electrons in the absorption layer 14 is biased, and an electric field is generated around the absorption layer 14.

When the semiconductor layer 12 is exposed to the electric field generated by the absorption of far infrared rays of the absorption layer 14 and a voltage is applied, the Dirac point of graphene constituting the semiconductor layer 12 shifts. Since the semiconductor layer 12 has a planar pattern as described later, the semiconductor layer 12 can be efficiently exposed to a region having a strong electric field strength in the electric field generated by the absorption of far infrared rays of the absorption layer 14. As a result, the Dirac point of the semiconductor layer 12 can be efficiently shifted. Due to the shift of the Dirac point, the electrical characteristics (characteristics of gate voltage-drain current) of the transistor having the semiconductor layer 12 as a channel also change, and the curve shifts as shown in FIG.

Here, it is set in advance in a region (region A or region B in FIG. 11) in which the drain current changes significantly due to fluctuations in the gate voltage due to the application of the gate voltage. Therefore, the drain current also changes significantly due to the change in the electrical characteristics of the transistor using graphene as a channel (see FIG. 12). Far infrared rays can be detected by this change in drain current. In addition, the intensity of far infrared rays can be measured from the amount of change in the drain current.

In the electromagnetic wave detector of the first embodiment, the function of absorbing far infrared rays and the function of a transistor that detects the absorption as a change in current are separated. Further, the semiconductor layer 12 is arranged in a region where the electric field generated by absorption of far infrared rays is strong, and is not arranged in a region where the electric field is weak. Therefore, the electromagnetic wave detector of the first embodiment is resistant to noise and dark current, can detect far infrared rays with high sensitivity, and can improve the specific detection ability (D *), for example.

(Pattern of absorption layer 14 and semiconductor layer 12)
As described above, the planar patterns of the absorption layer 14 and the semiconductor layer 12 are set so that far infrared rays can be detected efficiently. The plane pattern will be described in detail with reference to the figure.

First, the plane pattern of the absorption layer 14 will be described. As shown in FIG. 13, the absorption layer 14 is a pattern in which a bowtie-shaped shape is used as a unit structure and the unit structures are arranged in a square lattice pattern. The bowtie-shaped shape is a shape in which the apex angles of two isosceles triangles are opposed to each other so as to partially overlap. Further, the two bases 14a of the bowtie type are arranged so as to be perpendicular to the polarization direction to be detected. As a result, far infrared rays in the polarization direction can be detected with high efficiency.

FIG. 14 is a graph showing the results of calculating the transmission spectrum of the absorption layer 14 by simulation. The shape of the bow tie type of the absorption layer 14 is such that the length of the base 14a of the two isosceles triangles is 2340 nm, the overlapping width of the apex angles is 80 nm, the distance between the two bases 14a is 2340 nm, and the shape of the bow tie type has a period of 2590 nm. The plane pattern was infinitely arranged in a square grid pattern. Further, the far infrared rays were incident in the thickness direction of the absorption layer 14, and the polarization direction was set to be orthogonal to the bottom 14a of the bowtie type. As shown in FIG. 14, the absorption layer 14 having such a plane pattern has a transmittance of far infrared rays having a wavelength of 10 μm of about 0.02, and it can be seen that the absorption layer 14 having a wavelength of 10 μm can efficiently absorb far infrared rays.

The unit structure of the absorption layer 14 is a bowtie type structure in the first embodiment, but any pattern may be used. However, in order to efficiently absorb far infrared rays, it is preferable to use a pattern having symmetry of twice or more. For example, it may be a pattern such as an equilateral triangle, a square, a rectangle, a regular hexagon, a circle, an ellipse, or a cross. In particular, if the symmetry is 4 times or more, it can be efficiently detected even if it is unpolarized.

As another example of the unit structure of the absorption layer 14, FIG. 15 shows a plane pattern when the unit structure of the absorption layer 14 is a square. Further, FIG. 16 is a graph showing the result of calculating the transmission spectrum of the absorption layer 14 in this plane pattern by simulation. The length of one side of the square was 2 μm, and the squares were arranged infinitely in a square grid with a period of 5 μm to form a plane pattern. The thickness of the absorption layer 14 was 100 nm. As shown in FIG. 16, the transmittance of far infrared rays having a wavelength of 5 μm is about 0.07, and it can be seen that far infrared rays having a wavelength of 5 μm can be efficiently absorbed.

Further, in the first embodiment, the absorption layer 14 has a pattern in which the unit structures are arranged in a square grid pattern, but the arrangement pattern and the number of arrangements may be set according to a desired absorption wavelength, absorption bandwidth, and the like. In addition to the lattice, a periodic pattern such as a triangular lattice or a honeycomb lattice may be used. However, it is desirable that the absorption layer 14 as a whole is arranged so as to have a symmetry of 2 times or more. The absorption layer 14 can efficiently absorb far infrared rays. Further, it may have only one unit structure instead of a pattern in which a plurality of unit structures are arranged.

Next, the planar pattern of the semiconductor layer 12 when the unit structure of the absorption layer 14 has a bowtie shape will be described. As shown in FIG. 13, the semiconductor layer 12 is formed in a striped shape. Assuming that the direction perpendicular to the base 14a in the bowtie shape of the absorption layer 14 is the x-axis direction and the direction along the bottom 14a is the y-axis direction, the direction of the stripe is the y-axis direction. Further, it is provided at a position of a gap between one base 14a and the other bottom 14a of an adjacent bowtie-shaped shape, and the absorption layer 14 and the semiconductor layer 12 are set so as not to overlap in a plan view. Further, the width of the stripe is equal to the distance between one base 14a and the other base 14a of the adjacent bowtie shape.

FIG. 17 is a diagram showing the results of simulating the intensity distribution of the electric field generated by absorption by the absorption layer 14 of far infrared rays having a wavelength of 10 μm polarized in the x-axis direction. It is the electric field strength distribution in the xy plane just below the absorption layer 14. When the absorption layer 14 has a bowtie shape, the electric field strength distribution becomes very weak in the region where the absorption layer 14 and the absorption layer 14 overlap in a plan view, as shown in FIG. On the other hand, in the region near the bottom 14a of the bowtie shape, a strong negative electric field strength is exhibited.

Therefore, by forming the semiconductor layer 12 into a stripe shape shown in FIG. 13, the semiconductor layer 12 is arranged in a region where the electric field generated by absorption of far infrared rays is strong (a region near the bottom 14a of the bowtie shape), and the electric field is weak. The semiconductor layer 12 is not arranged in the region (the region overlapping the absorption layer 14). By arranging the semiconductor layer 12 in this way, the Dirac points of graphene constituting the semiconductor layer 12 can be efficiently shifted, and far infrared rays can be detected with high sensitivity.

Next, the planar pattern of the semiconductor layer 12 when the unit structure of the absorption layer 14 is square will be described. The semiconductor layer 12 is formed in a striped shape as shown in FIG. Of the square sides of the absorption layer 14, the direction along one side is the x-axis direction, the direction perpendicular to this is the y-axis direction, and the stripe direction is the y-axis direction. Further, it is provided in a region between the squares, and the absorption layer 14 and the semiconductor layer 12 are set so as not to overlap in a plan view. Also, the width of the stripe is equal to the distance between the squares.

FIG. 18 is a diagram showing the results of simulating the intensity distribution of the electric field generated by absorption by the absorption layer 14 of far infrared rays having a wavelength of 5 μm polarized in the x-axis direction. It is an electric field strength distribution in the xy plane immediately below the absorption layer 14. As shown in FIG. 18, the electric field strength distribution becomes very weak in the region overlapping the absorption layer 14. On the other hand, among the sides of the square, the region near the side orthogonal to the x-axis direction shows a strong negative electric field strength, and the region near the other side shows a weak electric field strength.

Therefore, by forming the semiconductor layer 12 into a stripe shape as shown in FIG. 15, the semiconductor layer 12 is formed in a region where the electric field generated by absorption of far infrared rays is strong (a region of the square side near the side orthogonal to the x-axis direction). Is arranged so that the semiconductor layer 12 is not arranged in the region where the electric field is weak (the region overlapping the absorption layer 14). By arranging the semiconductor layer 12 in this way, the Dirac points of graphene constituting the semiconductor layer 12 can be efficiently shifted, and far infrared rays can be detected with high sensitivity.

The plane pattern of the semiconductor layer 12 when detecting polarized far infrared rays in the x-axis direction has been described above, but the plane pattern of the semiconductor layer 12 when detecting unpolarized far infrared rays will be described.

First, consider the case where the unit structure of the absorption layer 14 has a bowtie shape. When unpolarized far-infrared rays are incident on the absorption layer 14 having a bowtie-shaped unit structure, far-infrared rays having a wavelength of 10 μm are not absorbed so much with respect to polarized light in the y-axis direction, as shown in FIG. Although it cannot be done, far infrared rays having a wavelength of 10 μm can be efficiently absorbed for polarized light in the x-axis direction as shown in FIG.

FIG. 20 is a graph showing the intensity distribution of the electric field generated when unpolarized far infrared rays are absorbed. As shown in FIG. 20, even in the case of unpolarized far-infrared rays, the electric field strength is negative in the region near the bottom 14a of the bowtie shape, and the electric field strength is very weak in the region overlapping the absorption layer 14.

Therefore, if the planar pattern of the semiconductor layer 12 is a striped pattern as in FIG. 13, far infrared rays can be detected with high sensitivity even in the case of non-polarized light.

Next, consider the case where the unit structure of the absorption layer 14 is square. Due to the symmetry of the shape of the absorption layer 14 having a square unit structure, the polarization in the x-axis direction and the polarization in the y-axis direction have the same transmission spectrum (see FIG. 16), and the wavelength is efficiently arranged even if it is unpolarized. It can absorb far infrared rays of 5 μm.

Further, FIG. 21 is a diagram showing an electric field strength distribution when unpolarized far infrared rays are incident when the unit structure of the absorption layer 14 is a square. As shown in FIG. 21, the electric field strength is weak in the region overlapping with the absorption layer 14, while the electric field strength is negative in the region near each side of the square. When far-infrared light polarized in the x-axis direction was incident, only the vicinity of the side orthogonal to the x-axis showed a strong negative electric field strength, but in the case of unpolarized light, it was negative in the vicinity of all sides. Shows the strong electric field strength of.

Therefore, when the unit structure of the absorption layer 14 is square, unpolarized far-infrared rays can be detected with high sensitivity even in the same striped shape as in FIG. Polarized far infrared rays can be detected. FIG. 22 shows a plane pattern when the semiconductor layer 12 is formed into a grid pattern. As shown in FIG. 22, the planar pattern of the semiconductor layer 12 includes a stripe extending in the x-axis direction in the region between the squares of the absorption layer 14 and a stripe extending in the y-axis direction in the region between the squares. Is a grid-like pattern in which is orthogonally intersected. By forming such a grid pattern, the semiconductor layer 12 is arranged in a region where the electric field is strong (a region near each side of the square) generated by absorption of far infrared rays, and a region where the electric field is weak (absorption layer 14). The semiconductor layer 12 is not arranged in the overlapping region).

From the above examination, if the planar pattern of the semiconductor layer 12 is not provided in the region overlapping the planar pattern of the absorption layer 14, and the pattern is located in the vicinity of at least a part of the circumference of the absorption layer 14. It can be seen that the semiconductor layer 12 can be exposed to a region where the electric field strength is strong in the electric field generated by the absorption of far infrared rays, and far infrared rays can be detected efficiently. In particular, the shape of the circumference of the unit structure of the absorption layer 14 is a shape having a set of parallel opposite sides and a set of opposite sides orthogonal to it (for example, a square, a rectangle, an octagon, etc.), and the semiconductor layer 12 has a shape. If the plane pattern is a grid pattern along those sides, unpolarized far infrared rays can be detected with high sensitivity.

It is not necessary to prevent the patterns of the absorption layer 14 and the semiconductor layer 12 from completely overlapping, and there may be some overlap. However, it is desirable that the width of the overlap between the absorption layer 14 and the semiconductor layer 12 is 200 nm or less in a plan view. It is more preferably 100 nm or less, and even more preferably 20 nm or less. The most desirable thing is to avoid overlapping. Further, if the pattern between the absorption layer 14 and the semiconductor layer 12 is too far apart, the voltage related to the semiconductor layer 12 becomes weak when an electric field is generated in the absorption layer 14 due to the absorption of far infrared rays, and the detection sensitivity of far infrared rays becomes low. become worse. Therefore, it is desirable that the distance between the absorption layer 14 and the semiconductor layer 12 is 100 nm or less in a plan view. It is more preferably 50 nm or less, and even more preferably 20 nm or less.

Further, although the electromagnetic wave detector of Example 1 was used for detecting far infrared rays, the electromagnetic wave detector of the present invention can be used for detecting electromagnetic waves of any wavelength. For example, it can be used to detect ultraviolet rays, visible light, infrared rays, and terahertz waves. In particular, it is effective for detecting infrared rays (particularly mid-infrared rays and far-infrared rays). This is because there has not been a detector capable of detecting the mid-infrared to far-infrared region with high sensitivity.

The electromagnetic wave detector of the present invention can be used for detecting electromagnetic waves of various wavelengths.

10: Substrate 11: First insulating film 12: Semiconductor layer 13: Second insulating film 14: Absorption layer 15: Gate electrode 16: Source electrode 17: Drain electrode 18: Third insulating film

Claims (12)

In an electromagnetic wave detector that detects electromagnetic waves,
Semi conductor layer, and a transistor structure having a gate electrode, a source electrode and a drain electrode,
An absorption layer that is provided apart from the semiconductor layer and absorbs electromagnetic waves to generate an electric field.
An insulating film provided between the semiconductor layer and the absorption layer and set to a thickness that does not generate a tunnel current from the absorption layer to the semiconductor layer.
Have,
The semiconductor layer is a substance having a layered structure in which a sheet-like structure two-dimensionally bonded by a strong bond is used as a unit and the sheet-like structure is laminated by a weak bond.
The plane pattern of the semiconductor layer, the not overlap the plane pattern of the absorbent layer, and it is set to pattern positioned on at least a portion near the peripheral of the absorbent layer,
The gate voltage-drain current characteristic of the transistor structure changes when the semiconductor layer is exposed to an electric field generated by absorption of electromagnetic waves in the absorption layer.
An electromagnetic wave detector characterized by this. The plane pattern of the absorption layer is a pattern having symmetry of two times or more.
The electromagnetic wave detector according to claim 1. The plane pattern of the absorption layer is a periodic pattern in which two isosceles triangles are stacked at an apex angle and a bowtie-shaped unit structure is arranged in a square lattice pattern.
The planar pattern of the semiconductor layer is a stripe shape along the base of a bowtie-shaped isosceles triangle.
The electromagnetic wave detector according to claim 2, wherein the electromagnetic wave detector is characterized by the above. The planar pattern of the absorption layer is a periodic pattern in which square unit structures are arranged in a square grid pattern.
The planar pattern of the semiconductor layer is a striped pattern along one side of the square of the absorption layer.
The electromagnetic wave detector according to claim 2, wherein the electromagnetic wave detector is characterized by the above. The planar pattern of the absorption layer is a periodic pattern in which square unit structures are arranged in a square grid pattern.
The planar pattern of the semiconductor layer is a grid-like pattern along each side of the absorption layer.
The electromagnetic wave detector according to claim 2, wherein the electromagnetic wave detector is characterized by the above. The electromagnetic wave detector according to any one of claims 1 to 5, wherein the absorption layer and the semiconductor layer are formed on the same surface. The electromagnetic wave detector according to any one of claims 1 to 5, wherein the absorption layer and the gate electrode are formed on the same surface. The electromagnetic wave detector according to any one of claims 1 to 7, wherein the transistor structure includes two or more gate electrodes. The electromagnetic wave detector according to any one of claims 1 to 8, wherein the semiconductor layer is made of graphene. The electromagnetic wave detector according to any one of claims 1 to 8, wherein the semiconductor layer is made of a transition metal dichalcogenide. The electromagnetic wave detector according to any one of claims 1 to 10, wherein the absorption layer is made of a material that absorbs electromagnetic waves by surface plasmon resonance. The electromagnetic wave detector according to any one of claims 1 to 10, wherein the absorption layer is made of a material in which electron-hole pairs are generated by absorption of electromagnetic waves.

Images