JP3675223B2 - Avalanche photodiode and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-receiving element for optical communication, and more particularly to a structure of an avalanche photodiode (APD) that is easy to manufacture and excellent in dark current characteristics and reliability, and a manufacturing method thereof.
[0002]
[Prior art]
The three major elements constituting optical fiber communication include a light source, an optical fiber as a transmission medium, and a photodetector that detects an optical signal. Among these, the semiconductor light-receiving element is used for the light monitor of the light source and the detector of the optical signal by taking advantage of the small size, light weight and high sensitivity. As a semiconductor light-receiving element for this purpose, as a detector for a wavelength band of 0.8 μm, a PIN photodiode using Si material (hereinafter abbreviated as PD), or a high reverse bias for utilizing a high electric field An avalanche photodiode (APD) that requires a voltage but has a higher sensitivity than a PD has been developed because it has a function of amplifying a photoelectrically converted signal inside the element.
[0003]
Along with the reduction in transmission loss of optical fibers, PDs or APDs using Ge materials have been developed as light-receiving elements for so-called long wavelength bands, but Ge materials have a large dark current as photodetectors, and optical fibers There is a problem that the photoelectric conversion efficiency is extremely lowered as a material with respect to 1.55 μm light having an extremely low loss wavelength. An InGaAsP material lattice-matched to an InP substrate as a semiconductor light-receiving element that replaces this Ge material, in particular, the longest wavelength edge composition of this system. _0.53 Ga _0.47 PIN-PD or APD using an As (hereinafter referred to as InGaAs) material as a light absorption layer has been researched and developed.
[0004]
Currently, PIN-PD or APD using this InGaAs material is used as a photodetector for 1.3 μm or 1.55 μm, which is the central wavelength of optical communication. In these semiconductor light receiving elements, a light receiving region is provided on a semiconductor main surface by selectively applying impurity species by a technique such as diffusion to form a pn junction. In this structure, there are many so-called planar structures in which light is normally incident on the main surface of the semiconductor, and this is widely adopted and manufactured as an excellent structure in terms of reliability, production yield, and the like.
[0005]
On the other hand, recently, elemental technologies necessary for optical communication including various optical devices are steadily progressing. However, the demand for transmitting a large amount of information at a low price is increasing dramatically,・ Technology that can provide high-speed photo detectors at low cost is required.
[0006]
Recently, a superlattice APD using a superlattice structure has attracted attention because it is a high-performance light-receiving element that supports high-speed optical communication. Discontinuous energy in the conductor or valence band between the well layer and the barrier layer in the superlattice structure is added to the energy supplied from the electric field to electrons or holes that run perpendicular to the superlattice layer structure under a high electric field. By artificially increasing the collision ionization probability in the vicinity of the band discontinuous interface in the well layer, this multiple effect makes it possible to selectively select high ions of electrons or holes that are different from the collision ionization typical of conventional bulk crystals. Research and development activities that achieve high-speed and low-noise APD have been actively conducted. For example, a mesa-type back-illuminated structure (National Conference of the Institute of Electronics, Information and Communication Engineers 1998, C-3-11) as shown in Fig. 5 is a structure that has been tried to test and realize the high-performance characteristics of superlattice APDs. Well-known, such a structure provides high-performance receiver sensitivity characteristics compared to the hetero-junction functional separation type APD, which is currently mass-produced InGaAs and has a pn junction in the InP layer. Has been shown. However, with such a mesa structure, the pn junction surface with a high electric field necessary for APD operation (an electric field of at least several hundred kV / cm is necessary to induce collision ionization) is exposed on the mesa side wall, and long-term reliability It has become clear that there are concerns about long-term stable operation. Planar superlattices have been proposed and prototyped as methods and structures to avoid and improve this.
[0007]
Fig. 6 shows a schematic cross-sectional view of the proposed planar superlattice APD (IEEE, Journal of Photonics Technology Letters, vol.8, pp.827-829, 1996). As an element structure, p is formed on a semi-insulating InP substrate 61. ⁺ -Buffer layer 62, p ⁻ −InGaAs light absorption layer 63, p ⁺ -InP electric field relaxation layer 64, non-doped InAlAs / InAlGaAs superlattice multiplication layer 65, n ⁺ -InAlAs cap layer 66, n ⁺ -It has a layer structure of an InGaAs contact layer 67, a p-type region 68 serving as a depletion layer termination layer, an annular separation groove 69 for removing a high-concentration adjacent region, and Ti (titanium) ion implantation A planar element is realized by forming the guard ring region 610, the p-type electrode 611, the n-type electrode 612, the passivation film 613, and the AR coating film 614 that serves as a non-reflective film for incident light. Has been. Here, since the depleted InGaAs light absorption layer 63 having a thickness of about 1 μm is provided, the guard ring structure for further reducing the electric field concentration at the periphery of the pn junction is an indispensable element structure although the structure is complicated.
[0008]
More specifically, a conventional example will be described. As disclosed in JP-A-4-286168, an avalanche photodiode (APD) for receiving an optical signal modulated at high speed is based on the same idea as a PIN photodiode having an optical waveguide structure. When trying to realize a waveguide type APD, a guard ring structure for preventing edge breakdown becomes a problem. Therefore, as shown in FIG. 2, the same effect as the guard ring and the light confinement effect can be obtained in the direction transverse to the light traveling direction, and the same effect as the guard ring can be obtained in the light traveling direction. InP-based APD and GaSb-based APD have been devised.
[0009]
Further, as disclosed in Japanese Patent Laid-Open No. 8-242016, the multiplication layer of the mesa structure APD, the protective ring, and the adjacent P ⁺ Perform precise control of layer doping and thickness, and at the same time P ⁺ Very strong electric field at the surface of the layer, as well as P ⁺ Edge yielding at the interface between the layer and the multiplication layer can be avoided. For this purpose, a first conductive type cap layer and a second conductive type avalanche multiplication layer are provided, and the multiplication layer is disposed in the vicinity of the cap layer, whereby the first PN junction is formed. Forming a mesa relief by etching the semiconductor layer; and growing a at least one epitaxial layer on the semiconductor layer to form a guard ring. Avalanche photodiode A manufacturing method was devised.
[0010]
Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 7-31442 (Patent No. 2762939), a superlattice avalanche having a low dark current and a high reliability can be obtained by reducing a surface leakage dark current which is a problem in a mesa type PN junction photodiode. Photodiode with light receiving sensitivity in the wavelength range 1.3-1.5μm, high ionization ratio α / β and low noise , Avalanche photodiode with high-speed response and high reliability Is provided .
[0011]
[Problems to be solved by the invention]
In these conventional mesa type PDs or APDs, the pn junction is exposed on the mesa side wall, so that the dark current is largely unstable, or recently the PD having a waveguide structure has been attracting attention. Since it is not incident from the element surface but is introduced from the end face pn junction, the problem of reliability is particularly great when a large current is input. In the case of a planar structure, the process is complicated and the structure is not necessarily optimal from the viewpoint of cost reduction. It's hard to say.
[0012]
The object of the present invention is to remedy the drawbacks of the prior art described above. Even in the case of the mesa type as described above, the pn junction is terminated on the upper surface of the element while avoiding the formation of a pn junction on the mesa side wall, and the pn junction part is stepped into the element light receiving region from the lower end of the element toward the upper end. Thus, an APD having excellent stability can be provided without providing an additional guard ring structure. This technology can be applied to both APD and PD structures, and can provide a high-reliability element structure that satisfies the basic characteristics of a photodetector, which is low dark current, with a relatively simple process and with a high yield. .
[0013]
[Means for Solving the Problems]
The present invention employs a technical configuration as described below in order to achieve the above-described object.
That is, the aspect of the avalanche photodiode of the present invention is
An avalanche photodiode having a structure in which at least a first conductive type semiconductor layer and a second conductive type semiconductor layer are sequentially stacked on a compound semiconductor substrate, and providing a region of the second conductive type semiconductor layer as a light receiving portion. ,
At the periphery of the light receiving portion of the second conductivity type semiconductor layer, there is a first conductivity type region that forms a pn junction termination on the element surface. Leaving the second conductivity type semiconductor layer at the bottom Further, a part of the first conductivity type region is formed on the outer periphery of the first conductivity type semiconductor layer from the surface of the second conductivity type semiconductor layer.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
By having the above technical configuration, the present invention plays a role as one layer or one region in the first conductive type semiconductor layer as a light absorbing layer and one layer or one region in the second conductive type layer as an avalanche multiplication layer. Avalanche photodiodes , Alternatively, the avalanche photodiode in which the first conductivity type is p type and the second conductivity type is n type or high resistance type. Realize .
[0015]
Further, using InP as the compound semiconductor substrate, the first conductivity type light absorption layer is composed of InGaAs, InAlGaAs or InGaAsP that is easily lattice-matched to the InP substrate, and the second conductivity type avalanche layer is composed of InAlAs, InAlGaAs or InGaAsP. Avalanche photodiodes are provided.
[0016]
Further, after removing the periphery of the second conductivity type light-receiving semiconductor region to the first conductivity type light absorption layer by etching, the periphery of the second conductivity type semiconductor layer including the etched side surface is changed to the first conductivity type as much as possible, and An optical waveguide layer serving as a light guide having a larger forbidden band than the present light absorption layer is provided under the first conductivity type light absorption layer forming the light receiving region, and an optical signal is transmitted from the outside of the device by the optical waveguide. An avalanche photodiode having a waveguide structure is provided, in which incoming and introduced light is photoelectrically converted by being coupled to the light absorption layer by evanescent coupling.
[0017]
If the technical configuration of the present invention is described in more detail, the basic idea of the technical idea of the present invention is to remove the central portion of the light receiving region by means of a pn junction by means of a ground junction and impurity implantation or impurity diffusion after epi growth. In the mesa structure, the pn junction end is not formed on the mesa side wall, and the pn junction termination is formed on the element surface, and the element surface including the pn junction termination is intentionally included. By forming a region that is depleted when a reverse bias is applied, that is, a region that is not subjected to impurity implantation or diffusion, at the lower part of the peripheral portion, the electric field strength in the pn junction termination region under the reverse bias is reduced at the pn junction below the light receiving region. It can be effectively reduced compared with the electric field strength of the element, and it produces an effective guard ring effect without adding a special guard ring structure. An object of the present invention is to provide an element exhibiting low dark current and excellent characteristics even in the avalanche state used.
[0018]
As another aspect of the invention, since a specific element function sharing is provided, a structure in which both a light absorption region and a multiplication region are provided in the second conductivity type is possible. Using this configuration, that is, forming a light absorption layer in the first conductivity type region and an avalanche multiplication region in the second conductivity type region, more effectively provides high speed and low noise characteristics as an APD. realizable.
[0019]
Furthermore, as another aspect of the present invention, when impurity diffusion is adopted as a method for conductivity type conversion, n-type impurity diffusion is diffused compared to the case where formation of a p-type layer and control of the diffusion depth are relatively easy. It is known that the phenomenon itself and its deep depth are difficult to control, and that the conduction type, which has a large ionization rate characteristic of minority carriers as an avalanche layer, is superior in noise characteristics. It defines a conductor type that assumes an n-type avalanche layer having a material property with a collision / ionization rate larger than that of holes. When the hole ionization rate is larger, a configuration using a p-type avalanche layer is desirable.
[0020]
On the other hand, as yet another aspect of the present invention, a combination that matches the above-described aspect when using an InP substrate that is optimal and widely used as a light source / photodetector fabrication substrate in the wavelength band for optical communication is defined. As an optical absorption layer, it can receive all wavelengths of light source made of InGaAsP or InAlGaAs lattice-matched to an InP substrate. InGaAs layer containing 53% In (longest wavelength composition material lattice-matched to InP) Or an InAlGaAs or InGaAsP material having a forbidden band narrower than the forbidden band width of the light-receiving purpose, and an avalanche layer having an ionization rate of electrons larger than that of holes, such as InAlAs, InAlGaAs, InGaAsP, or a combination thereof ( High-speed and low-noise elements can be realized by the (superlattice) structure.
[0021]
Here, for example, in the case of InGaAs, the lattice matching condition is represented as InGaAs having a composition containing 53% In. However, the meaning is that the strain does not cause dislocation. The composition ratio that allows mismatching, or the case where the effective strain due to the multiple layers of the positive strain layer and the negative strain is relaxed in the superlattice structure is included.
[0022]
Further, as another aspect of the present invention, a configuration example in which light is introduced and coupled with a waveguide structure as a waveguide structure is defined, and light is absorbed by the light absorption layer under the avalanche layer region. It defines a structure in which optical carriers are effectively injected into the avalanche region, and is particularly effective in improving and improving internal quantum efficiency in the case of a thin film multiplication layer.
[0023]
【Example】
Hereinafter, specific examples of a semiconductor light receiving element according to the present invention will be described in detail in the form of embodiments with reference to the drawings.
[0024]
(Example 1)
FIG. 1 is a schematic cross-sectional view of a semiconductor light receiving element, APD, according to an embodiment of the present invention. First, p with (100) face ⁺ -On the InP substrate 11, for example, by the gas source MBE method, p ⁺ An impurity concentration of about 5 × 10 by adding Be (beryllium) after forming an InP buffer layer 12 of about 1 μm. ¹⁵ cm ^-3 P ⁻ -InGaAs light absorption layer 13 is formed to 1 μm, and then p ⁺ The InP electric field relaxation layer 14 is grown to 50 nm, the non-doped InAlAs layer 15 without addition of impurities is grown to 2 μm, and finally n by addition of Si or the like ⁺ The InP cap layer 16 is grown by 0.5 μm to form a device wafer. Here, the substrate 11, the layers 12, 13, and 14 correspond to the first conductivity type semiconductor layer of the claims, and the layer 15 corresponds to the second conductivity type semiconductor layer.
[0025]
Using this wafer, first, using a normal photolithography technique (photoresist coating, drying, pattern transfer printing, development / removal of unnecessary parts), for example, a circle having a diameter of 50 μm is left selectively. ⁺ -Remove the InP16 layer. For example, SiO on the surface of the wafer that has undergone this process. ₂ A thin film for use as an impurity diffusion mask is formed, and a photolithographic technique is used to form, for example, a circular n ^- Concentrically with the InP layer 16 leaving a diameter of 100 μm ₂ Remove the thin film. Using this thin film as a diffusion mask, Zn (zinc) is diffused to reach the InGaAs light absorption layer 13 and p ⁺ Region 111 is formed.
[0026]
The actual Zn diffusion is, for example, ZnAs ₂ The wafer patterned with the compound is vacuum-sealed in glass and left at a temperature of 500 to 600 degrees for several hours. The diffusion depth can be controlled by excessive heat treatment time.
[0027]
After this step is finished, again after removing the diffusion mask leaving a diameter of 80 μm, Zn is diffused by a depth of 0.5 μm and p. ⁺ Region 112 is formed.
[0028]
Thereafter, as a protective film on the element surface, for example, SiN is formed by plasma CVD. _x An insulating film 113 is formed to have a thickness of 0.22 μm, and then an n-side electrode 114 and a p-side electrode 115 are formed to complete the device.
[0029]
In this case, the n-side electrode 114 is formed in a ring shape, and light is introduced into the electrode 114. The thickness of the insulating film 113 is set near the AR condition so as to suppress reflection on the incident surface as much as possible with respect to light having a wavelength of 1.3 to 1.55 μm. Light can also be incident on the back side of the substrate. In that case, a circular window may be opened in the p-electrode 115.
[0030]
The avalanche photodiode as the first embodiment of the present invention can be manufactured by the above process. In this device, the breakdown voltage exceeded 100 V, but the multiplication dark current was stable at about 10 nA or less, and a gain / band product of 30 GHz was obtained. Low dark current contributes greatly to crystal quality and guard ring effect. However, by controlling the concentration of the electric field relaxation layer 14, a high electric field of 200 kV / cm or higher is not applied to the InGaAs light absorption layer 13 even when the device breakdown occurs. The effect of suppressing the generation of tunnel current in InGaAs has also appeared. The multiplication factor distribution in the light receiving surface was uniform, and it was stable even after 1000 hours in the breakdown voltage state standing test in a high temperature atmosphere of 150 degrees. This embodiment is an embodiment corresponding to claims 1, 2, 3, 4, and 5.
[0031]
(Example 2)
Next, another embodiment of the present invention will be described with reference to FIG. First, p with (100) face ⁺ -P of about 1μ on InP substrate 21 ⁺ -Thickness 0.5μm, concentration 2 x 10 through InP buffer layer 22 ¹⁹ cm ^-3 P + -InGaAs light absorption layer 23 and a thickness of 0.5 μm, concentration 5 × 10 ¹⁷ cm ^-3 P ^- An InGaAs light absorption layer 24 is formed after growth. This is followed by a 50 nm thick p ⁺ -InP electric field relaxation layer 25, thickness 2 μm, non-doped high resistance InAlAs multiplication layer 26, thickness 0.5 μm, concentration 5 × 10 ¹⁸ cm ^-3 N ⁺ An InP cap contact layer 27 is grown. Here, 21, 22, 23, 24, and 25 correspond to the first conductivity type semiconductor layer of each claim, and 26 corresponds to the second conductivity type semiconductor layer.
[0032]
N of this wafer ^{+ _} For example, SiO on the InP layer 27 ₂ A film is formed on the entire surface of about 0.2 μm, and then the SiO film is selectively left using, for example, a circle having a diameter of 80 μm using a photolithography technique (photoresist coating, drying, pattern transfer printing, development / removal of unnecessary portions). ₂ Then, all of the n + -InP layer 27 is removed.
[0033]
Next, by repeating the same photoresist process as described above, about 1 μm of the i-InAlAs multiplication layer 26 is selectively removed from the upper part by etching while leaving a circle having a diameter of 90 μm on the 80 μm concentric circle.
[0034]
Subsequently, all of the remaining i-InAlAs multiplication layer 26 is removed by a similar photoresist process, leaving a circle having a diameter of 100 μm concentric with the 80, 90 μm circle. By this step, a step is formed on the periphery of the i-InAlAs layer 26 as schematically shown in FIG.
[0035]
Such a wafer is subjected to a Zn diffusion step. Here, the above SiO ₂ Plays the role of a Zn diffusion mask and is the same as described in the first embodiment. ₂ P by heat treatment in the same glass tube ⁺ A diffusion region 211 is obtained. The heat treatment time is adjusted so that the diffusion depth of Zn is about 0.5 μm. After this step, leave a diameter of 30 μm on the circle and concentric circles. ⁺ After removing the InP layer 27, the SiO ₂ Then, for example, a SiNx film 212 of about 0.3 μm is formed as an insulating protective film on the element surface. Next, after polishing the substrate to a predetermined thickness and mirror finishing, a SiNx film of 0.22 μm is also formed on the substrate side. After this, n ⁺ The SiNx film 212 on the InP layer 27 is removed to form an n-type electrode 214, and the n ⁺ -P located under the InP layer 27 ⁺ After the SiNx film outside the SiNx film 213 region on the InP substrate 21 is removed, a p-type electrode 215 is formed in this region to complete the device. Here, light is introduced through the substrate side SiNx film 213.
[0036]
The avalanche photodiode as the second embodiment of the present invention can be manufactured by the above process. In this device, the multiplication dark current was stable at about 5 nA or less, and a gain bandwidth product of 25 GHz was obtained. In this embodiment, the electric field relaxation layer 14 is designed not to apply a high electric field (for example, 300 kV / cm) to the InGaAs light absorption layer 13, but in addition to this, the p-InGaAs layers 23 and 24 are heavily doped. Therefore, since the depletion layer is designed not to spread, generation of dark current due to depletion is suppressed and low dark current is achieved.
[0037]
Although one embodiment of the present invention due to the shape effect due to the etching step has been shown, the multiplication factor distribution in the light receiving surface is also extremely uniform, and even after leaving the breakdown voltage state in a 150 degree atmosphere, it is stable after 1000 hours. there were. The present embodiment is an example in which claims 1, 2, 3, 4, and 5 are embodied.
[0038]
(Example 3)
Another embodiment of the present invention will be described with reference to FIG. First, using a GS-MBE apparatus, a p-type buffer layer 32 of about 1 μm is formed on a semi-insulating InP substrate 31 having a (100) surface, and a p-type film having a thickness of 1 μm ⁺ An InGaAs layer 33 is formed. At this time, by increasing the temperature of the MBE beryllium cell as the concentration of the InGaAs layer 33, about 1 x 10 at the start of growth. ¹⁹ cm ^-3 1 x10 when finished ¹⁷ cm ^-3 In addition, the density change amount is controlled so as to decrease by a linear approximation with respect to the distance by a logarithmic display value of density.
[0039]
This is followed by a 50 nm thick p ⁺ After growing the InP field relaxation layer 34, a non-doped superlattice multiplication layer 35 having a total thickness of 0.3 μm composed of 15 periods of an InAGaAs well layer having a wavelength composition equivalent to 1.2 μm and a thickness of 10 nm and an InAlAs barrier layer having a thickness of 15 nm. And finally n of layer thickness 0.5μm ⁺ An InP cap contact layer 36 is formed. Here, 32, 33 and 34 correspond to the first conductivity type semiconductor layer in the claims, and 35 corresponds to the second conductivity type semiconductor layer.
[0040]
On the n-InP layer 36 of this wafer, for example, SiO ₂ A film is formed on the entire surface of about 0.2 μm, and then the SiO film is selectively left using a photolithography technique (photoresist coating, drying, pattern transfer printing, development / unnecessary portion removal), for example, leaving a circle having a diameter of 60 μm. ₂ And n ⁺ The InP layer 36 is removed. Next, this wafer is ZnAS ₂ In addition, the superlattice layer 35 is completely p-typed by enclosing it in a glass tube and applying sufficient heat treatment. ⁺ A diffusion region 311 is formed.
[0041]
Next, by repeating the same photoresist process as described above, the SiO 50 diameter is left concentrically with the 60 μm circle, leaving a 50 μm diameter circle. ₂ And the n-InP layer 26 are removed, and the same heat treatment as described above is performed to make one region of the upper portion of the superlattice layer 35 p. ⁺ A diffusion region 312 is assumed. After this step, the remaining n-InP layer 36 is removed by a photoresist step, leaving a circle with a diameter of 30 μm concentric with the 60, 50 μm circle.
[0042]
After this, the SiO ₂ Then, for example, a SiNx film 313 is formed to have a thickness of 0.3 μm as a surface insulating protective film. After that, an SiNx film 314 of about 0.22 μm is formed on the substrate surface with the substrate thickness adjusted and mirrored to reduce reflection with respect to the optical communication wavelength, and an n electrode 315 and a p electrode 316 are formed to form an element. Complete. Here, light is incident from the back and substrate sides, and the p-electrode is on the front side. From It has a structure to take out. With this configuration, the device can be flip-chip assembled on a sub-mount in which lead electrodes are formed in advance, and wire bonding to the device is not necessary.
[0043]
The avalanche photodiode which is the third embodiment of the present invention can be manufactured by the above process. In this device, the multiplication dark current is stable at about 1 nA or less, and a high speed characteristic of a gain bandwidth product of 120 GHz is obtained. In this embodiment, the electric field relaxation layer 34 is designed not to apply a high electric field (200 kV / cm) to the InGaAs light absorption layer 33. In addition to this, the concentration doping of the p-InGaAs layer 33 starts from the pn junction. By adopting a configuration in which the concentration increases as the distance increases, electrons, which are optical carriers generated by optical signals in InGaAs, are drifted to the pn junction at a high speed by the internal electric field due to the concentration gradient. And high speed has been achieved. This embodiment is also an example in which claims 1, 2, 3, 4, and 5 are embodied.
[0044]
(Example 4)
Next, another embodiment of the present invention, an avalanche photodiode having a waveguide structure, will be described with reference to the device schematic diagram of FIG. FIG. A is a schematic cross-sectional view, and FIG. First, using a GS-MBE apparatus, a non-doped InP layer 42 having a thickness of about 1 μm is first grown on a semi-insulating InP substrate 41 having a (100) plane, and then a thickness of 600 nm is equivalent to a composition wavelength of 1.05 μm. A non-doped InAlGaAs optical waveguide layer 43, a non-doped InAlGaAs layer 44 having a thickness of 40 nm and a composition wavelength of 1.15 μm, and a non-doped InP etching / stop layer 45 having a thickness of 20 nm are sequentially formed.
[0045]
Following this, a thickness of 40 nm and a concentration of 5x10 ¹⁸ cm ^-3 The composition wavelength of 1.15μm p ⁺ An InAlGaAs layer 46 and a p-InGaAs light absorption layer 47 having a thickness of 500 nm are formed.
[0046]
At this time, by changing the temperature of the MBE beryllium cell as the concentration of the p-InGaAs layer 47, about 1 x 10 at the start of growth. ¹⁹ cm ^-3 1x10 at the end ¹⁷ cm ^-3 In addition, control is performed so that the density change amount is a logarithmic display value of density and is reduced by linear approximation with respect to distance.
[0047]
This is followed by a 50 nm thick p ⁺ -InP electric field relaxation layer 48, a 200 nm thick non-doped InAlAs multiplication layer 49 is formed, and finally an n thickness of 500 nm is formed. ⁺ An InP cap contact layer 50 is formed. Here, 46, 47 and 48 correspond to the first conductivity type semiconductor layer in the claims, and 49 corresponds to the second conductivity type semiconductor layer.
[0048]
Using such a wafer, the device fabrication process is started. First, the n + -InP layer 50 is selectively removed using photolithography technology, leaving 6 μm × 20 μm.
[0049]
Next, the InAlAs multiplication layer 49, p, with the same work and the same 14 μm x 28 μm shape but the same center as the 6 μm x 20 μm shape. ⁺ The -InP electric field relaxation layer 48 and the p-InGaAs light absorption layer 47 are selectively removed. Thereafter, a photoresist is formed only on the similar region of 10 μm × 24 μm by photolithography.
[0050]
Using such an ion implantation technique, beryllium ions are implanted into such a wafer. The implantation is, for example, an acceleration voltage of 20 kV / cm and a dose of 5 x 10 ¹² cm ^-2 Perform under conditions. At this time, in the region covered with the photoresist, the implanted beryllium stops in the photoresist. After the ion implantation process, the photoresist is removed, and an instantaneous heat treatment process of about 600 degrees 20 seconds is performed. By going p ⁺ Region 411 is formed. Next, for example, a SiNx film 412 is formed as an insulating surface protection film on the entire surface of the wafer, and the p + -InAlGaAs layer 46 is selectively removed leaving a 20 μm × 36 μm region similar to the mesa region.
[0051]
Next, as shown in FIG. B, a waveguide having a width of 7 μm is formed so that the center of the waveguide coincides with the center line in the longitudinal direction of the light receiving element. At this time, the InAlGaAs layers 44 and 43 are selectively removed by using the n-InP layer 45 as a mask. At this time, in the light receiving area, the above 20 μm x 36 μm p ⁺ -The outer periphery of the InAlGaAs layer 46 remains. Thereafter, after the n-side electrode 413 and the p-side electrode 414 are formed, a light incident end face is formed by cleaving the wafer in a direction perpendicular to the optical waveguide, and the surface is made non-reflective with respect to the incident light. An avalanche photodiode with a waveguide is completed by forming a SiNx film 415 having a thickness that satisfies the conditions, for example, about 220 nm.
[0052]
The avalanche photodiode which is the fourth embodiment of the present invention can be manufactured by the above process. In this device, the multiplication dark current is stable at about 1 nA or less, and a high-speed characteristic with a gain bandwidth product of 100 GHz is obtained at an operating voltage of about 18V. This embodiment is also an example in which claim 6 is embodied. In this structure, the optical signal is introduced into the light absorption layer from the optical waveguide by evanescent coupling, and light is not introduced into the end face of the pn junction, so it is stable against a large amount of light, that is, a large current signal light. Operate. In addition, the high-sensitivity APD in the waveguide configuration has a feature that the semiconductor laser as a light source has good compatibility with the waveguide configuration, that is, the light is handled in the lateral direction, and has excellent features such as integration.
[0053]
【The invention's effect】
In the present invention, by combining conventional relatively simple technologies without introducing new new technologies, a semiconductor light-receiving device having excellent reliability with low dark current, which is a basic performance, can be obtained with high reproducibility. It can be produced. Specifically, when the multiplication layer thickness is thin, it is more certain to use a technique such as ion implantation, but the effective guard ring effect can be made relatively simple and effective using conventional diffusion techniques. Realized the characteristics that can be formed and has excellent reliability. Although an example of an avalanche photodiode that requires a high electric field is shown in the present invention, it goes without saying that the structure and the manufacturing method are effective even in a photodiode that does not require a high electric field.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a configuration of an avalanche photodiode using a compound semiconductor according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing a configuration of an avalanche photodiode according to another embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a configuration of an avalanche photodiode according to another embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of an avalanche photodiode having a waveguide structure according to another embodiment of the present invention. FIG. A is a schematic cross-sectional view of the element, and FIG. B is a schematic top view of the element.
FIG. 5 is a diagram showing a structure of a mesa superlattice APD according to a conventional example.
FIG. 6 is a diagram showing a structure of another planar superlattice APD according to a conventional example.
[Explanation of symbols]
11 p ⁺ -InP substrate
12 p ⁺ -InP buffer layer
13 p ⁻ -InGaAs light absorption layer
14 p ⁺ -InP electric field relaxation layer
15 Non-doped InAlAs multiplication layer
16 n ⁺ −InP cap layer
111 p ⁺ Region I
112 p ⁺ Region II
113 Antireflection insulating film
114 n electrode
115 p-electrode
21 p ⁺ -InP substrate
22 p ⁺ -InP buffer layer
23 p ⁺ -InGaAs light absorption layer
24 p ^−_ InGaAs light absorption layer
25 p ⁺ -InP electric field relaxation layer
26 Non-doped i-InAlAs multiplication layer
27 n ⁺ -InP cap layer
211 p ⁺ Diffusion area
212 Insulating film
213 Antireflection insulating film
214 n-side electrode
215 p-side electrode
31 Semi-insulating InP substrate
32 p ⁺ -Buffer layer
33 p-InGaAs light absorption layer
34 p ⁺ -InP electric field relaxation layer
35 Non-doped superlattice multiplication layer
36 n ⁺ -InP cap contact layer
311 p + diffusion region
312 p ⁺ Diffusion area
313 Insulating protective film
314 Non-reflective film
315 n-type electrode
316 p-type electrode
41 Semi-insulating InP substrate
42 Non-doped InP layer
43 Non-doped InAlGaAs optical waveguide layer
44 Non-doped InAlGaAs layer
45 Non-doped InP layer
46 p ⁺ -InAlGaAs layer
47 p-InGaAs light absorption layer
48 p ⁺ -InP electric field relaxation layer
49 Non-doped InAlAs multiplication layer
50 n ⁺ -InP cap contact layer
411 p ⁺ region
412 SiNx insulating protective film
413 n-side electrode
414 p-side electrode
415 SiNx antireflection film
51 n-type InP substrate
52 n-type InP buffer layer
53 Superlattice multiplication layer
54 p-type InP electric field relaxation layer
55 p-type InGaAs light absorption layer
56 p-type InP cap layer
57 p ⁺ Type InGaAs cap layer
58 Light receiving area
59 Passivation membrane
510 p-electrode
511 n electrode
512 AR non-reflective coating film
61 Semi-insulating InP substrate
62 p ⁺ Type buffer layer
63 p-type InGaAs light absorption layer
64 p-type InP electric field relaxation layer
65 Non-doped InAlAs / InAlGaAs superlattice multiplication layer
66 n + type InAlAs cap layer
67 n + type InGaAs contact layer
68 p-type region
69 Annular separation groove
610 Guard ring
611 p-electrode
612 n electrode
613 Passivation film
614 AR coat

Claims (6)

An avalanche photodiode having a structure in which at least a first conductive type semiconductor layer and a second conductive type semiconductor layer are sequentially stacked on a compound semiconductor substrate, and providing a region of the second conductive type semiconductor layer as a light receiving portion. ,
A first conductivity type region for forming a pn junction termination portion on the element surface is formed at a periphery of the light receiving portion of the second conductivity type semiconductor layer, leaving a second conductivity type semiconductor layer at a lower portion. In the avalanche photodiode, a part of the first conductivity type region reaches the first conductivity type semiconductor layer from a surface of the second conductivity type semiconductor layer. One layer or one region in the first conductive type semiconductor layer is a light absorption layer, and one layer or one region of the second conductive type layer is formed with a high electric field when reverse bias is applied, thereby performing impact ionization / avalanche multiplication. The avalanche photodiode according to claim 1, wherein the avalanche photodiode is a layer. 3. The avalanche photodiode according to claim 1, wherein the first conductivity type is p-type and the second conductivity type is n-type or high-resistance type. InP is used as the semiconductor substrate, the first conductivity type light absorption layer is composed of InGaAs, InAlGaAs or InGaAsP lattice matched to the InP substrate, and the second conductivity type avalanche layer is composed of InAlAs or InAlGaAs or InGaAsP lattice matched to the InP substrate. The avalanche photodiode according to claim 2, wherein the avalanche photodiode is provided. The etching process removes at least the periphery of the second conductivity type region outside the light receiving region to the first conductivity type light absorption layer, and serves as a waveguide / introduction path for the optical signal under the first conductivity type light absorption layer. 5. The avalanche photodiode having a waveguide structure according to claim 2, further comprising an optical waveguide layer having a forbidden band larger than a forbidden band width of the light absorption layer formed. Selective for a device wafer in which a light absorption layer and an electric field relaxation layer to which a p-type impurity is added, an n-type multiplication layer, and a cap layer to which an n-type impurity is added are sequentially laminated on a semiconductor substrate Removing the n-type cap layer leaving a circular portion in
Forming a concentric impurity diffusion first mask having a diameter larger than that of the circular n-type cap layer on the wafer surface;
Diffusing p-type impurities from the surface until reaching the light absorption layer using the first mask for impurity diffusion to form a p-type region;
Forming a second concentric impurity diffusion mask that is smaller in diameter than the first impurity diffusion mask and larger in diameter than the circular portion;
Diffusing p-type impurities using the second impurity diffusion mask to form a p-type region on the surface of the multiplication layer leaving an n-type multiplication layer below;
A method for manufacturing an avalanche photodiode comprising:

Images