JPH077180A - Light emitting element - Google Patents

Abstract

PURPOSE:To provide a light emitting element made of porous silicon in which high degree of freedom is ensured in the selection of emission spectrum while realizing emission characteristics which can not be achieved conventionally. CONSTITUTION:The light emitting element comprises a porous silicon substrate 21 obtained through anodic oxidation of a single crystal silicon substrate having a plurality of regions in which at least one of the type or the concentration of dopant is different in the planar direction, and electrodes 22, 24 formed, directly or indirectly, on the opposite sides of the porous silicon substrate 21 in order to apply voltage to the porous silicon substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to improvement of a light emitting device constructed by using a porous silicon substrate having a surface made porous by anodic oxidation.

[0002]

2. Description of the Related Art Conventionally, EL (electroluminescence)
Direct transition type compound semiconductors have been mainly used as light emitting elements such as elements, light emitting diodes, and laser diodes, but in recent years, porous silicon obtained by using indirect transition type single crystal silicon as a starting material emits light. It has been studied as a material for devices (Appl. Phys. L
ett. Vol. 57, pp. 1046-1048 (19
90) etc.).

Since crystalline silicon has a narrow band gap of indirect transition type, it does not normally emit visible light. However, it is clear that the porous silicon layer formed on the surface by anodizing single crystal silicon in an aqueous solution of hydrogen fluoride (HF) at a current density lower than that of the electrolytic polishing region emits visible light at room temperature. Has been In this case, the starting material is homogeneous p-type or n-type.
A single crystal silicon substrate of the type is used.

[0004]

In a conventional light emitting device using porous silicon, a homogeneous p-type or n-type single crystal silicon substrate as described above is used as a starting material. Therefore, the emission spectrum of the obtained porous silicon is substantially uniform in the plane, and when a light emitting device having a large area is to be constructed, there is a problem that the degree of freedom in selecting the obtained emission spectrum is small. .

An object of the present invention is to provide a light emitting device using porous silicon, which can increase the degree of freedom in selection of an emission spectrum and can realize light emitting characteristics which could not be obtained in the past. is there.

[0006]

The present invention is a light emitting device using the above-described porous silicon, and is characterized by having the following constitution, thereby achieving the above object.

That is, the present invention provides a porous silicon substrate having a surface made porous by anodic oxidation of a crystalline silicon substrate having a plurality of regions in which at least one of the type and concentration of the dopant is different in the in-plane direction. An electrode that is formed directly or indirectly on both surfaces of the porous silicon substrate and that applies a voltage to the porous silicon.

[0008]

The emission spectrum of porous silicon has a Gaussian shape, but its peak position and full width at half maximum depend on the state of porous silicon formed by anodic oxidation.
The present invention, as described above, the luminescent characteristics of porous silicon,
In view of dependence on the state of porous silicon, by anodizing a crystalline silicon substrate having a plurality of regions having different dopant concentrations and types of dopant in the in-plane direction within the same substrate, It is characterized in that a porous silicon substrate having a plurality of different regions in the in-plane direction is formed, and thereby a plurality of regions having different emission characteristics in the in-plane direction is formed.

That is, since the light emitting device of the present invention is constituted by using as a starting material a crystalline silicon substrate having a plurality of regions in which at least one of the kind and the concentration of the dopant is different in the in-plane direction, Porous silicon formed by oxidation exhibits different emission characteristics in the in-plane direction.

Therefore, by devising the type and concentration of the dopant in the plurality of regions of the crystalline silicon substrate, the emission characteristics in the plurality of regions of the porous silicon substrate are made different, so that these are different as a whole. The light emission characteristic obtained as the sum of the light emission characteristics is realized. Therefore, it is possible to realize the light emitting characteristics which cannot be obtained by the conventional porous silicon light emitting device using the homogeneous crystalline silicon substrate as the starting material.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing embodiments with reference to the drawings.

FIGS. 1 (a) to 1 (d) are schematic plan views for explaining four types of single crystal silicon substrates prepared as starting materials for porous silicon. 1 (a)-
The single crystal silicon substrate shown in (d) is configured using a (111) single crystal silicon substrate. Further, although each of the single crystal silicon substrates 1 to 4 is doped with impurities from one surface side thereof, it is not uniformly doped, and each of the 16 divided regions is shown in the drawing. Doping is carried out under the conditions shown by symbols a to d. Details of the dopings a to d are shown in Table 1 below.

[0013]

[Table 1]

As is clear from Table 1 and FIG. 1, for example, when the single crystal silicon substrate 1 is taken as an example, a region doped under the condition a and a region doped under the condition b are illustrated. Are mixed in. That is, a plurality of regions having different concentrations of B, which is a p-type dopant, are formed in the in-plane direction. Similarly, with respect to the other single crystal silicon substrates 2 to 4, a plurality of regions having different dopant concentrations and types of dopants are mixed in the in-plane direction.

The above-mentioned dopings a to d can be carried out according to known doping techniques, and typically, the following four kinds of methods can be mentioned. Focused ion beam (FIB) method ... This method uses, for example, 5 × 10 ¹³ to 1 at an acceleration energy of 200 KeV.
This can be performed by doping B or P at a concentration of × 10 ¹⁵ / cm ² and then annealing at 600 ° C. for 1 hour.

Laser doping method: In this method, for example, B ₂ H ₆ or PH ₃ gas is filled in a vacuum chamber, the substrate temperature is kept constant at about 200 ° C., and an excimer laser (wavelength 325 n
m) is irradiated to perform doping, and the temperature is 900 ° C.
This can be achieved by performing thermal diffusion at a temperature of ~ 1000 ° C. The concentration of B or P is 1 to 3 in terms of resistivity.
By controlling in the region of 0 Ωcm, the resistivity shown in Table 1 can be realized.

Ion implantation method: A non-implanted region is covered with a resist, and an ion implantation apparatus is used to, for example, 200 KeV.
5 × 10 ¹³ to 1 × 10 ¹⁵ / c depending on the acceleration energy of
After doping B or P at a concentration of about m ² , 60
This can be done by thermal annealing at a temperature of 0 ° C. for 1 hour.

Screen printing + thermal diffusion method: By a screen printing method, the injection region is covered with a resist containing B or P in liquid SiO ₂ and thermal diffusion is performed at a temperature of about 900 ° C to 1000 ° C. By controlling the concentration of B or P in the region where the resistivity is 1 to 30 Ωcm,
The resistivity shown in Table 1 can be realized.

In this example, among the doping methods shown in the above 1 to 4, the single crystal silicon substrates 1 to 4 shown in FIG. 1 were prepared by the FIB method. On the other hand, four types of single crystal silicon substrates uniformly doped with the above dopings a to d were prepared and made porous. The process of making porous will be described with reference to FIG.

In FIG. 2, a single crystal silicon substrate 6 doped under the condition a in Table 1 is immersed in a 45 wt% HF aqueous solution 5. On the back surface of the single crystal silicon substrate 6, a p ⁺ -type single crystal silicon substrate 7 and an electrode 8 made of aluminum are laminated in this order. Reference numeral 9 indicates a support member made of synthetic resin or wax.

In order to make porous, an electric current is passed between the electrode 10 and the electrode 8 made of platinum, which are also immersed in the HF aqueous solution 5, and the single crystal silicon substrate 6 is applied at a current density of 25 mA / cm ^2. Anodized. In addition, porous S
In order to promote i conversion, light was irradiated by a 500 W tungsten lamp.

As described above, the surface of the doped single crystal silicon substrate 6 was made into porous silicon to obtain a porous silicon substrate. Using the obtained porous silicon substrate, the light emitting device shown in FIG. 4 was constructed.

In FIG. 4, reference numeral 11 denotes the porous silicon substrate obtained as described above, and the exposed surface side thereof is made porous silicon by the anodization. On the back side of the porous silicon substrate 11, p ⁺ obtained by doping a single crystal silicon substrate with impurities.
A single crystal silicon substrate 7 for forming layers and an electrode 8 made of aluminum are laminated in this order. Further, 12 is a transparent electrode containing Au as a main component.

Using each of the single crystal silicon substrates uniformly doped according to the doping conditions b to d in Table 1, the surface was anodized in the same manner as described above to form porous silicon, and the obtained porous silicon substrate was obtained. Were used to form light emitting devices having the structures shown in FIG.

Four types of porous silicon light-emitting devices were manufactured using the single crystal silicon substrates doped under the doping conditions a to d as described above as starting materials, and the emission spectra of each were measured. The results are shown in Fig. 3.

FIGS. 3 (a) to 3 (d) show emission spectra of a light emitting device constituted by using as a starting material a single crystal silicon substrate which is porous siliconized under the above doping conditions a to d, respectively. As is clear from comparison between FIGS. 3A and 3B, the peak position of the emission spectrum is shifted to the short wavelength side by increasing the resistivity by changing the concentration of B which is a p-type dopant. I understand. Similarly, from the comparison between FIGS. 3C and 3D, the peak position of the emission spectrum shifts to the short wavelength side even when the resistivity is increased by changing the concentration of P, which is an n-type dopant. I understand. Therefore, it is understood that the peak position of the emission spectrum can be shifted to the short wavelength side by using the high-resistance single crystal silicon substrate regardless of the p-type and n-type conductivity types.

Further, as is clear from the comparison between the emission spectra of FIGS. 3 (a) and 3 (b) and the emission spectra of FIGS. 3 (c) and 3 (d), the n-type porous silicon is more p-type. It can be seen that the peak position of the emission spectrum is on the shorter wavelength side than that of the porous silicon.

Therefore, as is clear from the results shown in FIGS. 3A to 3D, by using the single crystal silicon substrate configured so that the kind and the concentration of the dopant are different,
It can be seen that the peak position of the emission spectrum can be controlled.

The light emitting device of this embodiment is based on the above knowledge, and is shown in FIG.
As shown in (d), one surface of each of the single crystal silicon substrates 1 to 4 is divided into 16 regions, and each region is subjected to the doping condition a.
To d are used to form a plurality of regions having different types and concentrations of dopants in the in-plane direction.

FIG. 5 is a sectional view of a light emitting device according to an embodiment of the present invention. 21 indicates a porous silicon substrate,
As shown in FIG. 1A, the single crystal silicon substrate 1 in which each region is doped under the doping condition a or b is used as a starting material, and anodization is performed in the same manner as described above.
The surface is made of porous silicon. On the back surface of the porous silicon substrate 21, a single crystal silicon substrate 23 as a p ⁺ layer and an electrode 24 made of aluminum are laminated in this order, and on the surface side of the porous silicon substrate 21, a transparent made of Au is formed. The electrode 22 is formed.

Light-emitting element 25 constructed as described above
The emission spectrum of is shown in FIG. As is clear from FIG. 6A, by using the porous silicon substrate obtained by making the single crystal silicon substrate 1 shown in FIG. It can be seen that an emission spectrum corresponding to the sum of the emission spectra shown in b) is realized. That is, when a porous silicon substrate is obtained by using the single crystal silicon substrate 1 in which a plurality of regions indicated by the doping conditions a and b are mixed as a starting material, a light emission formed by using the porous silicon substrate. It can be seen that the emission spectrum of the device is the sum of the emission spectrum of the porous silicon under the doping condition a and the emission spectrum of the porous silicon under the doping condition b.

Similarly, as shown in FIGS. 1 (b) to 1 (d), single crystal silicon substrates 2 to 4 in which the respective regions are doped are used as starting materials, respectively.
A light emitting device having the structure shown in was constructed and the emission spectrum was measured. The results are shown in FIGS. 6 (b) to 6 (d).

As is apparent from FIGS. 6 (b) to 6 (d),
The emission spectra of these light-emitting elements are respectively combined according to the doping conditions of each region in the single crystal silicon substrates 2 to 4 used as starting materials, that is, the state of porous silicon obtained by anodization. hand,
The emission spectra shown in FIGS. 6B to 6D are shown.

As described above, in the light emitting device of the present embodiment, the single crystal silicon substrate used as the starting material is provided with a plurality of regions having different kinds and concentrations of the dopant in the in-plane direction. Therefore, when the surface is made porous silicon by the above-mentioned anodization, the state of the obtained porous silicon layer is changed by the above doping conditions, so that the obtained porous silicon substrate has a plurality of regions having different emission characteristics. Is configured.

Therefore, as shown in FIGS. 6 (a) to 6 (d), various doping conditions can be selected by selecting the doping conditions of the plurality of regions and by devising a method of combining the plurality of regions. It is possible to realize light emission characteristics.

According to the experiments conducted by the inventors of the present application, even when the doping methods shown in 1 to 3 are used instead of the FIB method, the n-type dopant is used as in the case of the above embodiment. By using, it is possible to shift the peak position of the emission spectrum to the short wavelength side as compared with the case of using a p-type dopant, and by increasing the resistivity, the peak position of the emission spectrum is shifted to the short wavelength side. It was confirmed that a light emitting element having various light emitting characteristics can be constructed similarly to the above-mentioned embodiment.

FIG. 7 is an exploded perspective view showing an application example of the present invention and showing an example in which a matrix display device is constructed by combining with a thin film transistor (hereinafter abbreviated as TFT). In FIG. 7, the translucent glass substrate 3
A plurality of transparent electrodes 32 made of, for example, ITO for driving the light emitting element are formed on the substrate 1 in a matrix. Further, each transparent electrode 32 has one TFT.
33 is connected.

On the other hand, the upper electrode 3 made of aluminum
4, a plurality of light emitting elements 35 according to the embodiment of the present invention are provided.
Are fixed in a matrix. In the display device shown in FIG. 7, one TFT made of polycrystalline silicon is arranged below each light emitting element 35 made of porous silicon, and a bead feeder fills a space between them. It is manufactured by coating the side surface with liquid SiO ₂ and fixing it. The wiring is the light emitting part and the TFT3.
It is sufficient to pull out from 3 respectively.

Thus, the light emitting device according to the present invention is
It can be preferably used for forming each unit light emitting element when forming a matrix type display device using a TFT.

[0040]

According to the present invention, a crystalline silicon substrate having a plurality of regions having different types and / or concentrations of dopants in the in-plane direction is used as a starting material, and the crystalline silicon substrate is anodized. Since the light-emitting element is configured by using a porous silicon substrate whose surface is made porous, in a plurality of regions in which at least one of the type and concentration of the dopant of the porous silicon substrate is different. The surface state of the porous silicon is made different.

Therefore, a plurality of porous silicon regions having different surface states exhibit different emission characteristics, and as a whole, an emission spectrum which is the sum of the above different emission characteristics is realized. By devising the kind and concentration of the dopant and the arrangement of a plurality of regions in the above, it is possible to provide a light emitting device having a light emission characteristic which has not been obtained hitherto, and it is possible to expand the degree of freedom in selecting an emission spectrum. .

[Brief description of drawings]

1A to 1D are schematic plan views for explaining doping conditions of respective regions of a surface of a single crystal silicon substrate used as a starting material in Examples of the present invention.

FIG. 2 is a sectional view for explaining a process of anodizing.

3 (a) to (d) are diagrams showing emission spectra of porous silicon formed by using a single crystal silicon substrate doped under the doping conditions a to d shown in Table 1, respectively.

FIG. 4 is a cross-sectional view showing a light emitting device configured to measure the emission spectrum shown in FIG.

FIG. 5 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention.

6A to 6D are respectively FIG. 1A to FIG.
The figure which shows the emission spectrum of the light emitting element of the Example which used the porous silicon substrate produced from the single crystal silicon substrate which each region doped as shown in (d) as a starting material.

FIG. 7 is an exploded perspective view for explaining a display device as an application example of the present invention.

[Explanation of symbols]

 1 to 4 ... Single crystal silicon substrate 11 ... Porous silicon substrate 7 ... Electrode 12 ... Electrode 21 ... Porous silicon substrate 22 ... Electrode 24 ... Electrode 25 ... Light emitting element 35 ... Light emitting element 34 ... Electrode

Claims (1)

[Claims] 1. A porous silicon substrate having a surface made porous by anodic oxidation of a crystalline silicon substrate in which at least one of a kind and a concentration of a dopant is different in an in-plane direction, and both surfaces of the porous silicon substrate. A light emitting element, which is directly or indirectly formed on the porous silicon substrate and has an electrode for applying a voltage to the porous silicon substrate.