JP2002280603A - Optical functional element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element having large light emitting intensity or a photodetecting element having good photodetecting sensitivity, in order to solve the problems of a low light emitting intensity of the emitting element and low photodetecting sensitivity of the photodetecting element. SOLUTION: An optical functional element comprises an amorphous silicon film 5 containing crystal silicon particles 4 and is formed by embedding the film 5 in holes 2 of a porous region 3 formed on a single crystal silicon substrate 1 and heating the film 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical functional device such as a light emitting device or a light receiving device.

[0002]

2. Description of the Related Art At present, light emitting diodes and laser diodes as light emitting elements are used in optical communication devices, display devices and optical integrated circuits, and photodiodes as light receiving elements are used in solar cells and the like. ing. Conventionally, these optical functional elements are made of GaAs (gallium arsenide) or GaN.
(Gallium nitride) and the like.

In recent years, it has been reported that porous silicon formed by anodizing single crystal silicon in a hydrofluoric acid solution exhibits strong photoluminescence at room temperature.
0 (Appl. Phys. Lett.
57, 1046 1990). This presentation showed the possibility of realizing an optical functional element such as a light emitting element using silicon, which was considered to be difficult to emit light because it was an indirect transition semiconductor.

[0004] Then, as an actual light emitting element, it was realized by Koshida et al. (Appl. Phys. Lett.
60 (3), 20 January 1992). This conventional light emitting device will be described with reference to FIG. FIG. 6 is a cross-sectional view of a conventional light emitting device.

As shown in FIG. 6, a porous region 103 having a plurality of holes 102 is formed in a single crystal p-type silicon substrate 101 by performing anodization.
Are formed on a silicon substrate 101 to form a carrier injection electrode 105 made of a polypyrrole film which is a conductive polymer material. A translucent display electrode 106 is formed on the carrier injection electrode 105 by gold deposition. On the back surface of the silicon substrate 101, an ohmic electrode 107 of aluminum is formed. The structure of the light receiving element is the same as that shown in FIG.

Here, the structure of the plurality of holes 102 formed by anodization varies depending on the type of the silicon substrate 101, the specific resistance of the silicon substrate 101, the current value at the time of anodization, and the like. Has a cylindrical shape, and its wall surface is uneven.

[0007]

However, the conventional light emitting device has a problem that it cannot be actually used in an optical communication device or the like because of its low light emission intensity. Similarly, the light-receiving element also had poor light-receiving sensitivity, so that it could not be actually used in an optical communication device or the like.

An object of the present invention is to solve the problem that the light emitting intensity of the light emitting element is low and the light receiving sensitivity of the light receiving element is low in the light emitting element or the light receiving element using silicon. It is an object of the present invention to provide a light-emitting element having high emission intensity or a light-receiving element having good light-receiving sensitivity.

[0009]

A clear cause of light emission from a light emitting device using a silicon substrate having a porous region is not clear. However, since it has been found that crystalline silicon particles are formed on the wall surfaces of the holes formed by anodization, it is considered that the crystalline silicon particles formed on the wall surfaces of the holes contribute to light emission. That is, the problem that the light emission intensity of the conventional light emitting element is low or the problem that the light receiving sensitivity of the conventional light receiving element is poor can be considered to be one of the causes of the small number of crystalline silicon particles in the pores in the porous region.

[0010] An optical functional device according to the present invention comprises a silicon substrate, a plurality of holes formed in the silicon substrate, crystalline silicon particles in the holes, and silicon filling the holes. Things.

[0011] Thus, when current is injected by embedding silicon in the hole of the silicon substrate, the efficiency of electron injection into the crystalline silicon particles in the hole can be increased, and conversely, when light is received. Can increase the mobility of electrons and holes generated by optical coupling.

In the method of manufacturing an optical functional device according to the present invention, a first step of forming a hole in a silicon substrate and a second step of forming amorphous or microcrystalline silicon in the hole after the first step. And a third step of heat-treating the silicon substrate after the second step.

According to the method of manufacturing an optical functional device according to the present invention, a portion of the amorphous or microcrystalline silicon formed in the hole of the silicon substrate in the second step is subjected to the heat treatment in the third step. It can be transformed into crystalline silicon particles.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical functional device and a method for manufacturing the same according to an embodiment of the present invention will be described below in detail with reference to FIGS. In the following embodiments, a light emitting element will be mainly described as one of the optical function elements, but the light receiving element has the same structure.

FIG. 1 is a sectional view of a light emitting device according to an embodiment of the present invention.

As shown in FIG. 1, in a light emitting device according to the present invention, a porous region 3 in which many fine holes 2 are formed is formed on a surface of a p-type single crystal silicon substrate 1. Here, the porous region 3 refers to a region where a plurality of holes 2 exist on the surface of the silicon substrate 1.

A plurality of crystalline silicon particles 4 having a particle size of about 1 nm to 10 nm are formed in each hole 2 of the porous region 3. The silicon film 5 is embedded in the hole 2 and formed on the surface of the silicon substrate 1. The crystalline silicon particles 4 are scattered and distributed in the silicon film 5 in the holes 2. The crystalline silicon particles 4 are formed not only in the holes 2 but also in the silicon film 5 on the silicon substrate 1.

A translucent display electrode 6 made of gold is formed on the silicon film 5. Further, on the back surface of the silicon substrate 1, an ohmic electrode 7 made of aluminum is formed. In addition, as a material of the display electrode 6,
A composite oxide of In (indium) and Sn (tin) as a transparent material (hereinafter, referred to as “ITO”) may be used.

The light emitting device according to the embodiment of the present invention has a hole 2
Since a silicon film 5 made of the same element as the silicon substrate 1 is formed therein instead of a polymer material, the efficiency of injecting electrons into the crystalline silicon particles 4 can be increased when a current is applied to the light emitting device. it can. Conversely, when used as a light receiving element, the mobility of electrons and holes generated by optical coupling can be increased.

Next, a method of manufacturing a light emitting device according to an embodiment of the present invention will be described step by step with reference to FIG. FIG. 2 is a process sectional view showing a method for manufacturing a light emitting device according to an embodiment of the present invention.

<Backside Vapor Deposition Step> As shown in FIG. 2A, an ohmic electrode 7 is first formed on the backside of a p-type single crystal silicon substrate 1 by EB (electron beam) deposition of aluminum. The silicon substrate 1
Is used with a plane orientation of (100) and a resistivity of 8 to 12 Ωcm. This step is performed in order to use the ohmic electrode 7 as an anode electrode in the next step.

<Anodizing Step> Next, as shown in FIG. 2B, by anodizing the silicon substrate 1, a porous region 3 having a plurality of holes 2 near the surface of the silicon substrate 1 is formed. Form. At this time, crystalline silicon particles having a particle size of about 1 nm to about 10 nm are formed on the wall surface of the hole 2. In FIG. 2, the holes 2 are shown as regularly and uniformly formed. However, in reality, the shapes of the holes 2 are different from each other, and are basically cylindrical, and the wall surface is uneven.

Here, anodization according to an embodiment of the present invention will be described with reference to FIG. FIG. 3 is a sectional view schematically showing an anodizing apparatus for anodizing.

As shown in FIG. 3, portions other than the portion where the porous region is formed on the silicon substrate 1 (the side surface, the back surface, and a part of the front surface) are covered with a fluororesin 8 such as Teflon (registered trademark). The ohmic side of the constant current source 9 is
And the cathode side of the constant current source 9 is connected to the platinum electrode 10, and the silicon substrate 1 and the platinum electrode 10 are connected to a solution (ethyl alcohol: hydrofluoric acid (48% aqueous solution) = 1) in a Teflon tank 11. : 1) Immerse in 12.

Thereafter, the current density is adjusted to 5 using the constant current source 9.
Anodization is carried out for about 1 to 5 minutes while fixing at ５０50 mA / cm ² . As a result, a large number of holes 2 are formed on the surface of the silicon substrate 1 not covered with the fluororesin 8, and the porous region 3 is formed on the surface of the silicon substrate 1.
In this embodiment, when the current density is higher than 50 mA / cm ² , an etching effect occurs and the silicon substrate 1
The current density is preferably 50 mA / cm ² or less because the porous region 3 cannot be formed on the surface of the substrate.

In the present embodiment, the anodization is performed so that the thickness of the porous region 3 is about 1 μm. Note that the thickness of the porous region 3 means that the silicon substrate 1
Is the average of the depths from the surface.

When the thickness of the porous region 3 becomes about 1 μm or more, the crystalline silicon particles 4 existing 1 μm or more behind the hole 2 formed in the following steps emit light even if the silicon substrate 1 emits light. It does not reach the outside sufficiently and cannot contribute to light emission. Similarly, considering the case of a light receiving element, light received from outside the silicon substrate 1 does not sufficiently reach the crystalline silicon particles 4,
This is because it cannot contribute to light reception.

If the substrate is irradiated with light from a tungsten lamp to generate holes in the silicon substrate and anodize the substrate, an n-type silicon substrate can be used.

<Silicon Film Deposition Step> Next, using a high-frequency plasma CVD method, as shown in FIG.
An amorphous silicon film 5 is formed on the silicon substrate 1 by vapor deposition so as to have a thickness of about 3 nm to about 10 nm. Here, the film thickness of the silicon film 5 refers to FIG.
As shown in (c), the distance d from the surface of the silicon substrate 1 where the holes 2 are not formed to the surface of the silicon film 5.
Further, the substrate temperature of the silicon substrate 1 is set to about 100 ° C. to about 25 ° C.
An amorphous silicon film can be formed at a temperature of 0 ° C.

In this embodiment, the high-frequency plasma CV
The method D is used because the method is excellent in film formation with excellent step coverage.
This is because the silicon film 5 is buried in the hole 2.
Can be said to be a suitable method. In addition, when the silicon film 5 is formed,
The condition is that the gas pressure is about 10 ^-Four, Power supply frequency 13.5
6MHz, input power 300W, SiH_FourAnd H_TwoGas concentration
Degree ratio is SiH_Four: H_Two= 1: 10, silicon substrate 1 substrate
The test was performed at a temperature of about 100 ° C. Note that the gas pressure conditions
About 10^-Four~ About 10^-2Select a line as appropriate within the range of Pa
Just do it.

Although the silicon film 5 is formed so as to be in an amorphous state, it may be in a microcrystalline state. The silicon film 5 in the case of microcrystals has a substrate temperature of the silicon substrate 1 of about 30.
It can be obtained by setting the temperature to 0 ° C. Further, the thickness of the silicon film 5 can be appropriately adjusted by changing the film formation time.

<Heat Treatment Step> Next, as shown in FIG. 2D, the ohmic electrode 7 formed on the back surface of the silicon substrate 1 is once removed so that the ohmic electrode is not melted by heating. The ohmic electrode 7 made of aluminum is approximately 40
It can be removed by immersion in phosphoric acid at ℃. If not removed,
This is because the heating causes the ohmic electrode 7 to melt and fix the silicon substrate 1 and the pedestal supporting it.

Thereafter, the silicon substrate 1 on which the amorphous silicon film 5 is formed is subjected to a heat treatment. At this time, part of the silicon atoms in the amorphous silicon film 5 in the holes 2 and on the silicon substrate 1 is transformed into crystalline silicon particles 4 by heat, and the crystalline silicon particles 4 are scattered in the silicon film 5. Become. This phenomenon is caused by a variation in stabilization when silicon atoms having different inter-bond distances scattered in the amorphous silicon film are stabilized by heat.

The condition of the heat treatment is that the gas pressure is about 10 ^-6.
Pa, the rate of temperature rise is 50 ° C./second, the ambient temperature during the heat treatment is about 800 ° C., and the time of the heat treatment is 90 seconds. The heat treatment is preferably performed so that the gas pressure is in the range of about 10 ^-6 to about 10 ^-4 Pa and the ambient temperature during the heat treatment is in the range of about 700 to 900 ° C.

Next, an ohmic electrode 7 is again formed on the back surface of the silicon substrate 1 by EB vapor deposition of aluminum.

The diameter of the crystalline silicon particles 4 in the silicon film 5 generated in the heat treatment step ranges from about 1 nm to about 1 nm.
It was distributed at 0 nm and the average particle size was about 3.8 nm.

The silicon film 5 on the region of the silicon substrate 1 where the holes 2 are not formed (on the surface of the silicon substrate 1)
The diameter of the crystalline silicon particles 4 in the inside is about 1 nm to about 10 nm.
In order to achieve this, the thickness of the silicon film 5 should be about 3 nm to about 1 nm.
The thickness may be set to 0 nm. Note that the thickness of the silicon film 5 can be appropriately adjusted by changing the film formation time in the silicon film deposition step.

As in this embodiment, the diameter of the crystalline silicon particles 4 in the silicon film 5 on the surface of the silicon substrate 1 and the size of the holes 2
The particle size of the crystalline silicon particles 4 in the silicon film 5 in
It is desirable to distribute them to almost the same extent. This is because if the distribution varies, the luminous efficiency deteriorates.

<Electrode Deposition Step> Finally, as shown in FIG. 2E, a display electrode 6 made of translucent gold is formed on the silicon film 5 by vacuum deposition. Note that a transparent electrode of ITO or SnO ₂ may be used as the display electrode.

As described above, an optical functional element as a light emitting element or a light receiving element can be obtained.

Next, the relationship between the PL (photoluminescence) intensity and the heating temperature in the heat treatment step when the optical functional device manufactured in this embodiment emits light will be described with reference to FIG.

According to FIG. 4, the emission intensity increases in the range of about 700 ° C. to about 900 ° C., with the maximum when the heating temperature is 800 ° C., and the emission intensity decreases when the heating temperature is less than 700 ° C. It can also be seen that the emission intensity is low even when the temperature exceeds 900 ° C. This is 700
At a heating temperature lower than 900C or higher than 900C, it is considered that the crystalline silicon particles 4 generated by the denaturation of the silicon film 5 are small. The PL intensity was measured using a He-Cd laser having a wavelength of 325 nm and an output of 60 mW. The oscillation wavelength was 650 nm.

Next, the relationship between the EL (electroluminescence) intensity when current is injected into the light emitting device manufactured in the present embodiment and the current density required for light emission is as follows.
This will be described with reference to FIG.

As shown in FIG. 5, it can be seen that the light emitting device according to the present embodiment maintains linearity in the relationship between EL intensity and injected current density over a wide range. Also,
The light emitting device according to the present embodiment has a higher E than the conventional light emitting device.
It can be seen that the L intensity is increased, and it can be sufficiently used as a light emitting element.

[0045]

The feature of the optical functional device according to the present invention is that silicon, not a polymer material, is embedded in the pores of the porous region formed in the silicon substrate.

As a result, when current is injected, the efficiency of electron injection into the crystalline silicon particles in the hole can be increased. Conversely, when light is received, electrons and holes generated by optical coupling can be reduced. Mobility can be increased.

A feature of the method for manufacturing an optical functional device according to the present invention is that amorphous or microcrystalline silicon is formed in holes of a silicon substrate and the silicon substrate is heated.

As a result, a part of the amorphous or microcrystalline silicon formed in the hole of the silicon substrate can be transformed into crystalline silicon particles, and crystalline silicon particles contributing to light emission can be formed. It is possible to obtain an optical functional element having high light emission intensity or good light receiving sensitivity.

[Brief description of the drawings]

FIG. 1 is a sectional view of a light emitting device according to an embodiment of the present invention.

FIG. 2 is a process sectional view illustrating the method for manufacturing the light emitting device according to the embodiment of the present invention.

FIG. 3 is a sectional view schematically showing an anodizing apparatus.

FIG. 4 is a diagram showing the relationship between the photoluminescence intensity and the heat treatment temperature of the light emitting device according to the embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between EL intensity and current density of the light emitting device according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view of a conventional light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 101 Silicon substrate 2, 102 Hole 3, 103 Porous area 4 Crystal silicon particle 5 Silicon film 6, 106 Display electrode 7, 107 Ohmic electrode 8 Fluororesin 9 Constant current source 10 Platinum electrode 11 Tank 12 Solution 105 Carrier injection electrode

Claims (8)

[Claims] 1. An optical functional device comprising: a silicon substrate; a plurality of holes formed in the silicon substrate; crystalline silicon particles in the holes; and silicon filling the holes. 2. The optical functional device according to claim 1, wherein the particle diameter of the crystalline silicon particles is 1 nm or more and 10 nm or less. 3. The semiconductor device according to claim 1, further comprising silicon formed on a surface of the silicon substrate, wherein a thickness of the silicon on the surface of the silicon substrate is 3 nm or more and 10 nm or less. 3. The optical functional device according to 2. 4. A first step of forming a hole in a silicon substrate, a second step of forming amorphous or microcrystalline silicon in the hole, and a third step of heat-treating the silicon substrate. And a method for manufacturing an optical functional device. 5. The heating temperature in the third step is 7
The method for manufacturing an optical functional device according to claim 4, wherein the angle is from 00 ° to 900 °. 6. The method according to claim 4, wherein the first step is an anodizing treatment step. 7. The optical function device according to claim 5, wherein in the second step, amorphous or microcrystalline silicon is formed also on the surface of the silicon substrate. Manufacturing method. 8. A method for manufacturing an optical functional device, wherein the thickness of the silicon on the surface of the silicon substrate is 3 nm or more and 10 nm or less.