JPH06349744A - Manufacture of superlattice structure - Google Patents

Abstract

PURPOSE:To easily manufacture a homogeneous supperlattice structure composed of the periodic structure of amorphous semiconductors having a large band gap difference between them. CONSTITUTION:In the plasma CVD method which is used for manufacturing an amorphous thin film on a substrate 109 by decomposing a gaseous starting material by impressing an electric field across an electrode 103 and the substrate 109 from a power source 101, a homogeneous supperlattice structure is formed on the substrate 109 by alternately introducing mixed gases prepared by mixing a rare gas and the gaseous starting gas at different mixing ratios into a vacuum vessel 102. For example, an i-type a-Si:H (B) layer is formed to a thickness of 20-100Angstrom by introducing SiH4. diluted with He to a concentration of 0.5-10vol.% into the vessel 102 and impressing high-frequency power upon the electrode 103 after an i-type a-Si:H (A) layer having a thickness of 20-100Angstrom is formed as a barrier layer by introducing SiH4 diluted with He to a concentration of 100-500ppm into the vessel 102 and impressing high-frequency power upon the electrode 103. A laminated body of the layers is obtained by repeating the abovementioned operations.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a light emitting element, a light receiving element,
The present invention relates to a method of manufacturing a superlattice structure applied to devices such as transistors.

[0002]

2. Description of the Related Art Superlattice structures are mainly composed of GaAs and GaAl.
It is manufactured using III-V group semiconductors such as As,
Light-emitting diode and laser diode using quantum size effect
Light emission efficiency of the device and high-speed response of the transistor
Or increase the carrier using the energy difference at the band edge.
Higher sensitivity of the light receiving element has been realized by doubling. On the other hand, large
It has the characteristics that it is easy to form an area and is highly workable.
Hydrogenated amorphous silicon (hereinafter abbreviated as a-Si: H)
Even in an amorphous semiconductor typified by
Have been attempted. Superlattice using amorphous semiconductor
The structure is a-Si: H and silicon nitride (hereinafter, Si_1-x
N_xIs abbreviated. However, 0 <x <1, and so on. ), A
-Si: H and hydrogenated amorphous silicon carbide (hereinafter,
a-Si_1-xC _x: H is abbreviated. ), Hydrogenated amorphous silicon
Recon germanium (hereinafter a-Si_{1- x}Ge_x: H and
(Abbreviated) and a different material such as a-Si: H
It is common to use a heterojunction. like this
The method of constructing a superlattice structure by heterojunction is easily prohibited
Since it is possible to realize combinations with widely different body widths, III
Most commonly used as well as -V semiconductors. Also,
Hydrogenated amorphous semiconductors have a prohibited range depending on the hydrogen content.
It has a characteristic that can change
A large size not available in conventional semiconductor materials that can form a child structure
It has certain characteristics.

[0003]

As a method for producing a hydrogenated amorphous semiconductor, plasma CVD (chemical vapor deposition method) is usually used. In the case of manufacturing a superlattice structure by heterojunction in which different materials are combined by this method, for example, a-Si: H and a-Si _1-x C _x : H will be described below as an example. First, SiH ₄ and a diluent gas are introduced into a vacuum container to produce an a-Si: H film on a substrate, and subsequently SiH ₄ and a diluent gas are mixed with CH ₄ and C _2.
H ₂ is introduced to stack an a-Si _1-x C _x : H film. Next, after evacuating the inside of the vacuum container so that CH ₄ and C ₂ H ₂ do not remain, SiH ₄ is introduced into the vacuum container and an a-Si: H film is further laminated as before. By repeating such an operation, a superlattice structure in which an a-Si: H film and an a-Si1 _{- xCx} : H film are periodically laminated is manufactured. Here, the diluting gas is used to enhance the stability of plasma, and hydrogen, He, Ar or the like is usually used. In order to form a heterojunction in this way, at least three types of gas introduction systems are required, and sufficient exhaust must be performed so that no gas remains during the formation of each layer. In addition, since compounds such as a-Si _1-x C _x : H and Si _1-x N _x contain more defects such as carrier traps and recombination centers than a-Si: H, they form a superlattice structure. However, there was a problem that the effect could not be brought out sufficiently. On the other hand, since the homogeneous superlattice is composed of the same material, it does not have the problem of the heterojunction superlattice. But,
In the production of a homogenous superlattice structure, for example, in a-Si: H by the plasma CVD method, the heating temperature of the substrate is raised or lowered in order to change the hydrogen content, and the wide and narrow bars are alternately stacked. However, there is a problem that it is difficult to make a structure with a large difference in the width of the prohibition body, because the width of the prohibition body is about 1.9 eV when the width is wide and only about 1.7 eV when the width is narrow. It was Further, in the reactive sputtering method, the hydrogen content in the film can be changed by changing the partial pressure of hydrogen in the sputtering atmosphere, and the film having a narrow forbidden width of about 1.6 eV containing no hydrogen. It is possible to form a wide film of 1.9 eV containing a large amount of hydrogen and hydrogen, but defects due to ion bombardment in the film are plasma C
Compared with the VD film, the effect could not be realized even if a superlattice structure was formed.

The present invention is to solve the above-mentioned conventional problems and has a large difference in the width of the prohibited body.
Moreover, it is an object of the present invention to provide a method for easily producing a homogenous superlattice structure which has no defects and realizes the original operation of the superlattice by using the plasma CVD method.

[0005]

A method of manufacturing a superlattice structure according to the present invention for achieving the above object comprises at least one element selected from silicon, carbon and germanium (hereinafter,
These elements are collectively described as X), and
In the method for manufacturing a superlattice structure in which amorphous semiconductor layers containing hydrogen are alternately formed, a compound gas containing at least the X atoms and hydrogen atoms and a mixed gas having different rare gas mixing ratios are alternately placed in a vacuum container. And discharging an electric field by applying an electric field to the mixed gas to decompose the compound gas and form the superlattice structure on the substrate arranged in the vacuum container.

In the above structure, the difference in the width of the prohibited body is 0.
A superlattice structure in which amorphous semiconductor layers of 3 eV or more are alternately formed is preferable. In the above configuration, X
A superlattice structure in which layers having more XH ₂ bonds than H bonds and layers having more XH bonds than XH ₂ bonds are alternately formed is preferable.

Further, in the above construction, while the mixed gases having different mixing ratios are alternately introduced into the vacuum container,
It is preferable to alternately change the heating temperature of the substrate.

[0008]

According to the structure of the present invention, at least the X
A compound gas consisting of atoms and hydrogen atoms and a mixed gas having a different mixing ratio of a rare gas are alternately introduced into a vacuum container, an electric field is applied to the mixed gas to generate a discharge, and the compound gas is decomposed to decompose the compound gas. By forming the superlattice structure on a substrate placed in a vacuum container, a homogenous superlattice structure that has a large difference in forbidden body width and has no defects and realizes the original operation of the superlattice is formed by plasma CVD. It can be easily manufactured using the method. That is, He and A
Consider a case where SiH ₄ diluted with a rare gas such as r is used to form an a-Si: H film using the plasma CVD method. In plasma, SiH ₄ is an intermediate species SiH, SiH ₂ , SiH
Dissociated into _3, etc. The a-Si: H film is formed by the diffusion of these intermediate species onto the substrate and the adsorption reaction on the surface. Therefore, the bonding state of silicon atoms and hydrogen atoms and the hydrogen content in the film strongly depend on the state of the intermediate species contributing to the film formation and the state of the substrate surface. It is known that the surface material is mainly SiH ₂ or SiH ₃ having a long life. Therefore, when the degree of dilution with a rare gas is largely changed from the% order to the PPM order, the intermediate reaction that contributes to film formation due to the change of the secondary reaction in the gas phase due to the decrease of the concentration of the intermediate species and the electron temperature change in the plasma. The type of species also changes greatly. Therefore, by diluting SiH ₄ with a rare gas, and by alternately introducing gases having greatly different concentrations into the plasma, the hydrogen bond state and the hydrogen content greatly differ (in other words, the forbidden band width largely differs). The a-Si: H films are alternately laminated.
As a result, a homogenous superlattice structure can be easily manufactured.

[0009]

EXAMPLE A superlattice structure manufactured by the method for manufacturing a superlattice structure according to the present invention has an amorphous thin film of a-Si whose bandgap can be largely changed by changing the hydrogen content and the hydrogen bonding state: H, a-Ge: H or a-C:
Constructed using H. In addition, these amorphous thin films are
Halogen atoms such as fluorine and chlorine may be contained in order to terminate dangling bonds in the film and enhance the carrier transport ability of electrons and holes.

Raw materials used for producing the above-mentioned amorphous thin film
The gas acts to terminate the dangling bond in the gas molecule.
It is necessary to include a hydrogen atom that has a
Specifically, SiH for the production of a-Si: H film_Four, Si₂
H₆, Si₃H₈, SiH_{Four- n}F_n, SiH_4-nCl_n
(However, n = 1,2,3) or other silicon compound gas, a-
C: CH for H film production_Four, C₂H₆, C₃H₈，
C₂H_Four, C₂H₂, C ₆H₆, CH_4-nF_n(However,
n = 1,2,3) etc. for carbon compound gas, for a-Ge: H film production
Then GeH_Four, Ge₂H₆, GeH_4-nF_n(However,
n = 1,2,3,4) and use these gases as He, Ne, A
Dilute with a rare gas such as r, Kr, or Xe. Diluted mixture
The value of the concentration of the raw material gas in the gas is 100 ppm to
The range of 50 vol.% Is desirable. Because 100ppm
If the concentration is less than 100%, the purity of the rare gas will be a problem and impurities in the film will be impure.
It is not desirable because mixing of things can not be ignored, 50 vo
If the concentration exceeds l.%, the pressure change due to decomposition of the raw material gas
Is not preferable because the stability of the plasma decreases due to movement.
Because. In addition, changing the electrical conductivity of the amorphous thin film
Therefore, in the case of n-type conduction, impurities such as P and As are contained in the film.
PH₃, AsH₃May be added using gas such as,
In the case of p-type conduction, impurities of B and Ga are added to B₂H₆, B
F₃, Ga (CH₃)₃Even if added using gas such as
Good.

The superlattice structure is manufactured by introducing the above mixed gas into a plasma CVD apparatus as shown in FIG. Power supply 101 is DC or high frequency (1kHz to 100MH
z) or a microwave (1 GHz or more) power supply, which is connected to the electrode 103 in the vacuum container 102 via a matching circuit 104 (however, in the case of direct current, the matching circuit 104 is unnecessary). Electrode 103 There are many holes in the shape of a shower,
The raw material gas and the rare gas from the raw material gas cylinder 105 and the rare gas cylinder 106 are adjusted to a predetermined flow rate by the mass flow controllers 107 and 108, and the vacuum container is supplied from these holes.
Introduced in 102. Substrate 109 forming superlattice structure
Is placed on the heater 110 and heated to a predetermined temperature. The manufacturing procedure of the superlattice structure will be described below. First, a mixed gas having a source gas concentration in a vacuum container 102 evacuated to a high vacuum is introduced, and a vacuum pump 111 and a valve 112 are used to adjust the pressure to a predetermined pressure.
An electric field is applied between 109 to generate plasma to form an amorphous thin film A having a predetermined thickness on the substrate 109. Subsequently, another mixed gas having a different source gas concentration is introduced into the vacuum vessel 102 and adjusted to have a predetermined pressure, and then plasma is generated in the same manner as before to form an amorphous film having a predetermined film thickness on the substrate 109. The quality thin film B is laminated. By repeating this operation alternately, amorphous thin films A and B having greatly different forbidden band widths are alternately laminated to manufacture a superlattice structure. Further, when the source gas concentration is changed and the heating temperature of the substrate 109 is also changed at the time of manufacturing the superlattice structure, the bandgap difference is further increased, and a high-quality low-defect superlattice structure can be manufactured.

In the case of FIG. 1, the mass flow controller-10
7,108 is used to control the flow rate of raw material gas and rare gas,
Although a mixed gas having two kinds of mixed gas ratios was prepared, two kinds of gas cylinders adjusted in advance to a predetermined mixed gas ratio may be used instead of the raw material gas cylinder 105 and the rare gas cylinder 106.

A specific embodiment will be described below. Example 1 A pin diode 202 using a superlattice for an i layer 201 as shown in FIG. 2 was manufactured using the plasma CVD apparatus shown in FIG. The superlattice part of the i layer is a wide band gap (A) layer
203 and the narrow (B) layer 204 are alternately laminated.
The pin diode 202 was manufactured as follows. First, as the transparent conductive electrode 205, a transparent insulating substrate 206 such as glass or quartz on which ITO or SnO ₂ is formed is placed in the vacuum container 102, and 150 to 25
Heated to 0 ° C. Then, after evacuating to below 10 ^-6 Torr, SiH diluted with He to a concentration of 0.5 to 10 vol.
₄ and 500-2000 PPM concentration of B ₂ H ₆ in a vacuum vessel 102
Introduced into the inside, under pressure of 0.4 ~ 1.0 Torr 13.56
Applying high frequency power of 10 MHz at 10 MHz to the electrode 103, p
As the layer 207, a p-type a-Si: H layer having a thickness of 200 to 1000 angstrom was formed. Then, the inside of the vacuum vessel 102 is evacuated to 10 ⁻⁶ Torr or less, the temperature of the substrate 206 is set to 50 to 150 ° C., and the He concentration is set to 0.5 to 10 vol.%.
SiH ₄ diluted with is introduced, and high frequency power of 10.56 MHz and 10 to 30 W is applied to the electrode 103 under a pressure of 0.4 to 1.0 Torr to form the i-type a-Si: H (B) layer 204 of 20 to 20. It was formed to a thickness of 100 Å. Further, after evacuating the inside of the vacuum container 102 to 10 ⁻⁶ Torr or less,
SiH ₄ diluted with He was introduced to a concentration of 100 to 500 PPM, and 13.56 MH under a pressure of 0.4 to 1.0 Torr.
Applying high frequency power of z, 10 to 30 W to the electrode 103, i
A mold a-Si: H (A) layer 203 was formed with a thickness of 20 to 100 angstroms. By repeating this operation, the i-type a-Si: H (B) layer 204 / i-type a-Si: H having 10 cycles
(A) Layer 203 An i layer 201 having a superlattice structure was manufactured.
Next, after the inside of the vacuum container 102 is evacuated to 10 ⁻⁶ Torr or less, the temperature of the substrate 206 is set to 150 to 250 ° C. and 0.5
SiH ₄ and 500 diluted with He to a concentration of ~ 10 vol.%
The PH ₃ of ~2000PPM concentration is introduced into a vacuum vessel 102,
13.56 MHz, 10 under pressure of 0.4 to 1.0 Torr
A high frequency power of W was applied to the electrode 103 to form an n-type a-Si: H layer as the n layer 208 with a thickness of 200 to 1000 angstroms. Then, cool the substrate 206 to room temperature,
The inside of the vacuum container 102 was evacuated to 10 ⁻⁶ Torr or less, and then leaked to take out the substrate 206. Next, a 3000 Å thick Al thin film is formed as a conductive electrode 209 on the n layer 208 by vacuum deposition to form a pin diode 202.
Was manufactured.

Separately, an i-type a-Si: H (A) layer
When 203 and the i-type a-Si: H (B) layer 204 were individually manufactured and evaluated, respectively, i-type a-Si: H (A) was obtained.
Layer 203 is 2.2 ～2.4EV optical forbidden band width, the absorption coefficient ratio alpha (2090) in the infrared absorption in the spectrum 2090 cm ^-1 and 2000cm ^-1 / α (2000) 2 to 4 and SiH bond Compared to S
It was found that iH ₂ binding was abundant in the membrane. Also,
The hydrogen content was 25 to 35 atomic%. On the other hand, i-type a
The optical bandgap of the --Si: H (B) layer 204 is 1.7 to 1.
8eV, α (2090) / α (2000) was 0.4 to 0.6, indicating that SiH bonds were more abundant in the film than SiH ₂ bonds. The hydrogen content was 12 to 18 atomic%. Therefore, the i layer 201 including the A layer 203 and the B layer 204 has a
It was found to be a homogenous superlattice structure with an energy difference of 5 to 0.7 eV.

This element 202 should be forward biased
When a half-wave rectified voltage of 100 to 1000 Hz is applied, 650
Visible light emission with a center wavelength of ~ 800 nm was obtained, and it could be operated as a light emitting diode.

Example 2 In the pin diode 202 manufactured in Example 1, the i layer
A light emitting diode 202 was manufactured in which the superlattice portion of 201 was formed of aC: H.

The manufacture of this diode 202 is as follows.
I went to. First, the ITO transparent conductive electrode 205 is formed
The glass substrate 206 thus prepared is placed in the vacuum vessel 102, and
Heat to ~ 250 ° C. Then 10^-6True below Torr
After emptying, it was diluted with He to a concentration of 0.5-10 vol.%.
SiH_FourAnd B of 500 to 2000 PPM concentration₂H₆The vacuum
It is introduced into the container 102, and under the pressure of 0.4 to 1.0 Torr, 1
Apply high frequency power of 3.56MHz, 10W to electrode 103
Then, a p-type a-Si: H layer of 200 to 1 is formed as the p layer 207.
It was formed to a thickness of 000 angstroms. Then, vacuum volume
10 in the container 102 ^-6After evacuating to less than Torr, the substrate
The temperature of 206 is 100-200 ℃, and 0.5-10vol.% Of
C diluted with He to a concentration₂H₂Introduced 0.4 to 1.0 T
13.56MHz, 10 ~ 30W high under the pressure of orr
I-type aC: H (B) by applying frequency power to the electrode 103.
Layer 204 was formed 20-100 Angstroms thick.
Furthermore, the inside of the vacuum container 102 is^-6Vacuum exhaust to below Torr
Then diluted with He to a concentration of 100-500 PPM C₂
H₂And 13.5 at a pressure of 0.4 to 1.0 Torr.
Apply high frequency power of 6MHz, 10 ~ 30W to electrode 103
Then, the i-type aC: H (A) layer 203 is turned on at 20 to 100 angstroms.
It was formed with a strom thickness. Repeat this operation for 10 laps
Phase i-type aC: H (B) layer 204 / i-type aC: H
(A) Layer 203 An i layer 201 having a superlattice structure was manufactured.
Next, the inside of the vacuum container 102 is set to 10^-6Vacuum exhaust to below Torr
After that, the temperature of the substrate 206 is set to 150 to 250 ° C.
SiH diluted with He to a concentration of ~ 10 vol.%_FourAnd 500
~ 2000PPM PH₃Is introduced into the vacuum container 102,
13.56 MHz, 10 under pressure of 0.4 to 1.0 Torr
A high frequency power of W is applied to the electrode 103 to form the n layer 208.
n-type a-Si: H layer 200-1000 angstrom
It was formed thick. Then, cool the substrate 206 to room temperature,
10 in the vacuum vessel 102^-6Evacuated below Torr
After that, the substrate 206 leaked and the substrate 206 was taken out. Next, the conductive charge
Vacuum 3000 Angstrom Al thin film as pole 209
A pin diode 20 is formed on the n layer 208 by vapor deposition.
Manufactured 2.

Apart from this, the i-type aC: H (A) layer 20
3 and i-type aC: H (B) layer 204 were individually manufactured and evaluated, and i-type aC: H (A) layer 203 was obtained.
In the optical bandgap is 2.5 ~3.0eV, absorption coefficient ratio of the red in the infrared absorption spectrum 2900 cm ^-1 and 880 cm ^-1 α (2
900) / α (880) was 5 to 10, and it was found that CH ₂ and CH ₃ bonds were more abundant in the film than CH bonds. On the other hand, the i-type aC: H (B) layer 204 has an optical bandgap
2.0 to 2.3 eV, α (2900) / α (880) 0.4 to 1 and CH ₂
It was found that CH bonds were more abundant in the membrane compared to and CH ₃ bonds. Therefore, it was proved that the i-layer 201 composed of the A layer 203 and the B layer 204 had a homogenous superlattice structure having an energy difference of 0.5 to 0.7 eV.

This element 202 should be forward biased
When a half-wave rectified voltage of 100 to 1000 Hz is applied, 450
Visible light emission with a central wavelength of ~ 600 nm was obtained, and it could be operated as a light emitting diode.

Example 3 In the pin diode 202 manufactured in Example 1, i
The superlattice structure of the layer 201 is replaced with a superlattice structure of i-type a-Si: H (A) layer 203 of 150 angstrom thickness i-type a-Si: H (B) layer 204/100 angstrom thickness of 30 periods. Avalanche photodiode 202 was manufactured. In this diode 202, from the p-layer side, 500-65
When the monochromatic light of 0 nm was irradiated and the photocurrent was measured, it was found that the quantum efficiency was 3 to 10. For comparison, the quantum efficiency was 1 when the photocurrent was also measured for the diode formed only by the i-type a-Si: H (B) layer 204 having a thickness of 7500 angstroms instead of the i-layer 201 having a superlattice structure. there were.

Example 4 In the pin photodiode 202 manufactured in Example 3, the i-type a-Si: H (B) layer 204 of the i layer 201 is a region for accelerating carriers. Therefore, i-type a-S
i: In order to increase the carrier mobility of the H (B) layer 204 and further reduce the density of dangling bonds, i:
The substrate temperature at the time of manufacturing the mold a-Si: H (B) layer 204 is set to 20.
An avalanche photodiode 202 having a temperature of 0 to 250 ° C. and a substrate temperature of 50 to 150 ° C. at the time of manufacturing the i-type a-Si: H (A) layer 203 was manufactured.

When the photocurrent of this device was measured in the same manner as in Example 3, it was found that the quantum efficiency was 5 to 20.

[0023]

According to the present invention, it is possible to easily manufacture a homogenous superlattice structure having a large band gap difference.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a plasma CVD apparatus used in an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a superlattice device manufactured according to an embodiment of the present invention.

[Explanation of symbols]

 101 Power supply 102 Vacuum container 103 Electrode 104 Matching circuit 105 Raw material gas cylinder 106 Rare gas cylinder 107,108 Mass flow controller 109 Base material 110 Heater 111 Vacuum pump 112 Valve 201 i layer 202 pin diode 203 Wide band gap (A) layer 204 Small band gap (B) layer 205 transparent conductive electrode 206 transparent insulating substrate 207 p layer 208 n layer 209 conductive electrode

Claims (4)

[Claims] 1. A method for producing a superlattice structure, which comprises at least one amorphous semiconductor layer containing hydrogen as a main component and containing at least one element selected from silicon, carbon, and germanium as a main component, wherein at least the silicon carbon and germanium are used. A compound gas containing at least one element selected as a main component and a mixed gas having a different mixing ratio of a rare gas are alternately introduced into a vacuum container, and an electric field is applied to the mixed gas to generate a discharge. Is formed and the superlattice structure is formed on a substrate arranged in the vacuum container. 2. The method for producing a superlattice structure according to claim 1, wherein the superlattice structure is formed by alternately forming amorphous semiconductor layers having a forbidden body width difference of 0.3 eV or more. 3. Selected from silicon, carbon and germanium.
At least one element (hereinafter abbreviated as X) that is released is hydrogen.
Bound to (H), compared to XH binding to XH ₂Combined
XH with many layers₂Alternating layers with more XH bonds than bonds
The superlattice structure according to claim 1, which is a superlattice structure formed in
Manufacturing method. 4. The method for producing a superlattice structure according to claim 1, wherein mixed gases having different mixing ratios are alternately introduced into the vacuum container and the heating temperature of the substrate is alternately changed.