JPH0319694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amorphous semiconductor (AMORPHOUS SEMICNNDUCTOR).
By passing a current, especially a pulse current, to AS), this phenomenon is caused by rapid local heating of the area where carriers are recombined via the recombination center by the dangling bonds of the amorphous semiconductor. By activating the unpaired bond and bonding it with other nearby unpaired bonds or bonds neutralized with hydrogen, etc., the unpaired bond maintains a normal interatomic distance and cancels out the unpaired bond. This article concerns a method for manufacturing an amorphous semiconductor (AMORPHOUS SEMICONDUCTOR, or SAS).

The present invention physically generates reactions such as Si・+Si・→Si−Si Si・+Si・−H→Si−Si+H・ in a semiconductor such as silicon by applying an electric current, thereby reducing the density of dangling bonds. The purpose is to

Conventionally, AS has been defined by the fact that its interatomic distances are random and its crystallographic arrangement is also random.

Furthermore, due to its random nature, there were many dangling bonds in the AS that were not chemically bonded to others. This unpaired bond becomes the center of recombination and extremely shortens the lifetime of the carrier, making it the most anticipated carrier killer to eliminate. Recently, as a method for removing these dangling bonds, neutralization with hydrogen or halogen has been known. In other words, assuming that the semiconductor is silicon, Si.+H→Si-H Si.+F→Si-F. This is because films made using silane (SiH ₄ ), silicon tetrafluoride (SiF ₄ ), or a mixture thereof by glow discharge or plasma CVD have recombination centers of hydrogen and AS without the addition of halogens.
While the density of recombination centers is 10 ²⁰ to 10 ²² cm ^-3 , it is possible to reduce the density of recombination centers to 1/10 ⁴ to 10 ⁶ times that of 10 ¹⁷ to 10 ¹⁸ cm ^-3 . It is attracting attention as a thing.

However, such a density is not sufficient for a semiconductor, and therefore, when trying to make a photoelectric conversion device, especially a solar cell, the light-to-electricity conversion efficiency was 2 to 4%. The present invention brings the density of such recombination centers to 10 ¹³ to 10 ¹⁶ cm ^-3 and further to 1/10 ² to 1/10 ⁴ of that, closer to an ideal semiconductor, and as a result, the movement of electrons and holes is reduced. Degree of AS is 300Å
We were able to obtain values between 1 and 50 μm with an intermediate state of 10 ⁶ μm for CS and 10 6 μm. Examples thereof will be described below with reference to the drawings.

Example 1 In FIG. 1A, a conductor or semiconductor electrode 3 (hereinafter referred to as M), a semiconductor 1 (S or AS), and a conductor or semiconductor counter electrode 2 (hereinafter referred to as M) are formed on a substrate 4. A vertical cross-sectional view of the MSM structure is shown.

In the drawings, the semiconductor 1 is first coated with a silicide gas such as silane (SiH ₄ ), SiF ₄ , SiH ₂ Cl ₂ to a thickness of 0.1 to 10 μm using the glow discharge method or plasma CVD method.
In particular, it was formed to have a thickness of 1 to 2 μm. And 400~
Heated at a temperature of 600℃ and replaced the atmosphere with _H2 and He.
It turned into plasma when mixed with. Further, the film may be formed at a temperature 50 to 100°C lower than the crystallization temperature of 630 to 700°C.

Furthermore, before and after the process of forming this semiconductor, electrodes 3 and 2 made of a semiconductor doped with a large amount of metal or impurities are formed by vacuum evaporation or plasma CVD.
Alternatively, the structure shown in FIG. 1A was obtained by forming by low pressure CVD method.

Furthermore, pulse current was applied to these two electrodes in the range of 10 ² to ^{10 7} A/cm ² for ~100 seconds, especially from 0.1 to
Added for 2 seconds. If the electrode is a semiconductor, one side is P ⁺
One type or the other was made into N ⁺ type, and a current was applied thereto in the forward direction.

This current may be applied by charging a capacitor of 10 ² to 10 ⁵ PF, discharging it, and applying the current between the electrodes 3 and 2 multiple times.

Then, in the energy band diagram shown in FIG. 2, the electrons 5 flowing in the conduction band 8 and the holes 6 flowing in the valence band 9 recombine with each other via the recombination centers 7, ⁷¹ . However, at this time, the energy according to the energy band width is released as heat, and the temperature of this center line or its local vicinity increases, and the recombination center gains thermal energy from this heat. When this thermal energy is sufficient to bond the dangling bonds together, the two dangling bonds bond together and the interatomic distance is 2.
The most stable state for silicon atoms is 1.9 Å to 2.85 Å, 2.34 Å ± 20 Å, especially 2.3
~2.5 Å.

Another dangling bond and a neutralized atom, i.e., Si
When the thermal energy becomes larger than the bonding energy with -H, it becomes expressed as Si・+Si−H→Si−Si+H・, and this active hydrogen is neutralized by combining with other non-active dangling bonds. The conversion of H・+Si・→Si−H is carried out as shown in the following formula. As a result, it can be seen that this overcurrent can double cancel and neutralize the recombination center.

Also, when this cancellation/neutralization occurs, recombination at this part disappears, and the temperature of that part decreases, and electrons and holes recombine in the same way as each other via other recombination centers → heat generation → excitation of bond → Go through the process of neutralizing the bond. Therefore, by applying an electric current, the atomic arrangement of the semiconductor does not necessarily have a diamond structure and is indeterminate, but the distance between the atoms is the most stable state, that is, the interatomic distance is 2.34A + 0.2, which is the same as the distance in the crystalline state (2.34 Å). , -0.04A, which was found to be approximately homogeneous and constant.

In FIG. 3, the vertical axis represents the relative value of the density of the recombination center, and the initial value is defined as 1. Furthermore, when applying this current, intrinsic amorphous silicon has a conductivity of 10 ^-8 to ^{10 -12} cm ^-1 ,
This extremely low conductivity is not necessarily sufficient to conduct current. Therefore, in the present invention, the intrinsic semiconductor is irradiated with light with an intensity of 10 ³ LX or more using a xenon lamp, and electron-hole pairs are created and used to increase the conductivity to 10 ^-1 to 10 ^- It was improved to ⁶ cm ^-1 .

Then, apply voltage to two more electrodes to obtain 10 ²
A current in the range of ~5×10 ⁷ Acm ⁻² was applied. Also, this current density is 10 ³ A/cm ² in Figure 3.
(10), 10 ⁴ A/cm (11), 10 ⁵ A/cm ² (12),
10 ⁶ A/cm ² (13) for a predetermined period of time. Even though this current is a DC current, it is still 10ns to 1
It may be the total amount of current with a pulse width of ms. For pulse width, use a capacitor of 10 ² to ^{10 4} _pF .
The method of charging to 10 ⁴ V and discharging it may be repeated.

In addition, in this Figure 3, the substrate temperature is lower than room temperature.
At 200℃ and 300℃, room temperature graph 1 in Figure 3
2 and 13 could be obtained at low current densities of 10 ⁴ A/cm ² , respectively.

In practice, it was extremely effective to generate a photocarrier by light irradiation and to promote thermal excitation by heating when an electric current was applied, in order to apply an electric current without any problem.

This current density means the average current in this area. Since it refers to the current density in a region where the current flows locally under the electrode, it can be applied not only to a small area of 1 mm or less but also to a large area such as 10 ³ cm ² .

This figure 3 shows the case of amorphous silicon.
Ge, Ge _x Si _1-x (0<x<1), SiC _1-x (0<x<
1), Si ₁ N _4-x (0<x<4), SiO _2-x (0<x<2)
It goes without saying that compounds or mixtures such as these can be used in the same manner, and the term "semiconductor" as referred to in the present invention includes semi-insulators in the sense that current can flow therethrough.

Also, semiconductors are not only intrinsic, but also B, P,
Even if impurities such as As are added at a concentration of 10 ¹⁶ to 10 ²⁰ cm ^-3 to P-type or N-type, they also have a concentration of 10 ²¹ cm ^-3 to 10
It goes without saying that it may be a P or N type semiconductor added to a concentration of mol %.

Example 2 FIG. 1B shows an alternative construction embodiment.

Example 1 had the disadvantage that the irradiated light was partially blocked by the electrode 3 or 2.

FIG. 1B shows an arrangement in which light is irradiated from above onto a portion of the semiconductor 1 between the electrodes 2 and 3 using a Xe lamp. In this example, the thickness of the non-single crystal semiconductor was 2000 Å to 3 μm, the width was 1 to 10 mm, and the thickness was 10 to 100 mm.

The current density was 10 ² to 5×10 ⁶ A/cm ² , and the current value was gradually increased. In this way, the effect of light irradiation was fully utilized, so the reduction was 1/2 compared to Example 1.
Similarly, the density of recombination centers could be reduced to 1/10 ⁵ to 1/10 ⁴ at a current density of ~1/3.

When heating is performed at temperatures above 300℃ and below the crystallization temperature, the time required to reduce the density of recombination centers can be reduced by 1/2 to 1/10, and the current density can be reduced by 1/2 to 1/10.
It was possible to reduce the temperature to 10 to 10 ⁵ A/cm ² by about 1/3 for each 100°C increase.

However, in this case, the bond in the semiconductor that has a neutralization bond with hydrogen is also broken, and a new recombination center that generates heat is created. and helium (H ₂ 5-20%, He 80-95%)
Converts into plasma at ~100MHz or 1~10GHz,
It was preferable to perform plasma annealing in such an atmosphere. Therefore, the density of the recombination center is set to 400
It was 10 ¹⁵ - 10 ¹⁷ cm ^-3 at -600°C and could be further lowered to 10 ¹³ - 10 ¹⁵ cm ^-3 by hydrogenation neutralization.

Example 2 was the same as Example 1 except for the above. Thus, in silicon, where the carrier mobility is AS, it is only about 300 Å, but 1~
It has become ¹⁰³ times as large as 50μm.

Embodiment 3 FIG. 4 shows another embodiment of the present invention, in which the amorphous semiconductor of the present invention is applied to a photoelectric conversion device.

FIG. 4A shows a first electrode 24 on a substrate 4, an insulating or semi-insulating film 23 through which an M ₁ current, particularly a tunnel current, can flow, I ₁ , a semi-amorphous semiconductor 20, a second
An insulating or semi-insulating film 21, I ₂ , which can flow a current of
M ₁ consisting of a comb-shaped or grid-shaped second electrode M ₂
This is a photoelectric conversion device having a double MIS type structure of −I ₁ −SA−I ₂ −M ₂ . I ₁ and I ₂ are made of silicon nitride with a thickness of 10 to 40 Å by glow discharge or plasma CVD, and M ₁ is made of platinum with a work function of 4.0 eV or more.
The other second electrode _M2 is made of a transparent electrode such as chromium, nickel, gold or ITO, and the work function is
It was carried out using magnesium, aluminum, alkali metals, and alkaline earth metals with a voltage of 4.0 eV or less, and the two electrodes were complementary.

The semiconductor 20 has a reduced density of recombination centers according to Example 1 or 2. As a result, the conversion efficiency was dramatically improved to 7-10%. At this time, current was passed in the forward direction to the two electrodes, and in the drawing, light and/or infrared rays were irradiated from the top surface.

In FIG. 4B, a first electrode 24, a semiconductor 20, and a second electrode 21 are formed on a substrate 4, and the two electrodes and the semiconductor are in ohmic contact. The semiconductor 20 has a PIN junction consisting of a P ⁺ type layer 27, an intrinsic semiconductor 26, and an N ⁺ type semiconductor 23. Furthermore, a pulse current was passed in the forward direction as in FIG. 4A.

Thus, even with PIN type solar cells, the
It was possible to obtain a conversion efficiency of

In FIGS. 4A and 4B, the thickness of the semiconductor 20 is as thin as 1 to 5 μm, and a single crystal layer of 200 to 300 μm is not required due to direct transition due to lattice strain, and the carrier dispersion distance is 100 to 500 Å. It was estimated that the conversion efficiency could be improved 3 to 5 times because it has a diameter of 1 to 50 μm, unlike amorphous silicon.

The photoelectric conversion device is double MIS type or PIN
It is not limited to the type, but may be a structure with a large amount of PNPN...a modification of the PN structure, the shot structure, or the single MIS structure.

In the present invention, silicon is mainly described as the semiconductor. However, by adding oxygen, nitrogen, and carbon to silicon, SiO _2-x (0<X<2) and Si ₃ N _4-x (0<X<
4), Even if SiC ₂ (0<X<1), BP, GaAs,
Needless to say, the same applies to compound semiconductors such as GaAIAsInP.

Although the present invention has been described as an application to a photoelectric conversion device, the amorphous semiconductor of the present invention can also be applied to ICs such as semiconductor integrated circuits and insulated gate field effect transistors, LSIs, and VLSIs. Further, it can be applied to a copying machine such as a copying machine or an optical memory.

[Brief explanation of drawings]

FIG. 1 shows two cross-sectional views of an embodiment of the invention. FIG. 2 is an energy band diagram for explaining the theory of the present invention. FIG. 3 shows the reduction in recombination center reactions in the amorphous semiconductor obtained by the present invention. FIG. 4 shows an embodiment of a photoelectric conversion device to which the present invention is applied.

Claims (1)

[Claims] 1. An amorphous amorphous material characterized in that the density of dangling bonds or neutralized bonds is reduced by passing a current through a silicon-based semiconductor having an amorphous (amorphous) structure. Semiconductor manufacturing method. 2. The method for manufacturing an amorphous semiconductor according to claim 1, wherein the amorphous semiconductor has a conductivity type of P type, I type, or N type. 3. The method for manufacturing an amorphous semiconductor according to claim 1, wherein the current is a pulsed current. 4. The method for producing an amorphous semiconductor according to claim 1, characterized in that the amorphous semiconductor is heated to a temperature lower than the crystallization temperature before flowing an electric current. 5. The method for manufacturing an amorphous semiconductor according to claim 3, characterized in that the pulse current is applied for a period of 100 seconds or less at a temperature of room temperature to 600°C. 6. The method for producing an amorphous semiconductor according to claim 1, characterized in that carriers are generated by photoannealing or photoexcitation by applying light in parallel with passing a current.