JPH02248037A - Formation of amorphous semiconductor - Google Patents

Abstract

PURPOSE:To make it possible to control arbitrarily the band gaps of amorphous semiconductor layers to be laminated by a method wherein the pulse width and the pulse period of a pulse-status electric field, which is applied in group IV element compound gas-containing raw gases, are changed. CONSTITUTION:Parallel plates (electrodes) 2 and 3 are installed opposing to each other in the interior of a vacuum tank 1 and a substrate 4 is put on the electrode 3. A pulse generating power supply 7 is connected to the electrode 2 and an RF high frequency or a DC electric field which is generated by the power supply 7 is modulated in a pulse status. In the case of a DC electric field, a pulse electric field of a width W is repeatedly applied at a period T and in the case of a high-frequency electric field, an RF electric field is applied in the interval only of the pulse width W. Group IV element compound gas- containing raw gases, such as SiH4 gas and CH4 gas, are introduced through a raw gas introducing tube 5 under a reduced pressure and a pulse width W and a period T of a field pulse are set corresponding to the initial band gap of an amorphous semiconductor layer to be formed. Thereby, amorphous semiconductor layers, whose band gaps are different from one another, can be easily formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an amorphous semiconductor having an arbitrary band gap by plasma CVD.

[Conventional technology]

For example, when a p-type amorphous silicon layer with a wide bandgap is brought into contact with an l-type amorphous silicon layer with a narrow bandgap as a window layer of a solar cell, or when an amorphous silicon thin film with a wide bandgap is brought into contact with a thin film of amorphous silicon with a narrow bandgap. When creating a superlattice structure by laminating amorphous silicon thin films, plasma CVD using RF high frequency or DC electric field is performed using different raw material gases, such as 5tne and C1+, and changing the mixing ratio of these gases. A method of obtaining amorphous silicon layers having different band gaps is known.

[Problem to be solved by the invention]

As mentioned above, in the method of changing the bandgap of an amorphous semiconductor produced by plasma CVD by changing the mixing ratio of raw material gases, it is possible to It is impossible to change the bandgap in In particular, when attempting to accurately create a superlattice structure in which layers are stacked by changing the bandgap intermittently, it is necessary to stop the -degree discharge, completely change the gas mixture ratio, and then start the discharge again. There are problems in that it takes time and many defects occur at the interface.

An object of the present invention is to provide a method for producing an amorphous semiconductor that can solve the above-mentioned problems and easily form amorphous semiconductor layers with different band gaps.

[Means to solve the problem]

To achieve the above object, the present invention applies an electric field in a pulsed manner when performing plasma CVD by applying an electric field to a source gas containing at least one Group 4 element compound gas to generate a glow discharge. However, the pulse width and pulse period of the pulse are set to correspond to the intended band gap of the amorphous semiconductor to be generated.

(Function) If the electric field applied to perform plasma CVD is pulsed, the electron temperature and plasma potential in the plasma will change in accordance with the pulse waveform.Therefore, the pulse waveform can freely control the electron temperature and plasma potential. By freely controlling the electron temperature and plasma potential, it is possible to control the reaction rate of raw materials in the plasma.Thereby, the amount of ions and radicals in the plasma can be controlled. I can do it.

Therefore, according to this method, an amorphous semiconductor can be produced by controlling the reaction rate of the gas by simply changing the pulse width and pulse period of the pulsed electric field without changing the composition of the source gas. The composition ratio can be changed and the band gap can be controlled.

〔Example〕

FIG. 1 shows the configuration of an apparatus used in an embodiment of the present invention. Inside a vacuum chamber 1, parallel plate electrodes 2.3 are installed facing each other.
A substrate 4 is placed on one electrode 3. A raw material gas introduction pipe 5 and a vacuum exhaust system 6 are connected to the vacuum chamber 1 . A pulse generating power supply is connected to the electrode 2 .

The RF high frequency or DC electric field generated by the pulsed power source is modulated in a pulsed manner. The second example of DC electric field modulation is
As shown in the figure, a pulsed electric field of width W is repeatedly applied with a period T. In the case of a high-frequency electric field, 13
．． A 56 MHz RF electric field is applied. Figure 3 shows the first
Using the device shown in the figure, 5 liters of raw material gas is introduced from the raw material gas inlet pipe 5 under reduced pressure.
Introducing le and CH4 and setting the pulse period T to 1000μ
The film quality of amorphous silicon carbide (a-3IC:II) obtained by varying the pulse width as sec is shown.
Pulse width W from 3μsec to 1000#aec (continuous)
By changing the optical bandgap E of a-3IC:H to 2. It changes from Ov to 1.75 eV, and the optical conductivity σ and h also change continuously.

FIG. 4 shows a superlattice structure formed using the apparatus shown in FIG.
Electric field with pulse width 1000 μsec and pulse width 3 μsec
The film is formed by alternately applying an electric field of, for example, every 30 seconds. When the pulse width is 1000 μ3 ec, continuous discharge occurs. This results in a-sic+g layers 13 each having a thickness of, for example, 20 bandgap E* 1-75 eV.
and E, 2. OeV (D a-3IC=II layer 14
were stacked to form a superlattice structure. Note that electrodes 15°1 are provided at the ends of the transparent conductive film 12 and on the top layer, respectively.
6 was established. In this way, a superlattice device such as a light emitting diode is formed. Of course, it is possible to freely change the size of the optical bandgap by changing the type of source gas and the initial setting of the flow rate ratio. Further, in the above embodiment, the pulse period T is 1000 μs.
ec, but depending on the type of gas, this may be changed to 0.2μ
By varying the pulse width between sec and 10 sec and freely varying the pulse width within that range, it is possible to freely control the film quality. Such superlattice structure amorphous semiconductors are used as materials for light emitting diodes.

FIG. 5 shows another embodiment of the present invention and is a band diagram of an amorphous silicon solar cell having a pin structure. In solar cells with a pin structure, the p layer on the light incident side, which is the so-called window layer, is made of a-3iC with a wide bandgap.
:H film is used to increase the light transmittance (in the known 0 diagram, two layers consisting of a-sic:a
1. 1J111n made of amorphous silicon (a-3i)
In addition to the pin structure composed of layer 23, two layers 21
An interface layer 24 is inserted between the first layer 220 and the second layer 220 . In this embodiment, the gradient of the bandgap of the interface layer therein is obtained by varying the pulse width of the pulsed electric field applied between the picture electrodes 2.3 of the device of FIG. Specifically, from the raw material gas introduction pipe 5, a flow rate of 200 SC (: 5iHe of M, 2 SCCM
CHI.

Using a mixed gas of 20 SCCM h as the source gas, setting the pulse period to 1 m5 ec, and changing the pulse width continuously from 3 μsec to 1000 μsec, which is a continuous discharge, over a period of 30 minutes, the band gap E was changed from 2 eV to 1. 7
The interface layer 24 was deposited to a thickness of 200 to 400 layers with the same bandgap as the second layer 21 on the one hand and the same bandgap as the first layer 22 on the other hand. By inserting the eighth layer 24, which is an interface whose bandgap changes smoothly, pM12
The built-in potential between the 1 and 0 layers 23 has increased, resulting in a higher output voltage.

The present invention is not limited to the above two embodiments, but can be implemented in all cases where it is necessary to control the band gap of an amorphous semiconductor produced by plasma CVD.

〔Effect of the invention〕

According to the present invention, the pulse period of the pulse power source applies voltage to the electrodes in the vacuum chamber of the plasma CVD apparatus without changing the raw material gas mixture ratio in the chamber.

By changing the pulse width, the bandgap of the laminated amorphous semiconductors can be arbitrarily controlled.

In particular, when stacking amorphous semiconductor films with different bandgaps for superlattice structures, solar cells, etc., there is no need to stop the discharge and fail to introduce gas, allowing film formation without time loss. , it is possible to prevent the occurrence of interface defects due to discharge stoppage.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a plasma CVD apparatus used in an embodiment of the present invention, FIG. 2 is a diagram of the output waveform of a pulsed power source, and FIG. 3 is the pulse width of the applied electric field at a pulse period of L m5ec and the resulting a-5IC: FIG. 4 is a cross-sectional view of a superlattice device obtained by one embodiment of the present invention, and FIG. 5 is an interface obtained by another embodiment of the present invention. This is a band diagram of a colon battery with layers. 1: Vacuum chamber, 2, 3: Electrode, 4: Substrate, 5: Raw material gas introduction tube, 6: Vacuum exhaust system, 7: Pulse power source. Figure 1 Figure 2 (Rus? I (usec) Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) When performing plasma CVD by applying an electric field to a raw material gas containing at least one Group 4 element or compound gas to generate a glow discharge, the electric field is applied in a pulsed manner, and the pulse width and pulse width of the pulse are A method for producing an amorphous semiconductor, characterized in that a period is set in accordance with a desired bandgap of the amorphous semiconductor to be produced.