Claims
- 1. A method of preparing an amorphous semiconductor which comprises pyrolytically decomposing one or more gaseous phase polysemiconductanes at a temperature below about 500.degree. C. and a partial pressure of said one or more polysemiconductanes in the range from above about 1 Torr to less than about 1 atmosphere.
- 2. The method of claim 1 wherein the pyrolytic decomposition takes place at a temperature in the range from about 300.degree. C. to about 500.degree. C.
- 3. The method of claim 2 wherein said temperature is in the range from about 350.degree. C. to about 450.degree. C.
- 4. The method of claim 1 wherein said partial pressure lies in the range from about one Torr to about 100 Torr, thereby to limit gas phase nucleation of particles.
- 5. The method of claim 1 wherein said polysemiconductanes are selected from the class ranging from disilanes to and including hexasilanes represented by the formula Si.sub.n H.sub.2n+2 where n ranges from two to six.
- 6. The method of claim 1 wherein said gaseous phase includes one or more dopant gases.
- 7. The method of claim 6 wherein said dopant gases are selected from the class including phosphorus and boron containing gases.
- 8. The method of claim 7 wherein said phosphorus containing gas is phosphine (PH.sub.3) and said boron containing gas is diborane (B.sub.2 H.sub.6).
SUMMARY OF THE INVENTION
This is a continuation-in-part of Ser. No. 242,707 filed Mar. 11, 1981, now abandoned.
Amorphous semiconductors are useful in a wide variety of devices. Examples include memories, field effect and thin film devices, displays and luminescent devices.
Amorphous semiconductors are particularly useful for photovoltaic devices which provide a voltage when subjected to radiation, or radiate when electrically energized. Unfortunately, photovoltaic devices are not presently competitive with conventional sources of electrical energy. This has been caused primarily by the cost of manufacturing suitable semiconductive materials. Initially, expensive and relatively thick single crystal material was required. More recently, amorphous material with suitable photosensitivity has been fabricated by glow discharge in a gaseous atmosphere.
Amorphous material in the form of hydrogenated silicon prepared by glow discharge has proved to be particularly suitable. Illustrations are found in U.S. Pat. Nos. 4,064,521; 4,142,195; 4,163,677; 4,196,438; 4,200,473 and 4,162,505.
Although the glow discharge manufacture of amorphous silicon is less costly than the production of single crystal material, cost considerations continue to limit the general employment of this technique.
One attempt to provide a lower cost material has involved the production of amorphous silicon by the pyrolytic decomposition of monosilane (SiH.sub.4). Other techniques employed with monosilanes have included sputtering and vacuum evaporation.
Unfortunately, the amorphous silicon produced by the pyrolytic decomposition of monosilane, commonly known as "chemical vapor deposition" (CVD) has shown limited photovoltaic or photoconductive behavior. This has continued to be the case even when the material is hydrogenated to compensate for what has been regarded as a defect density in the material.
Similarly, amorphous silicons prepared by sputtering and vacuum evaporation of monosilanes have exhibited less photoresponse than that provided by glow discharge materials.
Other attempts have been made to produce amorphous silicon from various fluorosilanes as described, for example, in U.S. Pat. Nos. 3,120,451 and 4,125,643. Here again, while the photoresponsive properties of the resultant materials have been similar to those associated with hydrogenated amorphous silicon produced by glow discharge, the costs of the process are still considerable.
Another method of preparing amorphous silicon is by the decomposition of silanes at a comparatively high temperature (1400.degree. C. to 1600.degree. C.) in a high vacuum reactor required to be held at pressure below 10.sup.-4 Torr. The resulting gas stream is then directed onto a substrate held at a lower temperature as set forth in U.S. Pat. Nos. 4,237,150 and 4,237,151. This technique is cumbersome, requires the use of high temperatures and high vacuums, and leads to films with rather low photoconductivities (10.sup.-7 (.OMEGA.-cm).sup.-1 or lower.)
Accordingly, it is an object of the invention to achieve the efficient and low cost production of semiconductive materials with suitable photoresponsive properties. A related object is to achieve suitable photovoltaic and photodetecting devices.
Another object of the invention is to provide for the production of semiconductive material with suitable photosensitivity with less cost and complexity than for single crystal materials.
A further object of the invention is to achieve amorphous silicon material at less cost and with less complexity than for glow discharge, sputtering and vacuum evaporation techniques.
In accomplishing the foregoing and related objects, the invention provides a method of preparing an amorphous semiconductor with suitable photosensitivity by the pyrolytic decomposition of one or more gaseous phase polysemiconductanes at a temperature below about 500.degree. C. This technique is to be distinguished from the prior art pyrolytic decomposition of silanes and fluorosilanes in which significantly lower photoconductivity and inferior photovoltaic properties have resulted. This procedure lends itself to continuous processing as opposed to batch processing, and eliminates the costly and complex equipment associated with the production of single crystals and amorphous silicon by glow discharge, sputtering and vacuum evaporation.
In accordance with one aspect of the invention, the decomposition takes place at a temperature in the range from about 300.degree. C. to about 500.degree. C. and is preferably in the range from about 350.degree. C. to 450.degree. C.
In accordance with another aspect of the invention, the decompositon takes place at a partial pressure of polysilane less than about one atmosphere and above about one micron of mercury, and preferably above about one Torr. A Torr is a unit of pressure equal to 1.333 millibars and one thousand microns of mercury at standard gravity and 0.degree. Centigrade. The pressure is desirably in the range from about one Torr to about 100 Torr in order to limit the gas phase nucleation of particles during pyrolytic decomposition. Gas phase nucleation is a showering of particles which leads to a mixture of amorphous and crystal materials.
In accordance with a further aspect of the invention, the polysemiconductanes are selected from the class ranging from disemiconductanes to and including hexasemiconductanes, represented by the formula Sc.sub.n H.sub.2n+2, where "Sc" refers to a semiconductor, such as silicon or germanium and n ranges from two to six. The polysemiconductanes are desirably obtained from the reaction product of a semiconductide, such as magnesium silicide (Mg.sub.2 Si) with a aqueous acid, such as phosphoric acid (H.sub.3 PO.sub.4), aqueous strong sulfuric acid (H.sub.2 SO.sub.4), hydrogen fluoride (HF) and hydrogen chloride (HCl). The semiconductanes of an order higher than disemiconductanes are separated by first passing the gaseous materials from the reaction chamber through a trap which is cooled by a mixture of solid and liquid toluene (-96.degree. C. ) which removes water and polysilanes of order higher than two. The resulting gaseous mixture is then passed through a trap cooled by a mixture of liquid and solid n-pentane (-136.degree. C.) which removes disilane. The gases which are not condensed in the trap (namely monosilane and hydrogen) are discarded. If higher purity disilane is desired, the disilane that has been trapped may be further purified by multiple traps to trap distillations, by low temperature fractionation, or by other procedures, such as gas chromatography, etc.
The polysemiconductanes may also be prepared by reduction of semiconductor halides, such as disilicon hexachloride with a hydride such as lithium aluminum hydride.
In accordance with a still further aspect of the invention the gaseous phase can include one or more dopant gases. The dopant gases are selected according to the conductivity type desired for the doped material. Suitable gases for doping include phosphine and diborane, according to whether the conductivity type is n or p.
In accordance with yet another aspect of the invention, the gaseous phase includes an inert gas carrier. Suitable inert gas carriers are argon, helium and hydrogen. The gas phase material is advantageously decomposed on a heated substrate and the decomposition temperature is that of the substrate.
In accordance with still another aspect of the invention, amorphous semiconductive devices are prepared by forming a body through the pyrolytic decomposition of one or more gaseous phase polysemiconductanes and providing contacts for the body. The body is desirably formed on a substrate in one or more separate layers which can include dopants according to the conductivity type desired. Auxiliary layers, such as metal to form an interface and antireflection layers, can be included.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
|
4237150 |
Wiesman |
Dec 1980 |
|
|
4237151 |
Strongin et al. |
Dec 1980 |
|
|
4357179 |
Adams et al. |
Nov 1982 |
|
Non-Patent Literature Citations (1)
| Entry |
| R. M. Plecenik et al., "Preparation of Amorphous Hydrogenated Silicon by Chemical Vapor Deposition", IBM Tech. Disc. Bull; vol. 24, 1523-1524 (1981). |
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
242707 |
Mar 1981 |
|
Patent Grant
4459163
