# US 4,392,297 A · Process of making thin film high efficiency solar cells

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- Number: US 4,392,297 A
- Document ID: US4392297A
- Status: Granted
- Kind: A
- Application number: 06/390,172
- Filed: 1982-06-21
- Granted: 1983-07-12
- Earliest claimed: 1980-11-20
- Assignees: Spire Corporation
- Inventors: Roger G. Little
- Web page: https://patentgrep.com/patent/US4392297A

## CPC

- H10F 10/144: comprising only Group III-V materials, e.g. GaAs,AlGaAs, or InP photovoltaic cells
- H10F 71/00: Manufacture or treatment of devices covered by this subclass (patterning processes to connect thin photovoltaic cells in integrated devices, or assemblies of multiple devices, having photovoltaic cells H10F19/33; manufacture or treatment of encapsulations or containers for integrated devices, or assemblies of multiple devices, having photovoltaic cells H10F19/80; manufacture or treatment of integrated devices, or assemblies of multiple devices, comprising at least one element in which radiation controls the flow of current H10F39/00)
- H10F 71/127: {The active layers comprising only Group III-V materials, e.g. GaAs or InP}
- H10F 71/128: {Annealing}
- H10F 71/131: {Recrystallisation; Crystallization of amorphous or microcrystalline semiconductors}
- H10F 71/134: {Irradiation with electromagnetic or particle radiation}
- Y02E 10/544: Solar cells from Group III-V materials
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- Y10S 438/933: Germanium or silicon or Ge-Si on III-V
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

Process of making thin film materials for high efficiency solar cells on low-cost silicon substrates. The process comprises forming a low-cost silicon substrate, forming a graded transition region on the substrate and epitaxially growing a thin gallium arsenide film on the graded transition region. The process further includes doping the thin gallium arsenide film and forming a junction therein. The graded transition region preferably is a zone refined mixture of silicon and germanium characterized by a higher percentage of germanium at the surface of the region than adjacent the substrate. The process also includes the formation of homojunctions in thin gallium arsenide films. Solar cells made from the materials manufactured according to the process are characterized by a high conversion efficiency, improved stability and relatively low unit cost.

## Claims

### Claim 1

A process of forming a high efficiency single-crystal, thin film, homojunction gallium arsenide solar cell on a single-crystal silicon substrate comprising:
(a) forming a single-crystal silicon substrate;
(b) forming a graded transition region on said substrate by deposition of a thin layer of germanium directly on said silicon substrate and pulsing said layer with an electron beam to effectuate thereby zone refining and mixing of said germanium layer and said silicon substrate;
(c) epitaxially growing a thin gallium arsenide film on said transition region;
(d) doping said thin gallium arsenide film with one dopant species;
(e) forming a homojunction in said thin, doped gallium arsenide film by introducing therein a second dopant species; and
(f) forming front ohmic contacts on said gallium arsenide film.

### Claim 2 (depends on 1)

The process of claim 1 wherein said deposited thin layer of germanium is in the amorphous state.

### Claim 3 (depends on 2)

The process of claim 2 wherein said depositing said thin layer of germanium is effected by low-temperature chemical vapor deposition.

### Claim 4 (depends on 1)

The process of claim 1 wherein said depositing said thin layer of germanium is effected by evaporation.

### Claim 5 (depends on 4)

The process of claim 4 further including stitching the evaporated layer of germanium at selected points to said substrate by impinging high energy ions at said layer at said selected points.

### Claim 6 (depends on 1)

The process of claim 1 wherein said pulsing said layer of germanium causes a melting of said layer and of said silicon substrate at their interface, which molten interface upon cooling effects zone refining and mixing the germanium with the silicon in said transition region from said substrate toward the surface of said transition region.

### Claim 7 (depends on 6)

The process of claim 6 wherein said zone refining and mixing of the germanium with the silicon results in a higher percentage of germanium at said transition region surface than adjacent said silicon substrate.

### Claim 8 (depends on 1)

The process of claim 1 wherein said epitaxially growing and doping said thin gallium arsenide film, said forming said homojunction and said front ohmic contacts includes low-temperature pulsed electron beam processing.

### Claim 9

A process of forming a high efficiency single-crystal, thin film, homojunction gallium arsenide solar cell on a metallurgical grade silicon substrate comprising:
(a) forming a metallurgical grade silicon substrate;
(b) forming a graded transition region on said substrate by successive depositions of thin layers of germanium, with each of said layers being successively pulsed with an electron beam, causing thereby a melting of substantially equal thickness of said germanium layer and of said silicon substrate at their interface, which molten interface upon cooling effects zone refining and mixing of the germanium with the silicon in said transition region from said silicon substrate toward the surface of said transition region, said transition region comprising a mixture having a higher percentage of germanium at the surface of said transition region than adjacent said silicon substrate;
(c) epitaxially growing a thin gallium arsenide film on said transition region;
(d) doping said thin gallium arsenide film with one dopant species;
(e) forming a homojunction in said gallium arsenide film by introducing therein a second dopant species; and
(f) forming front contacts and a gallium-aluminum-arsenide window on said gallium arsenide film.