Nucleation and growth of crystalline films of silicon, germanium, and cadmium sulfide on substrates of plastic and glass were investigated. Amorphous films of germanium, silicon, and cadmium sulfide on amorphous substrates of glass and plastic were converted to the crystalline condition by electron bombardment

Evans, J. C., Jr.

English

NASA Technical Reports Server

December 1968	 Brie! 6-10556 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electron Beam Recrystallization of Amorphous Semiconductor Materials 
Semiconductor' films are readily formed on an 
amorphous substrate such as glass or plastic by 
evaporation or sputtering. The resulting Films, how-
ever, do not have the crystallinity required for elec-
tronic or photovoltaic device applications. In practice, 
the desired crystallinity can be obtained by maintain-
ing the substrate at an elevated temperature during the 
semiconductor deposition. One example of this ap-
proach is the deposition of cadmium sulfide onto a 
silver—zinc-coated polyimide sheet during the prep-
aration of thin-film solar cells. A similar accom-
plishment with higher melting semiconductors such as 
silicon or germanium has not been achieved because 
of the temperature limitations of available plastic 
substrates. 
It is known that for certain solid films the change 
from the amorphous condition to the crystalline in-
volves a reduction in the total energy content of the 
material. Part of this energy decrement is thought to 
be the release of strain energy. The ultimate state 
for such a solid film (i.e., the lowest energy condi-
tion) is a single crystal. One method of releasing 
strain energy, and thereby inducing crystallization, is 
by electron bombardment. The impinging electrons 
supply the small amount of activation energy neces-
sary to initiate the release of the strain energy. With 
electron bombardment techniques, the temperature 
rise experienced in the film during the onset of crystal-
lization is a fraction of that required to produce 
melting or sublimation. 
In this study, the nucleation and growth of crystal-
line films of silicon, germanium, and cadmium sulfide 
on substrates of plastic and glass were investigated. 
Amorphous films 800 to 300 angstroms (8x 10 to 
3x 10 /lm) thick of germanium, silicon, and cad-
mium sulfide on amorphous substrates of glass and 
plastic were converted to the crystalline condition by
electron bombardment. Two methods of electron 
bombardment were employed, namely, electron-beam 
raster scanning and general surface bombardment. 
The use of the electron-beam scanning technique to 
produce a predetermined pattern of crystalline regions 
in films of the semiconductor material deposited on 
the amorphous substrates was demonstrated. At 
electron-beam intensities which produce crystalliza-
tion of the films, no damage was noted to the plastic 
material immediately below the treated region. In 
separate tests, the vacuum decomposition temperature 
of the plastic material was found to be 250°C. 
Order-of-magnitude electrical-resistance measure-
ments were made on 500-angstrom- (5x l0jim-) 
thick silicon films before and after crystallization. 
A resistance decrease of four orders of magnitude 
was found. 
Note: 
Documentation for the innovation is available 
I roni:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: B68-10556 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
2 1000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10556 
Patent status: 
No patent action is contemplated by NASA. 
Source: John C. Evans. Jr. 
(LEW-10443) 
Category 02 
.. 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000512 2020-03-12T06:28:42+00:00Z



Electron beam recrystallization of amorphous semiconductor materials

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server