Higher current and higher voltage can be obtained by using Schottky barrier device with wide band-gap semiconductor as top layer and lower band-gap semiconductor underneath. Significant amount of solar radiation that is not absorbed by side band-gap material will be absorbed by narrow band-gap material

Stirn, R. J.

English

NASA Technical Reports Server

Semitransparent 
Metal Film 
n-GaAs 
(Narrow Band Gap)
nA lxGai xAs 
(Wide Band Gap) 
n+-GaAs 
(Substrate) 
Ohmic 
Contact 
June 1975	 B75-10125 
NASA TECH BRIEF 
•	 NASA Pasadena Office .	 A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Schottky Barrier Solar Cell Promises Improved Efficiency 
One of the major problems preventing the use of 
solar cells as a practical commercial energy source is 
their low efficiency (10 to .12 percent). A Schottky 
barrier photovoltaic cell [NASA Tech Brief B75-10119 
(NPO-13390)] is expected to have an efficiency of 
about 45 percent over the narrow wavelength for 
which it was developed. This suggested that such cells 
might be modified to serve as solar cells for solar 
energy-conversion systems.
However, Schottky barrier cells deliver power at a 
low voltage due to the limited band bending in the 
GaAs semiconductors. This can be overcome by using 
even wider band-gap semiconductors to provide 
increased barrier height and band bending. Unfortu-
nately, this leads to drops in current output because of 
the reduced solar absorption in the semiconductor. 
Both the low-voltage and low-current problems reduce 
the efficiency of the cell. 
Grid Contact	 Antireflection Coatina 
•
	
High-Voltage, High-Current Schottky Barrier Solar Cell
(continued overleaf) 
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Government assumes any liability resulting from the use of the 
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will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19750000125 2020-03-19T20:23:59+00:00Z
This apparent dilemma can be overcome using a 
Schottky barrier device with a multiple-layer struc-
ture. With a wide band-gap semiconductor as the top 
layer and a lower band-gap semiconductor under-
neath, both higher current and higher voltage can be 
obtained. A significant amount of the solar radiation 
that is not absorbed by the wide band-gap material 
will be absorbed by the narrow band-gap material. 
Thus the current output is enhanced, while the high 
voltage from the high barrier height is retained. 
The structure of the layered cell is shown in the 
figure. The thickness of the substrate n+-GaAs is 4 to 
8 mils (0.10 to 0.20 mm), and it is heavily doped to 
reduce series resistance and production costs. The 
n-GaAs and n-AlxGai..xAs layers are the narrower 
and wider band-gap layers, respectively. They are 
sequentially grown epitaxially on the substrate. The 
upper (n-AlxGaixAs) layer is several thousand 
angstroms thick (the order of iø mm), and the lower 
(n-GaAs) layer is several microns (the order of 10-3 
mm) thick. 
The top layer may also be any ternary compound 
having a good lattice match with GaAs and the 
required electrical characteristics. The semitranspar-
ent metal film thickness is 100 A (10-5 mm) or 
thinner. The contacts are a grid on the top surface 
and a metallic ohmic contact on the bottom of the 
substrate. The antireflection coating is applied over 
the metal film to reduce reflection losses.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: T5P75-10125 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning 
nonexclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Richard J. Stirn of
Caltech/JPL
under contract to

NASA Pasadena Office 
(NPO-13482)
. 
Categories: 03 (Physical Sciences) 
01 (Electronics - Components 
B75-10125	 and Circuitry)


Schottky barrier solar cell promises improved efficiency

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