Engineering topics

Olsen, Larry C.

Publications and source records attributed to Olsen, Larry C..

8 records

NASA NTRS1997

ZnSe Window Layers for GaAs and GaInP2 Solar Cells

This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

Olsen, Larry C.↗

NASA NTRS1995

ZnSe Window Layers for GaAs and GaInP2 Solar Cells

This report concerns studies of the use of ZnSe as a window layer for GaAs solar cells. Well-oriented crystalline ZnSe films on (100) single crystal GaAs substrates were grown by MOCVD. In particular, ZnSe films were grown by reacting a zinc adduct with hydrogen selenide at temperatures in the range of 200 C to 400 C. X-ray diffraction studies and images obtained with an atomic force microscope determined that the films were highly oriented but were polycrystalline. Particular emphasis was placed on the use of a substrate temperature of 350 C. Using iodine as a dopant, n-type ZnSe films with resistivities in the range of .01 to .05 ohm-cm were grown on semi-insulating GaAs. Thus procedures have been developed for investigating the utility of n-type ZnSe window layers on n/p GaAs structures. Studies of recombination at n-ZnSe/n-GaAs interfaces in n-ZnSe/n-GaAs/p-GaAs cell structures are planned for future work.

Olsen, Larry C.↗

NASA NTRS1993

Investigation of ZnSe-coated silicon substrates for GaAs solar cells

Studies are being carried out to determine the feasibility of using ZnSe as a buffer layer for GaAs solar cells grown on silicon. This study was motivated by reports in the literature indicating ZnSe films had been grown by metallorganic chemical vapor deposition (MOCVD) onto silicon with EPD values of 2 x 10(exp 5) cm(sup -2), even though the lattice mismatch between silicon and ZnSe is 4.16 percent. These results combined with the fact that ZnSe and GaAs are lattice matched to within 0.24 percent suggest that the prospects for growing high efficiency GaAs solar cells onto ZnSe-coated silicon are very good. Work to date has emphasized development of procedures for MOCVD growth of (100) ZnSe onto (100) silicon wafers, and subsequent growth of GaAs films on ZnSe/Si substrates. In order to grow high quality single crystal GaAs with a (100) orientation, which is desirable for solar cells, one must grow single crystal (100) ZnSe onto silicon substrates. A process for growth of (100) ZnSe was developed involving a two-step growth procedure at 450 C. Single crystal, (100) GaAs films were grown onto the (100) ZnSe/Si substrates at 610 C that are adherent and specular. Minority carrier diffusion lengths for the GaAs films grown on ZnSe/Si substrates were determined from photoresponse properties of Al/GaAs Schottky barriers. Diffusion lengths for n-type GaAs films are currently on the order of 0.3 microns compared to 2.0 microns for films grown simultaneously by homoepitaxy.

Huber, Daniel A.↗

NASA NTRS1993

Review of betavoltaic energy conversion

Betavoltaic energy conversion refers to the generation of power by coupling a beta source to a semiconductor junction device. The theory of betavoltaic energy conversion and some past studies of the subject are briefly reviewed. Calculations of limiting efficiencies for semiconductor cells versus bandgap are presented along with specific studies for Pm-147 and Ni-63 fueled devices. The approach used for fabricating Pm-147 fueled batteries by the author in the early 1970's is reviewed. Finally, the potential performance of advanced betavoltaic power sources is considered.

Olsen, Larry C.↗

NASA NTRS1991

GaAs solar cells for laser power beaming

Efforts to develop GaAs solar cells for coupling to laser beams in the wavelength range of 800 to 840 nm are described. This work was motivated primarily by interests in space-tp-space power beaming applications. In particular, the Battelle Pacific Northwest Laboratories is conducting studies of the utilization of power beaming for several future space missions. Modeling calculations of GaAs cell performance were carried out using PC-1D to determine an appropriate design for a p/n cell structure. Epitaxial wafers were grown by MOCVD and cells fabricated at WSU Tri-Cities. Under simulated conditions, an efficiency of 53 percent was achieved for a cell coupled to 806 nm light at 400 mW/sq cm.

Olsen, Larry C.↗

NASA NTRS1989

Investigation of high efficiency GaAs solar cells

Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

Olsen, Larry C.↗

NASA NTRS1987

Electro-optical characterization of GaAs solar cells

The electro-optical characterization of gallium arsenide p/n solar cells is discussed. The objective is to identify and understand basic mechanisms which limit the performance of high efficiency gallium arsenide solar cells. The approach involves conducting photoresponse and temperature dependent current-voltage measurements, and interpretation of the data in terms of theory to determine key device parameters. Depth concentration profiles are also utilized in formulating a model to explain device performance.

Olsen, Larry C.↗

NASA NTRS1985

Measurement and analysis of solar cell current-voltage characteristics

Approaches to measurement and analysis of solar cell current-voltage characteristics under dark and illuminated conditions are discussed. Measurements are taken with a computer based data acquisition system for temperatures in the range of -100 to +100 C. In the fitting procedure, the various I(oi) and C(i) as well as R(S) and R(SH) are determined. Application to current-voltage analyses of high efficiency silicon cells and Boeing CdS/CuInSe2 are discussed. In silicon MINP cells, it is found that at low voltages a tunneling mechanism is dominant, while at larger voltages the I-V characteristics are usually dominated by emitter recombination. In the case of Boeing cells, a current transport model based on a tunneling mechanism and interface recombination acting in series has been developed as a result of I-V analyses.

Olsen, Larry C.↗