Graduate Thesis Or Dissertation
 

Properties of flash-evaporated gallium arsenide and gallium phosphide epitaxial films

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  • The properties of flash- evaporated films of GaAs and GaP were studied in this investigation. Films were grown at various substrate temperatures, source temperatures, source-to-substrate distances and rates of deposition and were evaluated as to their structural, optical and electric properties. It was found that substrate temperature was the major factor in determining the crystallinity of the films. Films deposited below about 250°C were found to be amorphous. As the substrate temperature was increased, the crystallinity of the films improved. The optical data showed that the films had band gaps in the range of 1.34 to 1.72 ev. for GaAs films. Temperature-versus-resistivity measurements showed that the band gap for GaAs films varied from 1.18 ev. to 1.72 ev. The value for bulk GaAs is 1.47 ev. Films grown from evaporant powders obtained by crushing wafers of 6x10⁻³ ohm-cm to 0.01 ohm-cm material had very high resistivities. To lower film resistivity, additional doping was incorporated in the evaporant. Tin was added to n-type wafers and zinc to p-type wafers. The films grown from the tin-rich evaporant powders showed a decrease in resistivity for an increase in tin concentration and an increase in resistivity for a decrease in substrate temperature. Films grown from zinc-rich powders had high resistivities in all cases. Hall measurements were made but most films showed no voltage above the noise level of the measuring apparatus. The highest mobility value calculated from those films that exhibited Hall voltage was 0.7 cm²/volt-sec, far below the value of 8500 cm²/volt-sec for bulk GaAs. Electroluminescence was noted in high-resistivity GaP films grown on GaAs substrates. A wide spectral emission energy band was measured which would indicate an avalanche process as being the carrier injection mechanism. Point- contact and evaporated diodes were fabricated from the flash-evaporated films. Large leakage currents were noted in both types of diodes.
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file details MatsuoSamuelS1968_Redacted.pdf 2017-08-23 Pubblico Scaricare