Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Abstract

A vacuum growth technique has been employed for the first time to grow thin films of ZnSnP$\sb2$. Near stoichiometric thin films of polycrystalline ZnSnP$\sb2$ have been grown on GaAs and quartz substrates. A reasonable degree of reproducibility of the film composition from one run to the next was achieved by using a quadrupole mass analyzer probe in conjunction with a digital feedback controller to maintain constant Zn flux. The growth parameters for the system including the estimates for the Zn/Sn flux ratio at the substrate and the optimum substrate temperature have been obtained for the near stoichiometric film growth. The most uniform films showed less than $\pm$0.75% variation in the atomic composition for each of the three elements across a 1 cm$\sp2$ sample. The quality of layers grown on GaAs substrates was superior to those on quartz substrates. Different analytical techniques were used to characterize the grown films. The relations between film surface morphology and film composition were obtained from SEM and EDS analyses. The film morphology was most sensitive to the Zn content in the film. An absorption coefficient of greater than 10$\sp5$ cm$\sp{-1}$ was obtained without taking surface scattering into account. The energy gap value of 1.62 eV was observed from the optical transmission analysis. X-Ray diffraction analysis indicated that the grown films have chalcopyrite structure with lattice constant values in the range of 5.64-5.67 A. Silver and Indium were used to form electrical contacts to the grown films. Resistivity and Hall measurements were made in the temperature range of 300-625$\sp\circ$K. All the films examined were of p-type conductivity and the film resistivity was in the range of 0.1-10 $\Omega$-cm. The carrier concentrations in these p-type films were in the range of 10$\sp{16}$-10$\sp{18}$ cm$\sp{-3}$ and the room temperature Hall mobility values were in the range of 35-47 cm$\sp2$/V-sec. A small decrease in the bulk resistivity value was observed at 77$\sp\circ$K. Heterostructure diodes fabricated from the p-type ZnSnP$\sb2$ films grown on n-type GaAs substrates showed a small photoresponse demonstrating the feasibility of photovoltaic application of the grown material.

Pages

111

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