Electrical and Computer Engineering ETDs

Publication Date



MIS capacitors were fabricated on n-type GaAs 0.5 p 0.5 using a thermally grown chromium-doped insulator and chromium gate electrode. The fabrication procedures which lead to stable devices are described. The nature of the composite insulator, as well as that of a disordered layer of GaAs 0.5 P 0.5 underneath the insulator are discussed and related to observed electrical characteristics.

Flatband voltages for the capacitors subsequent to device fabrication ranged from -2.5 to -5 volts, corresponding to surface charge densities of 3.1 x 10 11 cm-2 to 4.3 x 10 11 cm-2. Fast interface state densities at flatband varied from 2.5 x 10 11 to 10 12 states/cm2 -eV. High-frequency c-v data for the MIS deviced are presented. The lack of inversion layer formation at large negative gate bias is attributed to the very low minority carrier generation rate in the wide bandgap GaAsP semiconductor.

The deviced were exposed to both Co 60 gamma rays and high-energy electrons. Radiation-induced flatband voltage shifts were less than +2 volts up to a total absorbed radiation dose of 10 8 rads (GaAsP) for gamma irradiation and 10 6 rads (GaAsP) for electron irradiation. The polarity of shifts indicates a net decrease in the positive charge initially present in the dielectric. A qualitative model which relies on carrier injection and trapping in the GaAsP disordered region is proposed to explain the observed radiation-induced space buildup in the capacitors.

Radiation-induced increases in the fast interface-state density were generally less than 15 percent of the pre-irradiation values and were found to be independent of radiation type and dose, as well as the gate bias applied during irradiation. Thermal annealing experiments show that the radiation-induced chare can be completely annealed at a temperature of 150° C, independent of the gate bias applied during annealing.

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

W. W. Grannemann

Second Committee Member

R. A. Colclaser

Third Committee Member

H. D. Southward