P-Type Gallium Arsenide Epitaxial Growth

At the beginning of this program, the rapid development of double-drift GaAs IMPATT diodes at X-band was being retarded by limited knowledge of the optimum growth conditions and the basic physical properties of p-type GaAs. Although p-type material with doping levels suitable for X-band double-drift devices was grown before this program began, profile control was sometimes erratic and wafer yield was poor. There was also a serious need for further data on hole velocities and ionization coefficients at the temperatures and electric fields existing in double-drift devices. In the first task of this program, we explored three p-type doping techniques, one involving zinc alkyl, and two involving zinc iodide formed as needed by chemical reaction. The zinc alkyl process was found to be chiefly useful for p++ contacts; the two zinc iodide processes gave useful p-doping at levels suitable for devices form X- to Ka-band. In the second task of this program, we measured hole velocities as a function of electric field and temperature which averaged about 70 percent of those reported previously. We also determined ionization coefficients at very high fields, typical of high power Ka-band devices. In the third task, we grew X-band and Ka-band p-type low-high-low Read wafers with good reproducibility.