Germanium-doped GaAs crystals were grown on GaAs seeds from Ga solution. The properties of the Ge-doped GaAs layers were examined by Hall effect measurements from 20° to 400°K and by photoluminescence measurements between 12° and 300°K. It was found that Ge-doped GaAs is always p-type when grown at 900°–875°C from Ga solution containing 56 at.% or less Ge. The temperature dependence of the Hall coefficient and the photoluminescence experiment indicated an acceptor energy level of 0.035 and 0.038 eV respectively. It was also found that at least 85% of the Ge was present as an acceptor in the GaAs crystals when the growth solution contained two atom percent or less Ge.
GaAs p-n junctions were grown by liquid-phase epitaxy using Ge as the acceptor and Sn as the donor. Abrupt junctions with well-controlled carrier concentrations in both the n and the p layers were produced. High-quality varactors and double-drift GaAs IMPATT diodes were fabricated. cw output power of 3.0 W with 15.8% efficiency at 8.9 GHz and pulse output power of 4.1 W with 20.7% efficiency at 10.56 GHz were observed.
Gallium arsenide crystals doped with germanium were grown from gallium solutions at 900°–875°C. The Ge concentration in the liquid was varied from 0.004 to 56 at.%, and the Ge concentration in the GaAs crystals determined using radiotracer and other techniques. The Ge concentration in the solid varied linearly with increasing Ge concentration in the liquid up to 5 at.% and kGe = (Ges)/(Gel)=0.0083±0.001. Above 5-at.% Ge in the growth solution, kGe increased. At low doping levels Ge acts predominantly as a simple acceptor substituting on arsenic sites. At high doping levels, in the extrinsic range, the Ge concentration in the solid is considerably greater than the free carrier concentration. The form in which the excess Ge exists is not known.
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