Properties of p -Type GaAs Prepared by Copper Diffusion

Purification of arsenic by hydrogen sublimation and gallium by vacuum annealing resulted in the preparation of high resistivity (∼106 ohm-cm), n-type GaAs crystals by the horizontal Bridgman technique. Conversion of this material to p-type was accomplished by the inward diffusion of copper from the crystal surface. Measurements of Hall mobility as a function of hole concentration in the range, 2×1016 cm−3 to 3×1017 cm−3, at room temperature showed a dependence which is consistent with theory. The analysis suggests a lattice mobility for holes of 450 cm2 V−1 sec−1 at 300°K. The mobility varied approximately as T−2.3 in the range 76°–300°K. At the low temperatures the number of ionized impurities ranged from 2×1015 cm−3. The energy levels associated with copper in GaAs are 0.023 ev and 0.15 ev above the valence band.