Assessment of the ionized EL2 fraction in semi-insulating GaAs

Both optical and electrical methods were used to provide separate evaluations of the fraction Pi of EL2 defect donors which have lost an electron. The semi-insulating GaAs which permitted these assessments had a large enough fraction of the EL2 compensated (by CAs acceptors) to make this a sensitive test. Room-temperature Hall effect data, analyzed with an ambipolar correction, indicated that Pi ≂0.34 in material from a vertical-zone grown crystal, while near-infrared optical absorption could be modeled on a superposition of EL2 photoionization and photoneutralization to yield Pi ≂0.35 in the same crystal. The presence of compensating CAs acceptors was verified by local mode vibrational absorption.