DONOR STATES IN GAAS UNDER HYDROSTATIC-PRESSURE

Spectroscopic studies have been carried out for GaAs crystals under hydrostatic pressure, intended for the investigation of effective-mass donor levels associated with different conduction-band minima and the DX center. Our results reveal the existence of three donor states appearing in the band gap. These are labeled D-GAMMA, D*, and D(X). The donor state D-GAMMA, normally observed at atmospheric pressure, successively crosses two other donor states (D* and D(X)) as the hydrostatic pressure exceeds 28 kbar. D*, in turn, crosses D(X) at pressures of about 44 kbar. From their corresponding donor-accept pair luminescence, we know that D-GAMMA and D(X) have pressure dependences that track the GAMMA- and X-band minimum, and are believed to be effective-mass donor states associated with the GAMMA- and X-band edges, respectively. The third donor state D* has a pressure dependence that does not seem to agree with any known conduction-band minimum. However, it is in many respects similar to the DX center, although it has not, in studies of radiative emission, revealed evidence of a large lattice relaxation and photoquenching effects.