DEEP ACCEPTOR LEVELS IN MOLECULAR-BEAM EPITAXIAL HIGH-PURITY P-TYPE GAAS

Deep acceptor impurities in high-purity, unintentionally p-type doped GaAs epilayers grown by molecular beam epitaxy have been investigated by variable temperature Hall effect measurements. The experimental res ults were analyzed in detail by using the grand partition function for malism assuming multiple acceptor levels with both single and double o ccupancy. It is shown that p-type conduction is originated from the pr esence of a residual shallow acceptor and several deep acceptor levels . For the samples having relatively high concentration of shallow acce pters, deep aeceptor states with the ionization energies of about 90 a nd 200 meV are determined, which are likely associated with the presen ce of double acceptor centers. In the high purity samples, however, de eper aceeptor levels are required to account for the data.