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 results were analyzed in detail by using the grand partition function formalism assuming multiple acceptor levels with both single and double occupancy. It is shown that p-type conduction is originated from the presence of a residual shallow acceptor and several deep acceptor levels. For the samples having relatively high concentration of shallow accepters, deep aeceptor states with the ionization energies of about 90 and 200 meV are determined, which are likely associated with the presence of double acceptor centers. In the high purity samples, however, deeper aceeptor levels are required to account for the data.