A study was made of the Poole-Frenkel effect in this material. The results showed that ignoring the effect in deep-level transient spectroscopic investigations led to a significant scatter in the activation energies which were reported for deep defects. The Ga-doped films which were used here were grown on (100)GaAs by means of molecular beam epitaxy. Deep-level transient spectroscopic results revealed the presence of 2 prominent electron traps at 0.27eV and at 0.40 to 0.48eV. The latter trap exhibited a strong Poole-Frenkel effect; thus indicating a donor-like character. Thermal emission from the lower-energy trap was independent of the electric field. By taking account of the Poole-Frenkel effect, it was possible to explain the carrier-concentration dependence of the activation energy of the higher-energy trap. The capture process for the lower-energy trap was thermally activated, with a thermal-energy barrier of 0.096eV. The existence of a thermal barrier to carrier capture led to a persistent photoconductivity below 90K. In order to describe the properties of Ga-related traps, a consistent defect model was proposed which involved complexes of Ga atoms with Zn vacancies in next-nearest neighbor positions (GaZn-VZn). The model attributed the higher-energy level to a donor-like state, and the lower-energy level to an acceptor-like state of a GaZn-VZn defect complex.

B.Hu, G.Karczewski, H.Luo, N.Samarth, J.K.Furdyna: Physical Review B, 1993, 47[15], 9641-9