The Hall mobility and Hall electronic concentration were measured, as a function of temperature, in 3 low-compensation n-type epilayers of similar thickness which were grown by chemical beam epitaxy. The Hall mobility of the samples was found to be exceptionally high at 77K, but was significantly depressed at 300C. At temperatures which were above the freeze-out region, strong Hall electronic excitation was consistently observed between 35 and 300K. These features were in excellent agreement with a model which accounted for a broad band of localized deep-donor centers, or complexes of unknown origin, which was centered at 0.16eV below the conduction band. In addition, all of the samples exhibited an anomalous metal-like behavior at the lowest temperatures, instead of the expected strong localization regime. A broad luminescent band with a line-width of about 0.011eV, which was linked to the presence of the band of deep donors, was observed below the acceptor bound-exciton transition. Time-resolved photoluminescence and photoluminescence excitation measurements supported the suggestion of a bound-exciton nature for the luminescent band.

R.Benzaquen, M.Benzaquen, S.Charbonneau, P.J.Poole, T.S.Rao, C.Lacelle, A.P.Roth, R.Leonelli: Physical Review B, 1994, 50[23], 16964-72