Persistent photoconductivity and photo-Hall studies were made of Sn-doped and Si-doped AlxGa1-xAs layers, where x was between 0.25 and 0.5. These results were correlated with previous photo-electron paramagnetic resonance results which were obtained using the same samples. This revealed the importance of hydrogenic effective-mass states that were derived from secondary conduction band minima in highly doped (above 1018/cm3) samples. Fermi-level pinning, by the resonant T2(X) level in Sn-doped samples of direct-gap material after low-temperature photo-excitation, was directly demonstrated by its detection via electron paramagnetic resonance. This explained the difference in spin and carrier concentrations which were observed, as well as the differing kinetics of relaxation to the initial state.

A.E.Belyaev, J.S.Ryabchenko, M.K.Sheinkman, H.J.Von Bardeleben: Semiconductor Science and Technology, 1996, 11[1], 68-73