Two semi‐insulating liquid‐encapsulated Czochralski GaAs cyrstals, one Cr‐doped and the other undoped, were annealed at 750 °C for 15 min in flowing H2. Each sample converted to conductingptype in the near‐surface region, due to the formation of acceptors atEv+0.1 eV. We have studied this phenomenon by electrical, optical, and analytical profiling techniques, and have determined conclusively that the acceptors in our samples arenotrelated to Mn accumulation, a commonly accepted explanation. It is argued that the 0.1‐eV center may arise from several possible sources, each exhibiting a VGa‐like state at this energy.
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