Unintentionally doped GaAs crystals grown by the horizontal Bridgman method were annealed at temperatures in the range from 700 to 910thinsp;deg;C under As overpressure. Thenhyphen;type crystals subjected to heat treatment under As overpressure lower than the growing pressure revealed a conductivityhyphen;type conversion toptype. The electrical conductivity, Hall coefficient, and photoionization cross sections were measured on thephyphen;type samples, and the resulting analysis indicates that the conversion center is a double acceptor, most probably associated with CuGadefect. The activation energies attributable to the singly and doubly ionized states of the acceptor were found to be sim;150 and sim;380 meV at 0 K, respectively. The doubly ionized acceptor states turned out to provide strong spacehyphen;charge scattering, which plays a crucial role in determining the hole behavior in the present material at high temperatures.
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