Admittance measurements of acceptor freezeout and impurity conduction in Be-doped GaAs

Abstract

Carrier freezeout and impurity conduction in lightly doped p-type GaAs have been studied in two groups of p - type GaAs undoped AlxGa1-xAs p+-type GaAs capacitors. For one group the substrate doping was NS 5×1014 cm-3; for the other NS 5×1015 cm-3. From the temperature dependence of the appearance of a Gray-Brown dip in the capacitance-voltage curves at fixed frequency and temperature, the separation of the Be acceptor from the valence band, EA, is 20 meV for both groups. The activation energy for ac transport in p - type GaAs, EI, is determined from admittance measurements at fixed bias and variable temperature and frequency. For the lighter-doped samples, EI=1723 meV, which is consistent with the value of EA. For the heavier-doped samples, EI6 meV; ac transport is either through a well-defined impurity band separated by 6 meV from the energy level of an isolated acceptor, or by activated hopping. © 1991 The American Physical Society.