Electrical behavior of a static hole inversion layer at the i-AlAs/n-GaAs heterojunction

The photocapacitance-voltage and current-voltage characteristics of p+-GaAs/i-AlAs/n-GaAs heterojunction enhancement mode capacitors have been studied in the temperature range from 9.5 to 273 K. Under steady-state illumination, the emission mechanisms for a photopopulated hole inversion layer are found to be thermionic field emission at high temperatures and tunneling at low temperatures. Estimates are made of the minority-carrier recombination lifetime, valence-band discontinuity, and the tunneling effective mass for holes in the AlAs barrier layer. The decay of inversion hole concentration after terminating the photoinjection process is measured with a capacitance transient technique, which is sensitive to current levels below 1 pA. The dominant decay mechanisms at this current level are found to be injection to the substrate at low-inversion bias voltages and emission over the AlAs barrier via the Frenkel–Poole mechanism at high-inversion bias voltages.