SURFACE PHOTOVOLTAGE SPECTROSCOPY OF N-N(-N(+) ALGAAS() AND P)GAAS HETEROJUNCTIONS/

A comparative study of n-n(+) and p-ni semiconductor heterojunctions h as been done using the surface photovoltage spectroscopy (SPS) in the chopped light geometry. Heterojunctions n-Al0.4Ga0.6As/n(+) GaAs and p -Al0.37Ga0.67As/n(+) GaAs and substrate n(+) doped GaAs have been stud ied in the wavelength range 600-1000 nm. A sharp decrease in SPS at th e band-gap energies of AlGaAs and GaAs with a broad peak in the subban d-gap region of GaAs has been observed. The magnitude of surface photo voltage (SPV), for a constant photon flux for n-n(+) samples, is less by more than two orders of magnitude than that for p-n(+) samples in t he wavelength range 645-870 nm. Changes in the dipole moments due to t he redistribution of excess carriers in the space-charge regions are i n opposite directions of the n-n(+) heterojunctions giving less SPV, w hile for p-n+ heterojunction. the changes in the dipole moments are in the same direction giving more SPV in comparison to the n-n(+) sample s. (C) 1998 American Institute of Physics.