Characterization of semiconductor surfaces by femtosecond optical rectification

Abstract

The recent observation of the optical rectification of femtosecond electromagnetic waves provides an alternative optical technique to characterize the depletion fields at semiconductor surfaces and interfaces. The experimental setup is briefly described. The semiconductor samples were selected from a variety of III-V, II-VI, and group-IV semiconductors that have bandgaps less than the incident photon energy (2 eV). The exposed semiconductor surfaces exhibit surface states that pin or bend the energy bands near the surface or semiconductor-air interface, forming a charge-depletion region and a built-in surface electric field. Rectified fields from InP, GaAs, GaSb, InSb, CdTe, CdSe, and Ge samples were observed. Parameters that control the rectified field are the transient carrier mobility, the strength of the surface field, and the width of the depletion region. The strength and polarity of the surface fields were investigated by using several n- and p-type GaAs samples with doping concentrations from 1015/cm3 to 1019/cm3. The schematic illustration of an outward rectified field from a p-type GaAs sample is shown, and the measured results are given. The effect of an externally controlled bias on the rectified field has been verified by using Au/GaAs Schottky diodes, and the results are reported.