Abstract

Optically induced femtosecond electromagnetic radiation from semiconductor surfaces provides a novel optical technique to characterize multilevel static electric fields within the optical-absorption length. In addition, from the analysis of the waveform of the radiated field, the orientation and strength of the piezoelectric field can be estimated with a noncontact approach. We have measured the strain-induced piezoelectric fields in several (100)- and (111)-oriented strained-layer superlattices, including type I superlattices (GaSb/AlSb and InGaAs/GaAlAs) and staggered type II superlattices (InGaSb/InAs). The results show that only (111)-oriented samples have the macroscopic piezoelectric fields. Strain-induced fields with equal amplitudes but opposite polarities between the (111) A-face and (111) B-face samples have been observed. We have compared the electromagnetic radiation from the strained-layer superlattices and thin films; extremely fast electromagnetic pulses from (111)-oriented superlattices have been observed. The quantum-well structure in the superlattices limits the pulse duration of the transient photocurrent; it is possible to generate electromagnetic radiation having a pulse duration comparable with the photocarrier transit time across the quantum well.

© 1990 Optical Society of America