Characterization of photorefractive GaAlAs multiple quantum well structures by ac photoelectromotive force and modulated photocarrier grating techniques

Abstract

Simultaneous utilization of ac photoelectromotive (photo-EMF) and modulated photocarrier grating (MPG) techniques for characterization of bipolar transport in semi-insulating photorefractive GaAlAs multiple quantum well structure is reported. From the ac photo-EMF experiment the electrons were determined as the dominant photocarriers for interband optical excitation at λ=633 nm. From the self-consistent data obtained from photo-EMF and MPG experiments the diffusion length of the photoelectrons was evaluated as LD≃1.4±0.2 μm, and that of the photoholes (minority carriers)—as LDm≃0.6±0.1 μm. In the MPG configuration, the contrast of the illuminating interference pattern was controlled by electro-optic modulation of the signal beam polarization, which allowed us to measure dielectric relaxation time of the photoconductor as well. As evaluated by both techniques it proved to be about τdi≃0.05 μs for the average light intensity I0≃0.3 mW/mm2. The proposed combination of the characterization techniques seems to be especially promising for amorphous a–Si and polymer films.