Hot electron photoconductivity in GaAs/(Ga,Al)As multiquantum-wells and bulk GaAs.

摘要

The far-infrared (FIR) photoconductive response (PR) as a function of temperature of one bulk GaAs and two GaAs/AlGaAs multiquantum-well (MQW) photoconductive detectors, comparably doped, has been compared at FIR wavelengths of 513 and 1253 ;The temperature dependence of the responsivity was measured at both wavelengths for all three photodetectors between 4.49 and 77 K and the noise equivalent power (NEP) of each device vs. temperature was determined. The results of these experiments show that the responsivity and noise-adjusted NEP of the MQW's are better than that of bulk GaAs at temperatures ;The noise characteristics of each device were determined by measuring their noise spectra from 20 Hz to 1 MHz at the same temperatures and bias conditions that the responsivity experiments were conducted. The noise spectra showed that the MQWs exhibited substantial 1/f noise, which is characteristic of poor ohmic contacts. This led to the development of a noise-adjusted NEP value for the MQWs which allowed a fairer comparison of NEP values to those of bulk GaAs. Beyond 1 MHz, the noise voltage of the bulk GaAs and the MQW samples was equivalent.;The PR to 496 ;Because the MQWs have a better responsivity and NEP than bulk GaAs by one to two orders of magnitude at 77 K, they are useful as liquid-nitrogen-cooled detectors of radiation from high-power (;This dissertation includes descriptions of the CW and pulsed laser systems, all of the photodetectors used in the experiment, the FIR power measurement system, experimental techniques and relevant theoretical concepts. The potential of MQW detectors and suggestions for future work are discussed in the final sections.