77 K FAR-INFRARED HOT-ELECTRON MULTI-QUANTUM-WELL DETECTORS

The responsivity to long wavelength (513 and 1253 mu m) far-infrared ( FIR) radiation and the root mean square noise voltage has been measure d for one bulk GaAs and two GaAs/AlGaAs multiquantum/well (MQW) hot-el ectron photodetectors as a function of temperature from 4.49 to 77 K. From these data the noise-equivalent power (NEP) was determined for ea ch device over the same temperature range. The MQW detectors were meas ured to have 77 K responsivities and NEPs that were one to two orders of magnitude better than those measured using the high purity bulk GaA s sample. To the best of our knowledge, these are the first measuremen ts which show that hot electron MQW detectors are able to outperform b ulk GaAs detectors at 77 K. Furthermore, the photoresponse of the MQW structures showed a much slower temperature dependent rolloff as compa red to the bulk device, which implies a potential for applications at temperatures above 77 K. Detection of nanosecond pulses of 496 mu m FI R radiation by one MQW detector and the bulk GaAs is additional eviden ce of hot-electron photoconductivity. (C) 1998 American Vacuum Society .