Novel infrared devices based on semiconductor quantum structures

This presentation discusses two examples of devices under investigation in our group. The ultrahigh speed and frequency capability of quantum well infrared photodetectors; (QWIPs) is well known, thanks to the short intrinsic carrier lifetime (similar to5 ps). For high-speed applications where lasers are usually used, the most important parameter is the absorption efficiency. We show that high absorption (similar to100%) can be easily achieved by simply changing some of the device parameters. At present time, QWIPs hold the unique position of having high speed/frequency capability and high absorption for the thermal infrared region. There are no competitive alternatives. In connection with high-speed applications, we also discuss two-photon intersubband transition in quantum wells. For some special applications, intrinsic nonlinear QWIP properties are useful, such as in autocorrelation of short pulses by two-photon absorption. The other device discussed here is an integrated 1.5 to 1-mum up-converter based on InP, GaAs, and related compounds. The device consists of a serially connected 1.5-mum InGaAs PIN photodiode and 1-mum light-emitting diode. The operation of the device relies on (1) detecting a 1.5-mum signal by the photodiode and (2) driving the light-emitting diode by the resulting photocurrent, thus achieving up-conversion.