Swept away [quantum-well infrared photodetectors]

The ultra high-speed capability of quantum-well infrared photodetectors (QWIPs) is well known, thanks to their intrinsic short carrier lifetime (∼5 ps). This obviously makes QWIPs well suited for high-speed and high-frequency applications. In the past, for thermal infrared imaging where devices are optimized to have the highest possible detectivity, the absorption quantum efficiency has been low (<10%). For high-speed applications where lasers are usually used, the most important parameter is the absorption efficiency. We show that high absorption (∼100%) can be easily achieved by simply changing some of the device parameters. We also review the experimental demonstrations of the high-speed capability. At present, QWIPs hold the unique position of having high-speed/-frequency capability and high absorption for the thermal infrared region. There are no competitive alternatives.