Investigation of multicolor quantum well and quantum dot infrared photodetectors

Infrared detectors have a wide range of applications, such as night vision, optical communication, and surveillance. Over the past few decades, development of new materials and structures has been driven by the requirements of more efficient, faster, and cheaper infrared detectors and maturity of material growth and fabrication technologies. There are mainly two types of infrared detectors, thermal detectors and photon detectors. In a thermal detector, the incident radiation is absorbed due to certain physical property and sequentially generates an electrical output. On the other hand, for a photon detector, radiation is absorbed within the material by interaction with charge carriers. The output electrical signal results from the changed electronic energy distribution. As a result, photon detectors show higher sensitivity and faster response time. In addition, multispectrum detection can be realized in quantum well infrared photodetectors (QWIPs) and quantum dot infrared photodetectors (QDIPs). At present, research on QWIP and QDIP is focusing on multicolor detection and room-temperature operation.;Multicolor detection is desirable for various applications, for instance, laser designator and firefighting. The objective of this work is to fabricate and characterize QWIPs and QDIPs with multicolor detection in the infrared range. The quality of the grown materials was evaluated by structural and optical characterization techniques. The photodetectors were fabricated using processing techniques including photolithography, chemical wet etching, metal deposition, lift-off and rapid thermal annealing. We established two ways to successfully realize multicolor detection: use interband transition and intersubband transition from one structure and stack two or more structures with different detection wavelengths. Multicolor detection was achieved from both QWIP and QDIP based interband transition and intersubband transition, and interband transition was more often observed from QDIPs compared with QWIPs. Photoresponse ranging from visible and near infrared (NIR) to long wavelength infrared (LWIR) was observed from both QWIP and QDIP. Room temperature operation at the visible and near infrared wavelength range was observed from QDIPs with high detectivity. Also, multicolor broadband detection was achieved from QDIP. Future work on QDIPs is discussed in the conclusion.