Multicolor quantum dot and quantum ring intersublevel photodetectors for mid-infrared and terahertz detection.

Abstract

Terahertz (THz) detectors are used in a broad range of applications, including homeland security, biomedical imaging, and space science. A major limitation of the current THz detectors is their low operating temperature (<80K), which necessitates incorporation of large expensive cryogentic cooling systems. A cost and weight reduction is possible if these cryogenic cooling systems are replaced by thermo-electric coolers. Such a design change require THz detectors operating at elevated temperatures (>120K). Quantum dot intersublevel photodetectors (QDIPs) and quantum ring intersubband detectors (QRIDs) have potential to operate at high temperatures with desirable performance characteristics, due to the three-dimensional confinement in the detector active regions. This dissertation is devoted to developing THz QDIPs and QRIDs operating at elevated temperatures. An In_0.4Ga_0.6As/GaAs multi-quantum dot layer intersublevel detector with response peaks in the THz range has been demonstrated. At 150K, the response in the 15--5.4 THz range has a peak responsivity of 0.05A/W and specific detectivity D* of 2x10<super>7</super>Jones for an applied bias of -2V. An InAs/GaAs QRID has been demonstrated with 3 distinct response peaks at -6.5, 10, and 12.5THz. The THz response is observed up to T=120K. At 80K, the responsivity of the peaks vary from 0.07A/W to 0.02A/W. The investigation of the multicolor characteristics of these detectors has also been conducted. Multicolor detection plays an important role in high-resolution imaging tasks. To elucidate the multi-response peaks, the electron energy levels in the QDs and QRs have been calculated by an 8 band <bold>k&middot;p </bold> method and an effective mass method, respectively. Addtionally, a resonant tunnel double barrier structure as a means to select these multi-detection peaks has been developed and applied in a QDIP design.