QUANTUM WELL INFRARED PHOTOCONDUCTORS IN INFRARED DETECTORS TECHNOLOGY

Abstract

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared (IR) detectors are presented. In comparative studies both photon and thermal detectors are considered. More attention is paid to photon detectors and between them we can distinguish: HgCdTe photodiodes, InSb photodiodes, Schottky barrier photoemissive detectors, and doped silicon detectors. Special attention has been paid to competitive technologies in long wavelength IR (LWIR) and very LWIR (VLWIR) spectral ranges with emphasis on the material properties, device structure, and their impact on FPA performance. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation. From the discussion results, LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation(> 70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in the temperature range below 50 K due to problems involved in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though the QWIP is a photoconductor, several its properties such as high impedance, fast response time, long integration time, and low power consumption, well comply with requirements for large FPAs fabrication. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for VLWIR FPA applications in terms of the array size, uniformity, yield and cost of the systems. Both HgCdTe photodiodes and quantum well infrared photodetectors offer multicolor capability in the MWIR and LWIR range. Powerful possibilities of QWIP technology are connected with VLWIR FPA applications and with multicolor detection. QWIP FPAs combine the advantages of PtSi Schottky barrier arrays (high uniformity, high yield, radiation hardness, large arrays, lower cost) with the advantages of HgCdTe (high quantum efficiency and long wavelength response).