In the last two decades several new concepts of photodetectors to improve their performance have been proposed. New strategies are especially addressed to the group of so called high-operating-temperature detectors where - apart from increasing of operating temperature - both the size and power consumption reduction is expected. In this paper a new strategy in the photo-detector design is presented - the barrier detectors: CnBn; CnBnN+, CpBn and unipolar barrier photodiodes. In spite of considering barrier detectors based on AIIIBV bulk compounds and type-II superlattices as having theoretically a better performance than those based on HgCdTe, the latter compound is also used to fabricate barrier detectors. Among many new applications of barrier detectors the detection of explosives can be extremely important due to an increased threat of terrorist attacks. This paper presents the status of the barrier detectors and compares the performance of mid-wave HgCdTe barrier detectors and unipolar barrier photodiodes.
The paper reports on the photoelectrical performance of the long wavelength infrared (LWIR) HgCdTe high operating temperature (HOT) detector. The detector structure was simulated with commercially available software APSYS by Crosslight Inc. taking into account SRH, Auger and tunnelling currents. A detailed analysis of the detector performance such as dark current, detectivity, time response as a function of device architecture and applied bias is performed, pointing out optimal working conditions.
In the paper recent progress at VIGO/MUT (Military University of Technology) MOCVD Laboratory in the growth of Hg1-xCdxTe (HgCdTe) multilayer heterostructures on GaAs/CdTe substrates is presented. The optimum conditions for the growth of single layers and complex multilayer heterostructures have been established. One of the crucial stages of HgCdTe epitaxy is CdTe nucleation on GaAs substrate. Successful composite substrates have been obtained with suitable substrate preparation, liner and susceptor treatment, proper control of background fluxes and appropriate nucleation conditions. The other critical stage is the interdi#27;used multilayer process (IMP). The growth of device-quality HgCdTe heterostructures requires complete homogenization of CdTe-HgTe pairs preserving at the same time suitable sharpness of composition and doping profiles. This requires for IMP pairs to be very thin and grown in a short time. Arsenic and iodine have been used for acceptor and donor doping. Suitable growth conditions and post growth anneal is essential for stable and reproducible doping. In situ anneal seems to be sufficient for iodine doping at any required level. In contrast, efficient As doping with near 100% activation requires ex situ anneal at near saturated mercury vapours. As a result we are able to grow multilayer fully doped (100) and (111) heterostructures for various infrared devices including photoconductors, photoelectromagnetic and photovoltaic detectors. The present generation of uncooled long wavelength infrared devices is based on multijunction photovoltaic devices. The technology steps in fabrication of devices are described. It is shown that near-BLIP performance is possible to achieve at ≈ 230 K with optical immersion. These devices are especially promising as 7.89.5 um detectors, indicating the potential for achieving detectivities above 109 cmHz1/2/W.