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Uncooled MWIR and LWIR photodetectors in Poland

Piotrowski J., Pawluczyk J., Piotrowski A., Gawron W., Romanis M., Kłos K.

Opto-Electronics Review

2010

Vol. 18, No. 3

318-327

The history, status, and recent progress in the middle and long wavelength Hg1-xCdxTe infrared detectors operating at near room temperatures are reviewed. Thermal generation of charge carriers in narrow gap semiconductor is a major limitation or sensitivity. Cooling is a straightforward way to suppress thermal generation of charge carriers and reduce related noise. However, at the same time, cooling requirements make infrared systems bulky, heavy, and inconvenient in use. A number of concepts to improve performance of photodetectors operating at near room temperatures have been proposed and implemented. Recent considerations of the fundamental detector mechanisms suggest that near perfect detection can be achieved without the need for cryogenic cooling. This paper, to a large degree, is based on the research, development, and commercialization of uncooled HgCdTe detectors in Poland. The devices have been based on 3D-variable band gap and doping level structures that integrate optical, detection and electric functions in a monolithic chip. The device architecture is optimized for the best compromise between requirements of high quantum efficiency, efficient and fast collection of photogenerated charge carriers, minimized thermal generation, reduced parasitic impedances, wide linear range, wide acceptance angles and other device features. Recent refinements in the devices design and technology have lead to sensitivities close to the background radiation noise limit, extension of useful spectral range to > 16 µm wavelength and picosecond range response times. The devices have found numerous applications in various optoelectronic systems. Among them there are fast scan FTIR spectrometers developed under MEMFIS project.

MOCVD growth of Hg₁₋xCdxTe heterostructures for uncooled infrared photodetectors

Piotrowski A., Madejczyk P., Gawron W., Kłos K., Romanis M., Grudzień M., Piotrowski J., Rogalski A.

Opto-Electronics Review

2004

Vol. 12, No. 4

453-458

We report here recent progress at VIGO/WAT MOCVD Laboratory in the growth of Hg₁₋xCdxTe (HgCdTe) multilayer heterostructures on GaAs/CdTe and other composite substrates for uncooled infrared photodetectors. The optimum conditions for the growth of single layers and complex multilayer heterostructures have been established. One of the crucial stages of the technology was CdTe nucleation on GaAs substrate. Successful composite substrates were obtained with suitable substrate preparation, liner and susceptor treatment, proper control of background fluxes and appropriate nucleation conditions. The other critical stage is the interdiffused 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. The practical implications for the IMP process are the CdTe/HgTe growth times that become comparable with transition times between the phases, characteristic for the MOCVD machine. The growth during transition stages is characterized by the non-optimum flow velocities and partial pressures that may induce poor morphology, reduce growth rate and cause other problems. This became especially acute for doped layers when large Cd/Te ratio is required for efficient incorporation and full activation of dopants. This has been solved by careful selection of hydrogen carrier gas and metaloorganics fluxes with suitable switching on and off times. Arsenic and iodine has 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 vapors. As the result, we are able to grow multilayer fully doped (100) and (111) heterostructures for various infrared devices including photoconductors, photoelectromagnetic and photovoltaic detectors.