Urbach tail and nonuniformity probe of HgCdTe thin films and quantum well heterostructures grown by molecular beam epitaxy

Temperature-driven photoconductivity spectra are studied in HgCdTe thin films and quantum well (QW) heterostructures grown by molecular beam epitaxy (MBE). It is shown that the absorption edge steepness in narrow gap HgCdTe epilayers approaches the fundamental limit. The corresponding Urbach energy is 1.5 to 4 meV at 4.2 to 77 K, which is an order of magnitude lower than values reported previously, indicating a significant progress in the quality of structures grown by MBE. Auger-suppressed multi-QW heterostructures that can be used for development of long-wavelength lasers/detectors are shown to have the comparable steepness of the absorption edge. The corresponding “Urbach” energy is much less than the threshold energy of the Auger recombination, which means that furthering the operating wavelengths beyond 20 μm is feasible for optoelectronic devices based on HgCdTe structures

Non-Radiative Transitions of Holes on Mercury Vacancies in Narrow-Gap HgCdTe

Mercury vacancies, acting as double acceptors, are the dominant point defects in ternary HgCdTe alloys. Though HgCdTe is one of the leading materials in infrared optoelectronics, the energy spectra of the vacancies are still a matter of some debate. This work investigated the rates at which holes are captured to a singly ionized mercury vacancy via acoustic phonon emission in narrow-gap Hg1−xCdxTe with technologically relevant x~0.22. Combined with the calculated rates of intracenter transitions, the data allow one to predict the most pronounced optical transitions in the emission spectrum of a double-charged acceptor. The results are sustained by the photoluminescence spectroscopy in the terahertz domain, allowing one to identify the emission band that is related to neutral vacancies

Non-Radiative Transitions of Holes on Mercury Vacancies in Narrow-Gap HgCdTe

Mercury vacancies, acting as double acceptors, are the dominant point defects in ternary HgCdTe alloys. Though HgCdTe is one of the leading materials in infrared optoelectronics, the energy spectra of the vacancies are still a matter of some debate. This work investigated the rates at which holes are captured to a singly ionized mercury vacancy via acoustic phonon emission in narrow-gap Hg1−xCdxTe with technologically relevant x~0.22. Combined with the calculated rates of intracenter transitions, the data allow one to predict the most pronounced optical transitions in the emission spectrum of a double-charged acceptor. The results are sustained by the photoluminescence spectroscopy in the terahertz domain, allowing one to identify the emission band that is related to neutral vacancies

Stimulated Emission up to 2.75 µm from HgCdTe/CdHgTe QW Structure at Room Temperature

Heterostructures with thin Hg(Cd)Te/CdHgTe quantum wells (QWs) are attractive for the development of mid-infrared interband lasers. Of particular interest are room-temperature operating emitters for the short-wavelength infrared range (SWIR, typically defined as 1.7–3 μm). In this work, we report on the observation of stimulated emission (SE) in the 2.65–2.75 µm wavelength range at room temperature in an optically pumped HgCdTe QW laser heterostructure. We study a series of three samples with lengths ranging from 2.5 to 7 mm and discuss the effects related to the non-uniformity of the excitation beam profile. SE threshold intensity and the magnitude of pump-induced carrier heating are found to be effectively dependent on the chip size, which should be accounted for in possible designs of HgCdTe-based optical converters. We also pay attention to the problem of active medium engineering in order to push the SE wavelength towards the 3–5 µm atmospheric window and to lower the SE threshold