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Mesa structures were etched in HgCdTe using different Br 2 /HBr/Ethylene glycol (EG) formulations. Etch rate and degree of anisotropy (A) were studied in detail for all of the combinations. Addition of EG to the conventional etchant gave A Ͼ 0.5, with controllable etch rates. Optimum etchant composition was determined to be 2% Br 2 in a 3:1 mixture of EG:HBr. This composition resulted in a good anisotropy factor of ϳ0.6 and a reasonably optimum etch rate of ϳ2.5 µm/min, with rms surface roughness of ϳ2 nm. Kinetics of the etching reaction have also been studied for the optimum etchant concentration and an etching mechanism has been proposed.

Bromine-and iodine-based solutions were compared for surface preparation of HgCdTe epilayers. The iodine (I)-potassium iodide (KI)-based non-aqueous solution for surface preparation of mercury cadmium telluride (HgCdTe) epilayers is less corrosive, less toxic and technologically more suitable compared to the widely used bromine-based etchants. It provides improved surface morphology and a lower amount of oxides. A comparative study of the oxide content and elemental tellurium residue on the polished surface was made by x-ray photoelectron spectrometry measurements. Least elemental Te content was observed on the HgCdTe surface polished with I-KI solution as compared to bromine-based etchants. It may result in reduced trap density at the surface of HgCdTe. The possibility of potassium diffusion due to I-KI polishing at the HgCdTe surface, as well as at the cadmium zinc telluride (CdZnTe)-HgCdTe interface, has been ruled out using secondary ion mass spectrometry. Performance of photodiodes fabricated on the polished epilayers (Hg 0.7 Cd 0.3 Te) was assessed and the zero bias dynamic resistance area product (R 0 A) was measured as >5 9 10 4 X cm 2 under stray illumination.

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The design of present generation uncooled Hg1−xCdxTe infrared photon detectors relies on complex heterostructures with a basic unit cell of type ṉ+/π/p̱+. We present an analysis of double barrier ṉ+/π/p̱+ mid wave infrared (x=0.3) HgCdTe detector for near room temperature operation using numerical computations. The present work proposes an accurate and generalized methodology in terms of the device design, material properties, and operation temperature to study the effects of position dependence of carrier concentration, electrostatic potential, and generation-recombination (g-r) rates on detector performance. Position dependent profiles of electrostatic potential, carrier concentration, and g-r rates were simulated numerically. Performance of detector was studied as function of doping concentration of absorber and contact layers, width of both layers and minority carrier lifetime. Responsivity ∼0.38 A W−1, noise current ∼6×10−14 A/Hz1/2 and D∗ ∼3.1×1010cm Hz1/2 W−1 at 0.1 V reverse bias have been calculated using optimized values of doping concentration, absorber width and carrier lifetime. The suitability of the method has been illustrated by demonstrating the feasibility of achieving the optimum device performance by carefully selecting the device design and other parameters.

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Transfer length method (TLM) structures were fabricated to characterize the Ti-HgCdTe contacts. Low-temperature measurement of contact resistance was found to be affected by the background-generated carriers in long wavelength infrared HgCdTe material. Measurements carried out by keeping the TLM structures behind a cold shield showed low contact resistance indicative of the formation of a good "Ohmic" contact. Low specific contact resistance of the order of 10 Ϫ4 Ω-cm 2 makes this contact scheme suitable for the fabrication of photoconductive as well as photovoltaic HgCdTe detectors. Annealing the contacts in air at 60°C for 15 days yielded the specific contact resistance values of the same order of magnitude at room temperature; however, low-temperature measurements show a minor change in the specific contact resistance. The current-voltage measurements show that current transport is dominated by the thermionic field emission mechanism.

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