Intrinsic carriers play a dominant role especially in the long wavelength (8-12 μm cut-off) HgCdTe material near ambient temperatures due to high thermal generation of carriers. This results in low minority carrier lifetimes caused by Auger recombination processes. Consequently, this low lifetime at high temperatures results in high dark currents and subsequently high noise. Cooling is one means of reducing this type of detector noise. However, the challenge is to design photon detectors to achieve background limited performance (BLIP) at the highest possible operating temperature; with the greatest desire being close to ambient temperature operation. We have demonstrated a unique planar device architecture using a novel approach in obtaining low arsenic doping concentrations in HgCdTe. Results indicate Auger suppression in P+/π/N+ devices at 300K and have obtained saturation current densities of the order of 3 milli Amps-cm2 on these devices.
We examine the potential of (211) HgTe/CdTe superlattices for applications involving the detection of very long wavelength infrared radiation (cut-off wavelengths longer than 15μm at 40K). The superlattice electronic band structures and radiative and Auger recombination rates were theoretically modeled. The layer widths were optimized to suppress Auger recombination. Several of the theoretically designed superlattices were grown to 200 periods on (211)CdTe/Si substrates and characterized. Both the layer widths and crystal quality were determined by means of x-ray diffraction measurements. The temperature dependent absorption coefficient was measured to determine the cut-off wavelengths. Theory and experiment are in close agreement for energies above 60meV. Reliable experimental data could not be extracted below 60 meV, however the computed H1-E1 energies are useful assessments of the actual cut-offs. We also present transmission electron microscopy images and secondary ion mass spectroscopy data of the grown superlattices. Our results demonstrate the feasibility of using superlattices in very long wavelength infrared detector structures.
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