Molecular beam epitaxial growth of HgCdTe midwave infrared multispectral detectors

Abstract
Molecular beam epitaxy (MBE) has been utilized to fabricate high performance HgCdTe infrared detectors with sensitivity to midwave infrared radiation in adjacent spectral bands for two-color thermal imaging applications. Growth of a multilayer HgCdTe device structure by MBE enables the use of an n-p-n device architecture that facilitates pixel-level registration of images in two separate spectral bands. Device structures were grown on CdZnTe(211)(B) substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve detection of infrared radiation in adjacent spectral bands in the 3.5–4.5 μm wavelength range. As-grown device structures were characterized with x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. Mesa type devices were patterned using reactive ion etching and ohmic contacts were made to the two n-type layers for operation of the detectors in a sequential detection mode. The spectral response characteristics of the devices are highly uniform across a 64×64 element array, with standard deviation in cutoff wavelength less than 0.01 μm and external quantum efficiencies greater than 70% in both bands. Sharp detector cutoffs enable spectral crosstalk less than 1% to be obtained for spectral bands with as little as 0.6 μm separation. Junction reverse-breakdown voltages in excess of 500 mV and 80 K dynamic resistance-area products for each component diode in excess of 1×106 Ω cm2 at ±100 mV operating bias have been demonstrated.

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