Development and fabrication of two-color mid- and short-wavelength infrared simultaneous unipolar multispectral integrated technology focal-plane arrays

Abstract

We report the development and fabrication of two-color mid-wavelength infrared (MWIR) and short-wavelength infrared (SWIR) HgCdTe-based focalplane arrays (FPAs). The HgCdTe multilayers were deposited on bulk CdZnTe (ZnTe mole fraction ∼3%) using molecular beam epitaxy (MBE). Accurate control of layer composition and growth rate was achieved using in-situ spectroscopic ellipsometry (SE). Epilayers were evaluated using a variety of techniques to determine suitability for subsequent device processing. These techniques included Fourier transform infrared (FTIR) spectroscopy, Hall measurement, secondary ion mass spectroscopy (SIMS), defect-decoration etching, and Nomarski microscopy. The FTIR transmission measurements confirmed SE’s capability to provide excellent compositional control with run-to-run x-value variations of ∼0.002. Nomarski micrographs of the as-grown surfaces featured cross-hatch patterns resulting from the substrate/epilayer lattice mismatch as well as various surface defects (voids and “microvoids”), whose densities ranged from 800–8,000 cm⁻². A major source of these surface defects was substrate particulate contamination. Epilayers grown following efforts to reduce these particulates exhibited significantly lower densities of surface defects from 800–1,700 cm⁻². Dislocation densities, as revealed by a standard defect-decoration etch, were 2–20×10⁵ cm⁻², depending on substrate temperature during epitaxy. The FPAs (128×128) were fabricated from these epilayers. Preliminary performance results will be presented.