The growth of CdHgTe on GaAs and fabrication of high-quality photodiodes

Abstract

The use of metal organic vapor phase epitaxy (MOVPE) for the growth of device quality CdHgTe (MCT) on GaAs has been studied extensively. This is the first report of diode formation by mercury diffusion in the MOVPE grown material. It is also the first report of medium-wavelength infrared (MWIR) photodiodes made in the material. The effect of altering the cadmium to tellurium alkyl ratios on the growth of a CdTe buffer on (100) and (111)GaAs was investigated. For every alkyl ratio used, it was possible to grow (111) or (100)CdTe on (100)GaAs. (100)CdTe/(100)GaAs samples exhibited very sharp, well-defined photoluminescence spectra and x-ray rocking curve full width half-maximum (FWHM) peaks of <90 arc s were found for layers of 6–10 μm thick. Generally the (111)CdTe/(111)GaAs layers were dominated by twins, but the growth of untwinned (111)CdTe and MCT is reported. CdTe, high x MCT, and combinations of CdTe and HgTe layers were used as buffers for (100)MCT growth to reduce the hillock density. The combinations of CdTe and HgTe layers gave rise to the lowest hillock density (at best 30–100/cm2) over a large area (25×25 mm2). FWHMs of 80–90 arc s are routinely achieved for (100)MCT layers. Linear diode arrays have been fabricated with 77 K R0A values typically of 3×103 Ω cm2 for 7.5 μm cutoff. The detectivity of a 5.5 μm cutoff diode was 1.5×1011 cm Hz1/2 W−1 at 77 K, and 1.3×1010 cm Hz1/2 W−1 at 193 K. This is comparable to the performance obtained with the best traveling heater method devices.