Properties of HgCdTe layers grown by isothermal vapour phase epitaxy at high pressure

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Abstract
A modified approach for epitaxial growth of HgCdTe (MCT) by isothermal vapour phase epitaxy (ISOVPE) under high hydrogen pressure is reported. The growth and anneal are carried out in a re-usable and demountable internally heated high-pressure furnace. The technique offers a low-cost, easily implemented alternative to other ISOVPE growth techniques which include sealed quartz ampoule and open-tube growth. By controlling the hydrogen pressure in the 600-1200 psi range (4.1-8.2 MPa) during a Hg anneal in the 450-550 degrees C temperature range, the gradient in the MCT composition can be controlled and tailored. Using this approach the authors report MCT epilayer growth on (111)B CdTe and CdZnTe with thickness uniformity to within 1.5% over a 6 cm2 area. Compositional uniformity as measured by 300 K FTIR transmittance indicates a cut-off wavelength of 6.3 mu m to within 0.1 mu m measured over the same area. Undoped n-type epilayer mobilities in the range of (2-7)*104 V-1 s-1, carrier concentrations of (2-8)*1014 cm-3 and excess carrier lifetimes as high as 1 mu s at 80 K are reported. In addition, photoconductive detectors fabricated from ISOVPE epilayer material have yielded 80 K responsivity >8*104VW-1 and a D* value of 1.5*1010 cm Hz0.5 W-1 measured over the 8-11 mu m spectral band.