Optical absorption inHg1−xCdxSealloys

Abstract

Infrared transmission measurements between 1 and 25 \ensuremath{\mu}m are reported for ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Se}$ alloys with $0.15<x<0.68$ and electron concentrations between 1 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ and 9 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ at temperatures between 5 and 300 K. The data have been analyzed to obtain the refractive index and the intrinsic-absorption-coefficient spectrum for each sample and sample temperature. From fits of these data using an optical-absorption theory based on the Kane three-band model, accurate values for the fundamental energy-gap and conduction-band parameters were obtained. Empirical relationships are reported for the dependences of the refractive index, fundamental energy gap, and energy-band parameters on alloy composition and temperature. For temperatures between 5 and 300 K the refractive index decreases with increasing $x$ values and at 5 K has values of 3.92 and 2.68 for $x$ values of 0.153 and 0.684, respectively. For the same temperature and range of alloy compositions, the energy gap increases from 0.031 to 1.029 eV. The dependence of the energy gap on alloy composition bows slightly below a linear interpolation between the energy gaps of HgSe and CdSe. Like other II-VI and IV-VI ternary alloy systems, low-$x$ ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Se}$ alloys exhibit large, positive, energy-gap temperature coefficients.