Optical absorption in Zn_xHg_1-xTe thin films

Abstract

The optical transmittance and reflectance have been measured for thin films ( approximately 1 mu m) of ZnxHg1-xTe. Values for the energy gaps, estimated from the position of the absorption edge show that the system is a 'zero-gap' alloy similar to CdxHg1-xTe. A rigorous evaluation of the absorption coefficient has been made for compositions in the range 0<or=x<or=0.14. Calculations for direct transitions, assuming a zero-gap system, give results that are in good agreement with measured experimental values, for absorption coefficients less than 5000 cm-1. For values larger than 5000 cm-1 the agreement between theory and experiment is better if the effects of higher bands on the E-k relationship of the conduction band are also taken into account. An anomalous shift in the absorption curves after annealing in Ar is found and thought to be due to stress relief within the film.