Linear and nonlinear intensity dependent refractive index of Hg1−xCdxTe

Abstract

The index of refraction n is calculated as a function of frequency and mole fraction x for the ternary compound Hg1−xCdxTe in terms of known experimental parameters and compared with recent experimental results. The theoretical result for n is obtained from a quantum mechanical calculation of the dielectric constant of a compound semiconductor, which has been successfully applied to a number of III–V and II–VI binary, ternary, and quaternary compounds for which experimental data are available. The refractive index is calculated in terms of basic material parameters only, with no adjustable constants. These material parameters consist of band-gap energy, effective electron mass, and effective heavy hole mass at the band edge, the lattice constant, the spin-orbit splitting energy, and the carrier concentration for n-type of p-type materials. If these parameters are known as functions of mole fraction x and temperature, the refractive index is completely determined as a function of frequency below the fundamental absorption edge. The change in refractive index with increasing temperature depends mainly on the change in band-gap energy with temperature and is expected to be positive for x>0.529 and negative for x<0.529 for Hg1−xCdxTe . A negative change in the refractive index at the absorption edge proportional to I1/3, where I is the incident radiation intensity, is predicted on passing radiation through a crystal if the change in carrier concentration of the initially unoccupied conduction band is assumed proportional to I.