TEMPERATURE-DEPENDENCE OF THE FUNDAMENTAL ABSORPTION-EDGE OF MERCURY CADMIUM TELLURIDE

We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1-xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three-dimensional theory of direct-allowed excitons, we find precise values for the fundamental Γ8-Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury-rich Hg 1-xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=-0.303(1-x)+1.606x-0.132x(1-x)+[6.3(1-x) -3.25x -5.92x(1-x)]10-4T2/[11(1-x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band-gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far-infrared detection as well as optical-fiber communications performed at realistic values of the temperature) and gives accurate values for the temperature and composition dependence of the effective mass in the semiconducting range of alloys.