Energy band gap, intrinsic carrier concentration, and Fermi level of CdTe bulk crystal between 304 and 1067 K

Optical transmission measurements were performed on CdTe bulk single crystals. It was found that when sliced and polished CdTe wafers were used, a white film started to develop on the sample surface and the wafer became opaque when it was heated above 530 K. Therefore, a bulk crystal of CdTe was first grown in the window area by physical vapor transport. The optical transmission was then measured between 304 and 1067 K and from which the energy band gap was derived. The band gaps of CdTe can fit well as a function of temperature by the Varshni expression. Using the band gap data, the high temperature electron-hole equilibrium was numerically calculated by assuming Kane's conduction band structure and a light-hole and a heavy-hole parabolic valence bands. The calculated intrinsic carrier concentrations agree well with the experimental data previously reported. The calculated intrinsic Fermi levels between 200 and 1200 K were also presented.