Compositional dependence of electrical conduction in solution grown Zn_1−xCr_xSe thin films: a correlation

Abstract

Zinc selenide (ZnSe) has a typical band gap of 2.7 eV suitable for window application and can easily be synthesized using a liquid phase chemical bath deposition. An attempt is made to tune its band gap and other characteristics to cope with a maxima of the solar spectrum by deliberate addition of Cr³⁺. ZnSe and Zn_1−xCr_xSe (0 ≤ x ≤ 0.35) thin films were obtained under the controlled deposition conditions (temperature = 70 °C, time = 210 min, pH = 10, etc). The compositional analysis showed Zn²⁺ replacement by Cr³⁺. The X-ray photoelectron spectroscopy revealed chemical states of the constituents Zn, Cr and Se as 2⁺, 3⁺ and 2⁻ respectively. The electrical conductivity and thermo-power measurements in the 300–550 K temperature range showed semiconducting nature of the material and that the electrical conduction is of the n-type. The electrical conductivity is found to be increased continuously up to x = 0.05 and then decreased for further increase in x. The Hall-probe measurements also confirmed n-type conduction. The average Hall coefficient for pure ZnSe is −1.03 × 10⁷ cm³/C whereas, it is −4.55 × 10⁶ cm³/C for a sample with x = 0.35.