Structural and electronic properties of evaporated thin films of cadmium telluride

An investigation is made into the structure and dc electrical properties of evaporated CdTe thin film sandwich structures with thickness d of up to 1 μm. X-ray diffraction studies show that the films are microcrystalline with typical grain size 74 nm and with a preferred orientation in the [111] direction. Capacitance measurements indicate that the films have a relative permittivity of approximately 9.6. Room temperature current density-voltage (J–U) characteristics show ohmic conduction below a threshold voltage Ut and a power-law dependence with exponent 5.7 to 6.1 at higher voltages. This behaviour is interpreted in terms of space-charge limited conductivity controlled by an exponential distribution of traps below the conduction band edge. Further evidence for this conduction process is provided by a linear dependence of Ut on d2 and of log J on log d with approximate slope − 15. Analysis of the results yields a room temperature electron concentration n0 ≈ (1.2 to 4.8) × 1011 m−3 and an exponential trap distribution of concentration N(E) = N0 exp (− E/kTt) at an energy E below the conduction band edge, where N0 ≈ (1.63 to 2.08) × 1043 J−1 m−3 and Tt ≈ 1402 to 1493 K.