Effect of Temperature Cycling on Conduction Mechanisms in CdTe Thin Films

Abstract

CdTe thin films of 500 A thickness prepared by thermal evaporation technique were analyzed for leakage current and conduction mechanisms. Metal–insulator–metal (MIM) capacitors were fabricated using these films as a dielectric. These films have many possible applications, such as passivation for infrared diodes that operate at low temperatures (80 K). Direct-current (DC) current–voltage (I–V) and capacitance–voltage (C–V) measurements were performed on these films. Furthermore, the films were subjected to thermal cycling from 300 K to 80 K and back to 300 K. Typical minimum leakage currents near zero bias at room temperature varied between 0.9 nA and 0.1 μA, while low-temperature leakage currents were in the range of 9.5 pA to 0.5 nA, corresponding to resistivity values on the order of 108 Ω-cm and 1010 Ω-cm, respectively. Well-known conduction mechanisms from the literature were utilized for fitting of measured I–V data. Our analysis indicates that the conduction mechanism in general is Ohmic for low fields 6 × 104 V cm−1 is modified Poole–Frenkel (MPF) and Fowler–Nordheim (FN) tunneling at room temperature. At 80 K, Schottky-type conduction dominates. A significant observation is that the film did not show any appreciable degradation in leakage current characteristics due to the thermal cycling.