Dark Currents of Unipolar Barrier Structures Based on Mercury Cadmium Telluride for Long-Wave IR Detectors

Two types of long-wave infrared nBn-structures based on mercury cadmium telluride grown by molecular beam epitaxy on GaAs (013) substrates have been fabricated. For each type of device, the side walls of the mesa structures were passivated with an Al₂O₃ insulating film or left without passivation. The CdTe content in the absorbing layers was 0.20 and 0.21, and in the barrier layers, it was 0.61 and 0.63. The dark currents of the manufactured devices were studied in a wide range of voltages and temperatures. The values of the surface leakage component are found under various conditions. It has been shown that the surface leakage current density decreases upon passivation with an Al₂O₃ film. It was found that in the fabricated nBn-structures at room temperature, the surface leakage component dominates at reverse biases, and at forward biases, the dark current is determined by the combined effect of the surface leakage component and the bulk current component. From the Arrhenius plots, the values of the activation energies of the surface leakage current component were found, which are in the range from 0.05 to 0.10 eV at small reverse biases. At small reverse biases, upon cooling the samples, the role of the bulk component of the dark current increases, which at 180 K is approximately 0.81 A/cm². In the temperature range 200–300 K, the values of the dark current density exceed the values calculated according to the empirical Rule07 model by a factor of 10-100, which indicates the possibility of creating the long-wave infrared barrier detectors by decreasing the values of the surface leakage component.