ELECTRICAL CHARACTERISTICS OF NANOSTRUCTURED POROUS SILICON

Abstract

The special properties of nanostructured porous silicon (PS), such as large surface area, negligible reflectance and facile surface modification provide new opportunities for their application in various optical and electronic devices. An ohmic contact on the PS layer is crucial for the development of light-emitting devices, photodetectors, solar cells, biosensors, etc. Investigation of the electrical characteristics of structures based on PS layers provides important information on rectifying junctions, built-in potential, barriers, type of junction and its capacitance. In this paper, electrical characteristics, specifically current-voltage (I-V) and capacitance-voltage (C-V), of the diode structures Al/PS/n-Si/Al are analyzed. PS layers were formed on n-type monocrystalline Si wafers by electrochemical etching in an HF solution at constant current densities. All films were deposited onto PS layers by thermal evaporation. Measurements of electrical characteristics were carried out at room temperature and held in the dark. It was found that the electrical characteristics of the prepared structures strongly depend on the conditions for the formation of the nanostructured PS and, as a consequence, on the porosity and thickness of the PS layer. In particular, an increase in the current through the diode structure was observed with a decrease in the etching current density. The capacitance decreased with increasing the time and current density of the etching. According to the experimental results, the rectification of I-V is found to be caused by the junction’s barriers Al/PS and PS/n-Si. A band model of a diode structure Ai/PS/nSi/Al is proposed in order to explain the observed characteristics, the barrier height and ideality factor were calculated. The reduction in the junction capacitance with increasing the bias voltage results is due to the expansion of the depletion layer.