Influence of Temperature and Illumination on the Electrical Characteristics of Nanocrystalline $Cu_2S$ Based Heterojunctions for Photodetector Application

In this work, heterojunctions of $Cu_2S//p-Si$ were prepared by high vacuum thermal evaporation technique and examined as a photodetector structure. The dark current-voltage (I-V) characteristics of the heterojunctions measured at different temperatures ranging from 303 to 373 K were investigated. The predominant conduction mechanisms, series resistance, ideality factor and potential barrier height were determined. The downward curvature at sufficiently large voltages in the I-V characteristics is caused by the effect of series resistance $R_{s}$. The ideality factor obtained from I-V characteristics is larger than unity which can be attributed to the presence of a thin interfacial insulator layer between the metal and semiconductor. The photocurrent properties of the device under reverse bias using various illuminations were also explored for checking the validity of photodetector application of the studied device. The responsivity of light for the device under reverse bias confirms that the $Cu_2S//p-Si$ heterojunctions are valid for photodetector application. Moreover, these results suggest that the fabricated diode can be used for optical sensor applications. The capacitance-voltage characteristics of diode were also investigated at high frequency of 1 MHz