Optical and electrical characterization of vacuum deposited n-CdS/n-ZnS bilayers

A crucial comprehension of homopolar n-CdS/n-ZnS heterojunction is a key to design a solar device. Present study focuses on vacuum evaporated antireflective homopolar heterojunction with better spectral response as compared to single layer CdS. ZnS in combination with CdS facilitates minimized interface recombination losses and helps to attain large band bending by limiting conduction band spikes. With different thickness combinations of heterostructure, deviation in material properties such as lattice constant, band gap, has been observed. This further causes strain, defects, interface states, surface recombination centers and inter-diffusion leading to associated electro-optical changes. Thickness combination dependency of I-V properties of n-CdS/n-ZnS stack were numerically investigated using a new simulation software (wxAMPS) and examined with the experimental; where junction parameters were extracted using thermionic, Cheung's, and Norde models. Complexities faced in few thickness combinations which could hinder the ideal window character is also identified. The thickness combination with the lowest series resistance is presently referred to possess minimal resistive loss and high optical throughput.