Electrical Properties of CdS/Cu(In,Ga)Se2 Interface

We present an experimental method to measure and extract the interface density of states and fixed charge at the CdS/Cu(In,Ga)Se₂ (CIGS) interface using the capacitance-voltage technique applied to a metal-insulator-semiconductor structure. The density of interface states is on the order of 10¹⁰ to 10¹³cm^-2 eV^-1. The effective fixed charge at the interface is (7.8 ± 0.3) × 10¹¹cm² and due to positive charges. These electrical properties make the CdS/CIGS interface well passivated and to some extent resemble the SiN_x/p-Si interface. We also measure the inversion strength (i.e., Fermi level at the interface) and capture cross-section of interface states from admittance spectroscopy. Inputting the above extracted parameters into the extended Shockley-Read-Hall recombination formulation by Eades and Swanson [J. Appl. Phys. 58, 4267 (1985)], we calculate the surface recombination velocity of mid-to-high 10³cm·s^-1, which agrees reasonably with temperature-intensity dependent recombination analysis.