Identification of defect types in moderately Si-doped GaInNAsSb layer in p-GaAs/n- GaInNAsSb/n-GaAs solar cell structure using admittance spectroscopy

Abstract

Bias dependence of the admittance spectroscopy of GaInNAsSb based solar cell structure has been performed to identify and characterize the type of defects, for example interface and/or bulk type defects in a moderately Si doped GaInNAsSb (n-GaInNAsSb) layer in the structure. From the zero bias admittance spectrum, three peaks namely E1, E2, and E3 corresponding to the localized level at 0.03 eV, 0.07 eV, and 0.16 eV below the conduction band edge (EC) of n-GaInNAsSb material, respectively, were found. Constant position of E2 and E3 peak in the admittance spectra in response to the various applied DC reverse bias suggests that E2 and E3 are related to the bulk type defects being spatially homogeneous throughout the bulk of the n- GaInNAsSb film. However, bias dependence admittance of the E1 peak along with the capacitance - voltage (C-V) measurement as well as characteristic feature in the temperature dependent junction capacitance value strongly suggests that E1 peak might be originated due to the free carrier relaxation in the n- GaInNAsSb layer in lower temperature. Conduction mechanism in the freeze-out regime has been discussed. Analysis of the admittance peak, E1 together with the characteristic features in the frequency dependence of the conduction in freeze out regime suggest that conduction properties of the n-GaInNAsSb material in the freeze-out condition is governed by Mott's variable range hopping mechanism.