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

摘要

Bias dependence of the admittance spectroscopy of GalnNAsSb 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 GalnNAsSb (n-GalnNAsSb) layer in the structure. From the zero bias admittance spectrum, three peaks namely El, El, and E3 corresponding to the localized level at 0.03 eV, 0.07 eV, and 0.16 eV below the conduction band edge (E_C) of n-GalnNAsSb material, respectively, were found. Constant position of ￡2 and ￡3 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- GalnNAsSb film. However, bias dependence admittance of the El peak along with the capacitance - voltage (C-V) measurement as well as characteristic feature in the temperature dependent junction capacitance value strongly - suggests that El peak might be originated due to the free carrier relaxation in the n- GalnNAsSb layer in lower temperature. Conduction mechanism in the freeze-out regime has been discussed. Analysis of the admittance peak, El together with the characteristic features in the frequency dependence of the conduction in freeze out regime suggest that conduction properties of the n-GalnNAsSb material in the freeze-out condition is governed by Mott's variable range hopping mechanism.