Admittance Spectroscopy on Irradiated GaAs Component Cells: Defect Analysis and Characterization

Temperature-dependent admittance spectroscopy is shown to be a valuable method to perform defect characterization in standardized 2 cm × 2 cm component cells, representative of the individual sub-cells in the triple-junction architecture GaInP/GaAs/Ge. The admittance spectra of the GaAs subcell irradiated with protons and electrons is analyzed in the range 90 K < T < 300 K. The signature of the irradiation-induced defect H1 is detected, located 0.29 eV above the valence band. An admittance model including the effect of a Gaussian-like distribution of defects in the band gap is adopted to fit the experimental data and to extract the electrical parameters of H1. Moreover, the signature of a second thermally-activated process is detected and ascribed to majority carrier transport over the barrier formed at the back-surface field region of the cell. A simple multi-conductance model is used to fit the measured admittance data and to extract the barrier height.