Electrical and optical properties of radiation-induced dominant recombination center in In_xGa_1−xP space solar cells

We have performed detailed studies on the stability of the major irradiation-induced defect H2 in p-In_xGa_1−xP under various biases, in order to clarify the dependence of reaction rates on the position of the Fermi level in the absence of minority-carrier injection and electron-hole recombination. The dependence of the annealing rates on the electrical injection current has been analyzed at different temperatures by using a variety of electrical and optical experiments, such as deep-level transient spectroscopy, thermally stimulated capacitance, deep-level optical spectroscopy (DLOS), and photocapacitance (PHCAP). The energy of multiphonon emissions due to e-h recombination at the H2 center is estimated to be 1.36 eV. The capture cross section of the H2 trap for electrons under e-h recombination process is evaluated as σ_n=3×10⁻¹² cm², which is found to be significantly larger than the hole capture cross section (σ_p=1×10⁻¹⁶ cm²). The photoionization energy 0.94±0.10 eV is estimated by DLOS and confirmed by PHCAP experiments. The Frank-Condon shift value is estimated to be 0.45±0.10 eV. In order to fully explain the athermal annihilation mechanism of the H2 center under minority-carrier injection condition, a configuration coordinate diagram model has been proposed based on the measured physical parameters in this study.