Electrical and optical properties of radiation-induced dominant recombination center in InxGa1-xP space solar cells

We have performed detailed studies on the stability of the major irradiation-induced defect H2 in p-InxGa1-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 1.36eV. The capture cross section of the H2 trap for electrons under e-h recombination process is evaluated as σn=3×10- 12cm2, which is found to be significantly larger than the hole capture cross section (σp=1×10-16cm2). The photoionization energy 0.94±0.10eV is estimated by DLOS and confirmed by PHCAP experiments. The Frank-Condon shift value is estimated to be 0.45±0.10eV. 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.