Recovery of Short Circuit Current of 3J Solar Cells by Current Injection at Low Temperature
InGaP/GaAs/Ge triple-junction (3J) solar cells designed for space applications were irradiated with 10 MeV protons at 3times1013 /cm2 at 210 K. Current at 0.25 A/cm2 was injected into the irradiated 3J solar cells after irradiation at 210 K to avoid the thermal annealing effects. The short circuit current (Isc) recovered with increasing current injection time, and the recovery saturated at current injection times above 1000 sec. The saturated Isc was 98% of the initial value. The defect annealing rate (A) was estimated to be between 0.003 and 0.01/s from the fitting of the current injection time dependence of the recovery of I sc
Deep Level Transient Spectroscopy Analysis of 10 MeV Proton and 1 MeV Electron Irradiation-Induced Defects in p-InGaP and InGaP-based Solar Cells
Minority carrier injection annealing under forward-bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of solar cells properties. Such peculiar recovery of properties affected by radiation damage demonstrates that InGaP-based devices, under minority-carrier injection-mode operation, have superior radiation resistance compared to GaAs and Si. The first example of a recombination-enhanced mechanism in the ternary compound InGaP is also reported. We have performed detailed studies of the stability of the radiation-induced defect H2 in p-InGaP under various biases in order to determine the dependence of the reaction rate on the position of the Fermi level in the absence of minority carrier injection and recombination. Recombination-enhanced defect annealing of H2 causes a reduction of the minority carrier injection annealing activation energy, compared to thermal annealing from 1.69 eV to 0.52 eV. Analysis of the results reveals that the mechanism involved in the minority carrier injection annealing of the defect is the energy release mechanism, in which enhancement is induced by the energy that is released when a minority carrier is trapped at the defect site.
Carrier removal in lattice-mismatched InGaP solar cells under 1-MeV-electron irradiation
Radiation-induced majority carrier removal is investigated from n+∕p− lattice-mismatched In0.56Ga0.44P solar cells under 1-MeV-electron irradiation. The change in carrier concentration in the 1×1017cm−3p− base layer is determined using standard capacitance–voltage techniques and found to proceed at a rate Rc=1.3cm−1, in agreement with that observed in lattice-matched InGaP. However, the observation of an increased short-circuit current and short-wavelength quantum efficiency over the unirradiated values at electron fluence levels in excess of 3×1015cm−2, allows the carrier concentration from the n+ emitter layer to be measured. By modeling the quantum efficiency of these solar cells, it is shown that the main photoresponse from these lattice-mismatched solar cells is due to drift transport, making the spectral response highly sensitive to changes in the width of the depletion region. Using this technique, the carrier concentration in the 2×1018cm−3 n+ emitter layer is found to be reduced to 1×1018cm−3 aft...