A comparison of hydrogen passivation in heteroepitaxial n+ p and p+n solar cells

Hydrogen passivation of MOCVD-grown heteroepitaxial InP space solar cell structures with both n⁺p and p⁺n configurations are compared and the different passivation characteristics are investigated. A 2 hour exposure to a 13.56 MHz hydrogen plasma at 250°C reduces the deep level concentration in the base regions of both n⁺p and p⁺n heteroepitaxial InP cell structures from as-grown values near 1×10 cm^-3, down to the 2-5×10¹² cm^-3 range, resulting in significant reductions in reverse leakage current for both configurations. All dopants were successfully reactivated by a 400°C, 5 minute anneal with no detectable activation of deep levels. Passivation of both structures are stable to >500°C. I-V characteristics demonstrate significant differences in the voltage behavior of the two cell configurations, with a ~280 mV increase in built-in voltage for p⁺n cells and no corresponding change for n⁺p cells. This enhancement in V_bi is attributed to complex interactions between Zn, H and extended defects within the heavily doped emitter