Characterization of GaInP/Ge heterostructure solar cells by capacitance measurements at forward bias under illumination

The n-GaInP/n-p Ge heterostructure sloar cells grown by OMVPE were studied by new technique based on the diffusion capacitance measurements under illumination at open circuit voltage conditions. The value of the effective minority carrier lifetime in the p-Ge base tau(eff)=1.5x10(-6) s was determined from the frequency dependence of the diffusion capacitance, C(f). The numerical simulation model was developed, which is in a good agreement with the experimental C(f), capacitance-voltage and dark current-voltage measurements. The value of the bulk minority lifetime equal to tau(b)= 5x10(-6) s was obtained by the simulation fit of the experimental data. The simulations have also demonstrated that the diffusion capacitance is very sensitive to the recombination velocity at the back contact, (Sbc), for S-bc<10(5) cm/s providing a way to characterize the back contact quality. Thus the proposed technique could be very useful for the back surface passivation development in GaInP/Ge solar cells. (C) 2011 Published by Elsevier B. V.