ENHANCED CARRIER COLLECTION EFFICIENCY IN InGaAs/GaAsP QUANTUM WELL SOLAR CELLS BY COMPENSATION DOPING

摘要

The major challenge of multiple quantum wells (MQWs) solar cells is to sufficiently extract photoexcitedcarriers to the external circuit at the operation voltage through MQWs regions. The present study reports theeffectiveness of compensation doping of the i-region, which includes MQWs, for more efficient transport of bothelectrons and holes. P-type unintentional doping exists in GaAs by inevitable carbon incorporation during MOVPE,causing undesired bending of the band-lineup in the i-region. By cancelling this out with n-type dopants, sulfur, wehave achieved much high carrier collection efficiency of >90% at the operation bias voltage regardless of theexcitation wavelength, compared to <50% without compensation doping treatment. As a result, the cell performancewas greatly improved, especially showing an enhanced FF from 0.54 to 0.77, and the degradation-free QE withinGaAs absorption wavelength range. The bias dependent PL analysis showed that PL intensity increased as the CCEdecreases at a large forward bias, and that the radiative recombination loss was significantly suppressed bycompensation doping. Furthermore, time-resolved PL study indicated much faster speed of carrier escape from thewells, showing a quicker PL decay time of 7 ns at 0.6 V, compared to 18-51 ns without compensation doping.