Improved dark current characteristics of GaAs/InGaAs multi-quantum well solar cells fabricated by atomic H-assisted molecular beam epitaxy

The authors have fabricated shallow and deep InGaAs/GaAs multi-quantum well (MQW) solar cell diodes by atomic H-assisted molecular beam epitaxy (H-MBE) and the conventional MBE. The measured dark currents in H-MBE diodes were found to be 1~2 orders of magnitude smaller than in MBE for both MQW and p-i-n diodes. This was due to the effect of defect passivation by H-atoms. The temperature dependence of dark currents were also characterized in order to determine the upper limit of potential depth for the photo-generated carriers to escape efficiently out of the quantum well and thereby minimize the recombination currents at the MQW heterointerfaces. It was concluded that for a given 10-period InGaAs/GaAs MQW diode, In composition should be set <~0.1