Effects of Background Zn Doping on the Performance of InGaAs/GaAsP Multiple Quantum Well Solar Cells Grown by a Planetary Metal Organic Vapor Phase Epitaxy Reactor

Abstract

The effects of background Zn doping on the performance of p–i–n GaAs solar cells with InGaAs/GaAsP multiple quantum wells (MQWs) in i-GaAs layer have been studied. The crystal growth was done by a planetary metalorganic vapor phase epitaxy (MOVPE) reactor. The background Zn doping, in an order of 1017 cm-3, degraded the solar cell efficiency by modifying the energy band diagram in a way that obstructed carrier transports. It was shown by calculation that the carrier transports across the MQWs region suffered from decrease in built-in electric field in absorber layers, leading to an efficiency loss by radiative and nonradiative recombinations. Consequently, the external quantum efficiency and the current density of a Zn-contaminated MQW solar cell were terribly poor. Reactor baking at 850 °C for 20 min seems to remove Zn residues effectively without noticeable effects on the succeeding growth of MQW solar cells. The InGaAs/GaAsP MQWs fabricated in the thermally cleaned reactor have shown a potential to extend the absorption edge of GaAs solar cells and to improve the efficiency of multi-junction solar cells by current matching. Therefore, the growth of InGaAs/GaAsP MQWs by planetary MOVPE reactors requires a careful treatment regarding the background doping issue.