Influence of Indium Content on the Unintentional Background Doping and Device Performance of InGaN/GaN Multiple-Quantum-Well Solar Cells

We experimentally investigate the influence of indium composition on the photovoltaic performance of InGaN/GaN multiple-quantum-well (MQW) solar cells. Three MQW structures with different In content are grown via metal-organic chemical vapor deposition, and then fabricated into solar cell devices. The solar cells with lower In content show stronger photovoltaic response, which may be ascribed to both smaller piezoelectric fields in InGaN well layers and better material quality of MQW active region. In addition, based on the capacitance-voltage measurements by which the profiles of apparent carrier concentration can be determined, we find that in the higher-In-content solar cells the background electron concentration in unintentionally doped InGaN QWs is higher. Consequently, the effective volume of active region, or the width of depletion region, may become smaller at zero bias and correspondingly the light absorption by InGaN active layers is reduced. This may be attributed to the increased nitrogen vacancy-related defects which are easier induced into In-rich InGaN alloys as a source of shallow donors.