III-nitride-based photovoltaic applications on silicon: Comparison between axial and coreshell InGaN nanowire devices
Résumé
Solar cells are one of the major source of renewable energy available today. InGaN alloys are promising candidates for future solar cells due to their direct tunable bandgap between 0.7 eV and 3.4 eV, covering major absorption range of solar spectrum. However, the conversion efficiency of InGaN-based solar cells remains limited because of the poor crystalline quality of thick InGaN layers, particularly at high indium composition. In this work, to overcome this limit, we propose two structures based on InGaN core?shell and axial InGaN nanowires. We performed the hydride vapor phase epitaxy (HVPE) to directly grow n-type GaN wires and InGaN nanowires on p-type silicon substrate. The metalorganic vapor phase epitaxy (MOCVD) was applied to grow the InGaN core?shell structure. The energy dispersive X-ray spectroscopy (EDS) and cathodoluminescence measurements revealed that nanowires grown on silicon exhibit an uniform indium distribution of ~ 40?50 %, with an ideal bandgap configuration of InGaN 1.8 eV/Si 1.12 eV for high conversion efficiency. Then, the photovoltaic properties of the fabricated solar cells were assessed. As a consequence, short-circuit current density and open-circuit voltage were typically ~20 µA/cm2 and 0.1 V under a 1 sun (1.5 AMG) illumination, respectively. Even though, the efficiency measured was still low, this work suggests the potential of directly integrated InGaN nanowires on silicon for solar cell applications.