Influence of V-Pits on the Turn-On Voltage of GaN-Based High Periodicity Multiple Quantum Well Solar Cells

Based on combined electrical analysis, microscopy investigation, and two-dimensional simulations we investigate the influence of V-pits on the turn-on voltage and current-voltage characteristics of high periodicity InGaN-GaN multiple quantum wells solar cells. Experimental measurements indicate that the sample with the thinnest p-GaN layer presents an early turn-on, which is not present for thicker p-GaN layers. Through technology computer aided design (TCAD) simulations, we show that the early turn-on is due to the insufficient V-pit planarization, as demonstrated by scanning electron microscopy and transmission electron microscopy analysis. V-pits penetrate the junctions, and locally put the quantum well region in closer connection with the p-side contact. The results provide insight on the role of V-pits on the electrical performance of high-periodicity quantum well devices, and demonstrate the existence of a trade-off between the need of a thin p-GaN (to limit short-wavelength absorption) and a thicker p-GaN, to favor V-pit planarization.