Optimization of the p-GaN window layer for InGaN/GaN solar cells

In this work we report on the optimization of the p-GaN window layer for InGaN/GaN solar cells. We studied the effect of p-GaN thickness and growth temperature on the electrical performance. By optimizing the window thickness of In_xGa_1-xN solar cells with X_In ≈ 0.04 we maximized short wavelength response and produced solar cells with 82% FF and Voc of 2 V and enhancement of Jsc of 80% over un-optimized devices. We also studied the effect of growth temperature of the window layer, and found that the electrical performance was greatly improved with higher growth temperatures. By increasing the p-GaN growth temperature from 890°C to 1040°C, reverse bias leakage was reduced by three orders of magnitude, Voc increased from 0.85 to 1.65 V and peak output power increased by nearly 100% for devices with X_In ≈ 0.08. Surface pit density was also significantly decreased by increasing growth temperature and seems to be an important mechanism for leakage in these devices.