Electronic Properties of Energetic Particle-Irradiated In-rich InGaN Alloys

InGaN alloys, whose fundamental bandgaps span almost perfectly the solar spectrum, are potential materials for high-efficiency tandem solar cells. We have carried out a systematic study on the effect of irradiation on the electronic and optical properties of InGaN alloys over the entire composition range. Three different types of energetic particles (electrons, protons, and alpha particles) were used to produce displacement damage doses ($D_{d})$ spanning five orders of magnitude. The electron concentrations in InN and In-rich InGaN increase with $D_{d}$ and finally saturate after a sufficiently high dose of irradiation. The saturation of carrier density is attributed to the Fermi level pinning at the Fermi Stabilization Energy ($E_{FS})$, as predicted by the amphoteric native defect model. Electrochemical capacitance-voltage (ECV) measurements reveal a surface electron accumulation whose concentration is determined by pinning at E$_{FS}$. Modeling with a combination of various scattering mechanisms provides an excellent fit with the mobility measurements.