Direct Auger recombination and density-dependent hole diffusion in InN

Indium nitride has a good potential for infrared optoelectronics, yet it suffers from fast nonradiative recombination, the true origin of which has not been established with certainty. The diffusion length of free carriers at high densities is not well investigated either. Here, we study carrier recombination and diffusion using the light-induced transient grating technique in InN epilayers grown by pulsed MOCVD on c-plane sapphire. We show that direct Auger recombination governs the lifetime of carriers at densities above ~10¹⁸ cm^-3. The measured Auger recombination coefficient is (8 ± 1) × 10^-29 cm^-3. At carrier densities above ~5 × 10¹⁹ cm^-3, we observe the saturation of Auger recombination rate due to phase space filling. The diffusion coefficient of holes scales linearly with carrier density, increasing from 1 cm²/s in low-doped layers at low excitations and up to ~40 cm²/s at highest carrier densities. The resulting carrier diffusion length remains within 100-300 nm range, which is comparable to the light absorption depth. This feature is required for efficient carrier extraction in bipolar devices, thus suggesting MOCVD-grown InN as the material fit for photovoltaic and photonic applications.