Nonlinear Optical Techniques for Characterization of Wide Bandgap Semiconductor Electronic Properties: Ⅲ-nitrides, SiC, and Diamonds

摘要

Combining interdisciplinary fields of nonlinear optics, dynamic holography, and photoelectrical phenomena, we developed the optical measurement technologies for monitoring the spatial and temporal non-equilibrium carrier dynamics in wide bandgap semiconductors at wide range of excitations (10~(15) to 10~(20) cm~(-3)) and temperatures (10 to 800 K). We explored advantages of non-resonant optical nonlinearities, based on a short laser pulse induced refractive or absorption index modulation (△n and △k) by free excess carriers. This approach, based on a direct correlation between the electrical and optical processes, opened a possibility to analyze dynamics of electrical phenomena in "all-optical" way, i.e. without electrical contacts. Carrier diffusion and recombination processes have been investigated in various wide band gap materials - differently grown GaN, SiC, and diamonds - and their key electrical parameters determined, as carrier lifetime, diffusion coefficient, diffusion length and their dependences on temperature and injected carrier density. The studies provided deeper insight into nonradiative and radiative recombination processes in GaN crystals, revealed diffusion-driven long nonradiative carrier lifetimes in bulk GaN and SiC, disclosed impact of delocalization in InGaN layers, and suggested a trap-assisted Auger recombination in highly-excited InN. Injection and temperature dependent diffusivity revealed a strong contribution of carrier-carrier scattering in diamond and bandgap renormalization in SiC.