Nonlinear Optical Techniques for Characterization of Wide Bandgap Semiconductor Electronic Properties: III-nitrides, SiC
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Nonlinear Optical Techniques for Characterization of Wide Bandgap Semiconductor Electronic Properties: III-nitrides, SiC, and Diamonds Kęstutis Jarašiūnas1, 2, Ramūnas Aleksiejūnas1,Tadas Malinauskas1, Saulius Nargelas1, and Patrik Ščajev1 1 Department of Semiconductor Optoelectronics, Institute of Applied Research, Vilnius University, Saulėtekio al. 9-III, Vilnius, LT-10222 Lithuania 2 Department of Electrical and Computer Engineering, Virginia Commonwealth University, 601 W. Main Str., Richmond, Virginia 23284 USA ABSTRACT 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 (1015 to 1020 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 (Δn and Δk) 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 diffusiondriven long nonradiative carrier lifetimes in bulk GaN and SiC, disclosed impact of delocalization in InGaN layers, and suggested a trap-assisted Auger recombination in highlyexcited InN. Injection and temperature dependent diffusivity revealed a strong contribution of carrier-carrier scattering in diamond and bandgap renormalization in SiC. INTRODUCTION During the last two decades, a significant progress in growth techniques paved a way for development of novel device-quality wide bandgap semiconductors. The most prominent among them are III-nitrides [1], silicon carbide [2], and diamond [3], all featuring some superior characteristics for high power optical or electronic devices. Unfortunately, growth of these materials up to now remains challenging, which inevitably leads to relatively high defectiveness of the layers. Point and extended defects affect the dynamics of excess carriers, hence degrading performance and reliability of devices. In spite of a huge experimental and theoretical effort, many peculiarities of carrier recombination and transport processes remain unclear; especially this is true for highly excited semiconductors, when conditions are similar to those in operating high power devices. In this article, we address this problem in III-nitride, SiC, and diamond semiconductors by using two pump-probe optical techniqu
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