GaN characterizations using femtosecond optical pulses

Summary form only given. The demonstration of high-brightness green-UV light-emitting diodes and laser diodes has established GaN as key materials for optoelectronics operating in the green-UV wavelength range. Despite the progress in the device developments, the basic properties of GaN are still poorly understood. Due to their high peak powers and short pulse widths, femtosecond optical pulses have become major tools for material characterization. We report on the characterization of GaN using femtosecond optical pulses. First, we have measured below bandgap nonlinear refractive index n/sub 2/ using Z-scan techniques. High n/sub 2/ value on the order of -10/sup -12/ cm/sup 2//W was measured, which indicates potential applications in all optical control and ultrafast optoelectronics. Second, we have measured two photon absorption coefficient (/spl beta//sub 2/) using pulsewidth autocorrelation. The measured /spl beta//sub 2/ is on the order of 3 cm/GW (for midgap wavelengths), which is higher than that of diamond and one order of magnitude larger than that of fused silica. The large two-photon absorption coefficients and broad band applicability make GaN and related materials excellent candidates as nonlinear crystals for IR-UV femtosecond pulsewidth measurements. Third, using femtosecond thermomodulation spectroscopy, we have studies the bandtail states in heavily n-typed doped GaN samples.