Femtosecond optical spectroscopy studies of high-pressure-grown (Al,Ga)N single crystals

We present our time-resolved studies of the carrier dynamics in high quality Al0.86Ga0.14N single crystals, grown using a solution technique in a high nitrogen gas pressure autoclave. Our optical measurements were performed using a femtosecond, pump-probe spectroscopy, by invoking the two-photon-absorption-type process and scanning the normalized transient differential transmissivity signal (Delta T/T) of the probe beam. Our time-resolved Delta T/T photoresponse consisted of a Gaussian-shape correlation signal with the pulse width of similar to 300 fs, which in two-color experiments was followed by a bi-exponential hot-electron relaxation transient. By plotting the autocorrelation signal amplitude versus the total energy of the absorbed pump and probe photons, we were able to very accurately determine the optical bandap of Al0.86Ga0.14N, as equal to 5.81 +/- 0.01 eV.