Abstract
We have studied surface defect states and conduction electrons in molecular-beam epitaxy (MBE)-grown and metalorganic vapor phase epitaxy (MOVPE)-grown GaN films using the third and fourth harmonics of a Ti:sapphire pulsed laser to excite photoelectrons by one- and two-photon transitions. By introducing a delay between the excitation and probe pulses in two-step excitations it is possible to measure the intermediate state lifetimes. Spectra of occupied surface defect states in the gap of n-type GaN are reported. Under intense photon pumping, conduction electron spectra are observed. The relaxation time of hot carriers in the conduction band is less than 200 fs.
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