Abstract
We excite GaN compound semiconductor by using the Ti: sapphire pulse laser as the pumping source so that we could observe the nonlinear absorption phenomenon, and hence the band structure of GaN. The wavelength of the Ti: sapphire pulse laser is 800 nm, unit peak power could be 81.25 KW. After chirped-pulse amplification, its wavelength is still 800nm, but unit peak power could reach 4.62 GW. First we use He-Cd laser (325nm) to excite n-GaN sample with variable pump power and temperature. The photoluminescence we got correspond to the band-edge structure of GaN. The PL spectrum of GaN should has the dependence of polarization of E-filed in theory, but we couldn’t observe that phenomenon. It maybe due to Si-doped induced merge of band structure. For comparing, we also do experiment of unintentially-doped GaN, and with these data we could try to understand the mechanism of the carrier recombination in these two sample, both are dominated by donor-bound excitons. Alternatively, we use the pulse laser to excite GaN sample and thus have a PL spectrum looks like the linear excited one, but with a thinner spectrum width. Besides, using pulse-laser excitation, we could extract the power dependence (cubic) between the intensity of pumping laser and PL signal, and it shows that the photoluminescence is due to the 3-photon absorption of GaN.