Slow optical response of semi-insulating GaN film studied by terahertz emission and photoluminescence spectroscopy

We report the terahertz emission spectroscopy (TES) and photoluminescence (PL) spectroscopy results for a semi-insulating (SI) GaN film in comparison with those for unintentionally doped (UID) and magnesium (Mg)-doped ones. The TES and PL results showed notable slow changes on a time scale of approximately 10 s for the SI and UID GaN films, but not for the Mg-doped GaN film upon femtosecond ultraviolet laser illumination. The origin of the slow responses of the TES and PL spectra was studied by observing them under ambient air and vacuum conditions and attributed to hydrogen dissociation from GaN as a result of optical excitation.& nbsp;Published under an exclusive license by AIP Publishing.