Transient Absorption Spectroscopy Reveals Dynamics of Electrons and Holes in GaN

The TAS (Transient Absorption Spectroscopy) technique was used to excite the GaN sample at 650 nm using two-photon excitation. This allowed for the generation of a low and uniform excess carrier density, eliminating surface recombination and carrier diffusion effects. The linear absorption spectrum and Z-scan data of the GaN sample were analyzed.

The two-photon absorption coefficient (b) at 650 nm was determined to be 5.1 cm/GW. The PL spectra of the GaN sample showed a YL band with a peak at around 2.2 eV. Under two-photon excitation, a bright YL band was observed in the GaN sample, indicating the presence of the CN defect.

The TAS in sample 02Ge showed that the TA signal increased with the probe wavelength after excitation. No additional absorption peaks were observed, which is characteristic of free-carrier absorption (FCA). The TA can be attributed to the indirect absorption of electrons and holes in the conduction band (CB) and valence band (VB).

The dynamics of both electrons and holes were monitored using a probe at 850 nm, while a probe at around 1050 nm allowed for the monitoring of the instantaneous hole density. The TA kinetics probed at 850 and 1050 nm were analyzed.