Dynamics of Below-Band-Gap Carrier in Highly Excited GaN
GUO Bing1,2, WONG Kam-Sing1, YE Zhi-Zhen2, JIANG Hong-Xing3, LIN Jing-Yu3
1Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
2State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027
3Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601, USA
Dynamics of Below-Band-Gap Carrier in Highly Excited GaN
1Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
2State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027
3Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601, USA
Abstract： Femtosecond time-resolved reflectivity was used to investigate below-band-gap (3.1 eV) carrier dynamics in a nominally undoped GaN epilayer under high excitation. A 2.5-ps rising process can be observed in the transient trace. This shot rising time results from the hot phonon effects which can cause a delayed energy relaxation of the initial photocarriers toward the band edge. From the density dependence of the carrier dynamics, the Mott density was estimated to be 1.51-1.56 x 1019cm-3. Below the Mott density, the initial probed carrier dynamics was explained to the effect of acoustic phonon-assisted tunneling for localized states, where a significant excitation density dependence of the tunneling probability was observed due to the optically-induced bandtail extension to lower energies. Above the Mott density, the measured carrier dynamics reflected the relaxation of an electron-hole plasma, in which a distinct fast decay component of 2.3 ps was observed due to the onset of nonlinear relaxation processes such Auger recombination.
2003, Vol. 20 
