Annual Meeting of the American Physical Society, March 1999, Atlanta,


Session IC33 - Electron & Photon Induced Excitations at Surfaces.
ORAL session, Tuesday morning, March 23
Room 162W, GWCC


[IC33.09] Study of carrier dynamics near GaAs surface using time-resolved second-harmonic generation

Keng-Chang Chou, Harry W.K. Tom (Department of Physics, University of California, Riverside)

We have studied the dynamics of photoexcited carriers near the n-type GaAs (110) surface by time-resolved second harmonics generation (SHG). A 20 fs laser pulse (840 nm, 88 MHz) generated carriers in the GaAs, and the SHG from a second time-delayed probe beam was detected. By properly choosing the GaAs crystal orientation, we are able to measure the DC-field induced SH susceptibility and reject the bulk dipole-allowed SH. A 90 percent SHG signal decrease was observed due to the field screening by the injected carriers. Due to its short probing depth, SHG provides a highly sensitive tool to study the carrier dynamics near the surface,^[1,2] compared with previous studies using visible^[3] or IR^[4] reflection and transmission. A diffusion model was used to provide quantitative evaluation of carrier recombination time and surface recombination velocity. \$ [1] J. Qi \textitet al., Phys. Rev. Lett., vol. 71, 633 (1993) \$ [2] A. Nahata and T. F. Heinz, Appl. Phys. Lett., vol. 69, 746 (1996) \$ [3] T. Dekorsy, T. Pfeifer, W. Kutt, and H. Kurz, Phys. Rev. B, vol. 47, 3842 (1992) \$ [4] R. S. Miranda, H. W. K. Tom, A. M. Johnson, T. J. Bridges, and G. D. Aumiller, Appl. Phys. Lett., vol. 60, 1105 (1992)