Abstract

The availability of femtosecond laser pulse provide new possibilities to investigate photocarrier dynamics under the influence of the surface space-charge field. Electron-hole pairs generated by laser pulse near semiconductor surface depletion layer move in such a way that band bending decreases, thereby affecting on such effects as optical second harmonic generation, electroreflection, terahertz radiation and other surface depending effects. The terahertz electromagnetic signal from semiconductor surface depletion region excited by femtosecond laser pulse is defined by the fast time-varying photocurrent caused by the spatial redistribution of photocarriers under the influence of surface space-charge field. At high phoexcitation level when photogenerated excess carrier concentration is comparable or greater than equilibrium carrier concentration the bandwidth of terahertz radiation is mainly defined by the time of screening of space-charge field.

© 1996 IEEE