Charge emission from silicon and germanium surfaces irradiated with KrF excimer laser pulses

The authors report time-resolved measurements of the emission of positive and negative charge from Si and Ge surfaces irradiated with 248-nm KrF excimer laser pulses. With pulse energies both below and above the melting threshold, the time evolution of the emission currents is complex and strikingly different for Si and Ge. The positive ion emission signal from Ge persists only for the duration of the laser pulse (<60 ns), but in sharp contrast, the signal from Si continues for several microseconds. A tentative suggestion is made that the positive ions encounter a Knudsen layer created just above the surface of the Si target. More refined experiments, coupled with a theoretical effort, are proposed.