Monitoring interfacial dynamics by pulsed laser techniques. Final report

The research is aimed at understanding the structural, electronic, and reactive properties of semiconductors in solutions. Focus is on Si and GaAs surfaces because they are used in photovoltaic devices, etc. The pulsed laser techniques used included surface second harmonic generation in Si and laser induced photoluminescence in GaAs. SHG can measure space charge effects in the semiconductor under various conditions, ie, immersed in electrolyte, in presence of oxide overlayers, and under UHV conditions. The Si studies demonstrated the sensitivity of the phase of the SH response to space charge effects. With GaAs, time-correlated single photon counting methods were used in the picosecond time regime to examine the recombination luminescence following above band gap excitation (surface trapping velocities)