We report first band-offset measurements obtained by multiphoton internal-photoemission induced secondharmonic generation. Our two-color contactless laser technique involves ͑1͒ optically pumping electrons into the oxide and ͑2͒ probing the resulting interface electric field using time-dependent second-harmonic generation. One-and two-photon internal-photoemission thresholds for the Si/SiO 2 interface were measured to be 4.5 and 2.25 eV, respectively. This method promises to become a valuable experimental tool in determining band offsets in wide variety of semiconductor interfaces.
Effects of MgO deposition on Si∕SiO2 system and charge carrier trapping and recombination in Si∕SiO2∕MgO structures are studied using second-harmonic generation (SHG). An ultrafast 800nm laser was used both for multi-photon induced electron injection through the SiO2 into a potential well in the MgO, and for monitoring the time-dependent SHG signal, which is sensitive to the electric field at the Si∕SiO2 interface. Our results indicate that the MgO deposition introduces new trap states, and electrons trapped in the MgO transport more readily through the SiO2 than those in traps on the surface of SiO2. We attribute this to differences in trap energy levels and/or differences in process damage-induced defect densities in the SiO2.
Damage enhanced electron transport, across thin oxides in x-ray irradiated Si/SiO 2 samples, was measured via a contactless two-color laser technique. This method involves two steps: ͑1͒ optically stimulated electron injection into the oxide and ͑2͒ detection of transport, trapping, and recombination rates using time-dependent electric-field-induced second-harmonic generation arising from charge separation at the interface. Measured electron transport rates across an irradiated oxide are found to be substantially higher in comparison to unirradiated oxides. This effect is attributed to the presence of x-ray irradiation-induced defects that act as intermediate trapping sites facilitating enhanced electron tunneling through the oxide. The possible nature of the radiation-induced trapping sites is discussed.
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