Percorrer por autor "Schwarz, R."
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- Photocapacitance measurements in irradiated a-Si:H based detectorsPublication . Schwarz, R.; Mardolcar, U.; Vygranenko, Y.; Vieira, M.; Casteleiro, C.; Stallinga, Peter; Gomes, Henrique L.Photocapacitance measurements were performed on amorphous silicon p–i–n detectors before and after particle irradiation with 1.5 MeV 4 He+ ions. The spatial resolution across a degraded spot is similar to the one obtained in photocurrent scans and is of the order of the diameter of the scanning laser beam. We monitored the transient capacitance after applying short laser pulses to deduce trap energies of 0.64 eV. Photocapacitance measurements as a function of the applied bias, the measurement frequency up to 1 MHz, and the wavelength of laser light are discussed. The reduction in photocapacitance signal and the shift of the cut-off frequency after ion bombardment are correlated with the change in transport properties.
- Spatially-resolved photocapacitance measurements to study defects in a-Si:H based p-i-n particle detectorsPublication . Casteleiro, C.; Schwarz, R.; Mardolcar, U.; Maçarico, A.; Martins, J.; Vieira, M.; Wuensch, F.; Kunst, M.; Morgado, E.; Stallinga, Peter; Gomes, Henrique L.Thick large-area particle or X-ray detectors suffer degradation during operation due to creation of defects that act as deep traps. Measuring the photocurrent under homogeneously absorbed weak light can monitor variation in detector performance. We describe how photocapacitance can be used as an alternative method to measure the creation of defects and their energy level after intense irradiation with protons or He ions at 1.5 MeV and after exposure to intense laser pulses. The possibility to detect small areas of high defect density in a large-area detector structure is discussed.
- Study of trap states in zinc oxide (ZnO) thin films for electronic applicationsPublication . Casteleiro, C.; Gomes, Henrique L.; Stallinga, Peter; Bentes, L.; Ayouchi, R.; Schwarz, R.The electrical properties of ZnO thin films grown by pulsed laser deposition were studied. Field-effect devices with a mobility reaching 1 cm2/V s show non-linearities both in the current–voltage and in the transfer characteristics which are explained as due to the presence of trap states. These traps cause a reversible threshold voltage shift as revealed by low-frequency capacitance–voltage measurements in metal insulator semiconductor (MIS) capacitors. Thermal detrapping experiments in heterojunctions confirm the presence of a trap state located at 0.32 eV.