Percorrer por autor "Schwarz, Reinhard"
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- Laser-scanned p-i-n photodiode (LSP) for image detectionPublication . Vieira, Manuela; Fernandes, Miguel; Martins, João; Louro, Paula; Maçarico, António Filipe Ruas Trindade; Schwarz, Reinhard; Schubert, Markus B.Amorphous and microcrystalline glass/ZnO:Al/p(a-Si:H)/i(a-Si:H)/n(a-Si1 C :H)/Al imagers with different n-layer resistivities were produced by plasma-enhanced chemical vapor deposition technique (PE-CVD). The transducer is a simple, large area p-i-n photodiode; an image projected onto the sensing element leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The effect of the image intensity on the sensor output characteristics (sensitivity, linearity, blooming, resolution, and signal-tonoise ratio) are analyzed for different material composition. The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity and on the spatial resolution is achieved with a responsivity of 0.2 mW/cm2 by decreasing the -layer conductivity by the same amount. In a 4 4 cm2 laser-scanned photodiode (LSP) sensor, the resolution was less than 100 m and the signal-to-noise (S/N) ratio was about 32 dB. Aphysical model supported by electrical simulation gives insight into the methodology used for image representation.
- New p-i-n Si : H imager configuration for spatial resolution improvementPublication . Vieira, Manuela; Fernandes, Miguel; Martins, João; Louro, Paula; Maçarico, António Filipe Ruas da Trindade; Schwarz, Reinhard; Schubert, Markus B.Amorphous glass/ZnO-Al/p(a-Si:H)/i(a-Si:H)/n(a-Si1-xCx:H)/Al imagers with different n-layer resistivities were produced by plasma enhanced chemical vapour deposition technique (PE-CVD). An image is projected onto the sensing element and leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout, and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The influence of the intensity of the optical image projected onto the sensor surface is correlated with the sensor output characteristics (sensitivity, linearity blooming, resolution and signal-to-noise ratio) are analysed for different material compositions (0.5 < x < 1). The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity signal and on the spatial resolution are achieved at 0.2 mW cm(-2) light flux by decreasing the n-layer conductivity by the same amount. A physical model supported by electrical simulation gives insight into the image-sensing technique used.
- Non-linear optical spontaneous photoluminescence emission enhancement effect in wide gap gallium nitride thin filmsPublication . Niehus, Manfred; Schwarz, ReinhardWith two interfering pulses from the 4th harmonic of a Nd-YAG laser we burnt a periodic lattice structure into the surface of GaN thin films. The lattice period of this permanent grating could be controlled between less than one and several tens of microns. Above the decomposition threshold, nitrogen evades from the sample surface, and the residual metallic gallium accumulates in the form of tiny droplets at the surfaces. The patterned structure shows structural similarities with microcavities. The question arises if the residual metallic gallium may act as a partially reflecting mirror. To test this hypothesis, we studied the steady-state and transient photoluminescence through the modulation of light emerging from the ubiquitous broad “yellow” photoluminescence band. The microlattice shows up by energy-equidistant spontaneous emission enhancement peaks in the steady-state photoluminescence spectra. We suggest that the partial reflection due to the residual metallic gallium leads to the observed enhancement effect.