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In recent years, the development of cadmium zinc telluride (CdZnTe) detectors for x-ray and gamma ray spectrometry has grown rapidly. The good room temperature performance and the high spatial resolution of pixellated CdZnTe detectors make them very attractive in space-borne x-ray astronomy, mainly as focal plane detectors for the new generation of hard x-ray focusing telescopes. In this work, we investigated on the spectroscopic performance of two pixellated CdZnTe detectors coupled with a custom low noise and low power readout application specific integrated circuit (ASIC). The detectors (10×10×1 and 10×10×2 mm3 single crystals) have an anode layout based on an array of 256 pixels with a geometric pitch of 0.5 mm. The ASIC, fabricated in 0.8 μm BiCMOS technology, is equipped with eight independent channels (preamplifier and shaper) and characterized by low power consumption (0.5 mW/channel) and low noise (150–500 electrons rms). The spectroscopic results point out the good energy resolution of both detectors at room temperature [5.8% full width at half maximum (FWHM) at 59.5 keV for the 1 mm thick detector; 5.5% FWHM at 59.5 keV for the 2 mm thick detector) and low tailing in the measured spectra, confirming the single charge carrier sensing properties of the CdZnTe detectors equipped with a pixellated anode layout. Temperature measurements show optimum performance of the system (detector and electronics) at T=10 °C and performance degradation at lower temperatures. The detectors and the ASIC were developed by our collaboration as two small focal plane detector prototypes for hard x-ray multilayer telescopes operating in the 20–70 keV energy range. [ABSTRACT FROM AUTHOR]

Presents a study which determined the Si-SiO[sub2] interface defects produced as a result of negative bias, high-field electron injection into the SiO[sub2] layer of metal-oxide-semiconductor capacitors. Source of interface traps in unannealed SiO[sub2] on silicon; Details of electron paramagnetic resonance experiments on the Si-SiO[sub2] system.

New features in electron paramagnetic resonance (EPR) of porous silicon have been examined here. A new isotropic EPR center was observed at g=1.9995(1) at T=4.2 K, in both p-type and n-type porous silicon. By comparing its g value with those of shallow donors in bulk silicon, the center was identified due to the conduction-band (CB) electrons in silicon microcrystals. The CB signal, present in freshly prepared p-type and n-type samples, can be dramatically and surprisingly enhanced by the presence of a polar solvent on the n-type porous silicon surface. Even though it was shown that most of the donor electrons in an n-type sample can be pulled into the porous layer from the substrate by solvent exposure of the porous layer, the possible electrochemical effects are not yet completely understood; to establish a reasonable model for them would require appropriately controlled experiments. [ABSTRACT FROM AUTHOR]

Current-voltage (I-V) characteristics of Schottky Al/p-CdTe/Pt detectors were investigated in dark and at different temperatures. CdTe detectors with Al rectifying contacts, very appealing for high resolution x-ray and gamma ray spectroscopy, suffer from bias-induced polarization phenomena which cause current increasing with the time and severe worsening of the spectroscopic performance. In this work, we studied the time-dependence of the I-V characteristics of the detectors, both in reverse and forward bias, taking into account the polarization effects. The I-V measurements, performed at different time intervals between the application of the bias voltage and the measurement of the current, and the measured current transients show as the electrical instability manifests itself even in time intervals shorter (i.e., <1 s) than those are necessary to make evident the degradation of the spectroscopic properties. The results point out as this time interval is a critical parameter for correct investigations on the electrical properties of these devices. Although the detectors are typically classified as Schottky-type detectors, we find that the thermionic emission is not the dominant transport mechanism, except at very low bias voltage values. Finally, the Schottky barrier height of the Al/p-CdTe contact was extracted by measuring the contact resistance at zero bias. [ABSTRACT FROM AUTHOR]