A.A. Turturici

Time-dependent current-voltage characteristics of Al/p-CdTe/Pt x-ray detectors

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., <1u2009s) 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...

Charge carrier transport mechanisms in CdZnTe detectors grown by the vertical Bridgman technique

In this work, we report on the results of electrical characterization of CdZnTe (CZT) detectors, with gold electroless contacts, grown by the boron oxide encapsulated vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with different thicknesses (1 and 2.5 mm), have the same electrode layout: the anode is a central electrode (2 × 2 mm2) surrounded by a guard-ring electrode. The cathode is a planar electrode covering the detector surface (4.1 × 4.1 mm2). Current-voltage (I-V) characteristics were measured at different temperatures in order to study the charge transport and the electrical properties. These detectors were compared with the traveling heater method (THM) CdZnTe grown detectors (Redlen, Canada), fabricated with the same electrode layout and deposition. The results highlight the low leakage currents of the B-VB CdZnTe detectors even at high bias voltages: 38 nA/cm2 (T = 25°C) at 10000 V/cm. This feature allows high bias voltage operation, very important for high flux applications. These activities are in the framework of an Italian research project on the development of energy-resolved photon counting (ERPC) systems for high flux energy-resolved X-ray imaging.

The ″Livio Scarsi″ X-ray Facility at University of Palermo for device testing

In this work, we report on the characteristics of the Livio Scarsi X-ray facility at University of Palermo. The facility is able to produce low energy X rays, within the energy range of 0.1-60 keV, with fluence rates ranging from 105-108 photons/mm2 s. The laboratory is equipped with an innovative digital detection system, based on semiconductor detectors (Si and CdTe detectors), able to provide accurate and precise estimation of the fluence rate, the energy and the exposure of X rays, even at high counting rate conditions. Instrumentation for electrical characterization (DC-AC) of semiconductor devices, for both off-line and on-line (i.e. during the irradiation) measurements, is also available. Total ionizing dose (TID) tests on rad-hard power MOSFET transistors by using both X rays and 60Co gamma rays are presented. The aim of this work is to open up to potential users for low energy X-ray applications.

Characterization of Al-Schottky CdTe detectors

In the last decades, great efforts are being devoted to the development of CdTe detectors for high resolution X-ray and gamma ray spectroscopy. Recently, new rectifying contacts based on aluminum (Al) are very appealing in the development of CdTe detectors with low leakage currents and anode pixellization. In this work, we report on preliminary results of electrical and spectroscopic investigations on Schottky CdTe diode detectors (4.1 × 4.1 × 0.75 and 4.1 × 4.1 × 2 mm3) with Au/Ti/Al/CdTe/Pt electrode configuration. The detectors are characterized by very low leakage currents even at room temperature (26 pA at 25 °C under a bias voltage of −100 V for the 2 mm thick detector). Polarization phenomena, typical of CdTe diode detectors, were investigated through electrical and spectroscopic approaches, pointing out the influence of the bias voltage, the temperature and the detector thickness. Good time stability, during a short-term operation of one hour, was observed for both detectors at temperatures below 10 °C and by using an electric field of 5000 V/cm. The detectors exhibited good energy resolution of 1.5 keV (FWHM) at 59.5 keV (T=−25 °C) by using a standard electronic chain. This work was carried out in the framework of the development of portable X-ray spectrometers for both laboratory research and medical applications.

Spectroscopic response and charge transport properties of CdZnTe detectors grown by the vertical Bridgman technique

In this work, we present the results of spectroscopic investigations on CdZnTe (CZT) detectors grown by the boron oxide encapsulated vertical Bridgman technique (IMEM-CNR, Parma, Italy). The detectors, with different thicknesses (1 and 2.5 mm), are characterized by the same electrode layout (gold electroless contacts): the anode is a central electrode (2 × 2 mm2) surrounded by a guard-ring electrode, while the cathode is a planar electrode covering the detector surface (4.1 × 4.1 mm2). The results of electrical investigations point out the low leakage currents of these detectors even at high bias voltages: 38 nA/cm2 (T = 25°C) at 10000 V/cm. The time-stability and the spectroscopic response of the detectors, at different temperatures and fluxes, were investigated. 241Am spectra were measured up to 1 Mcps. The detectors were compared with the traveling heater method (THM) CZT grown detectors (Redlen), fabricated with the same electrode layout. These activities are in the framework of an Italian research project on the development of energy-resolved photon counting (ERPC) systems for high flux energy-resolved X-ray imaging.