A.W. Davies

Drift mobility and mobility-lifetime products in CdTe:Cl grown by the travelling heater method

We report the electron and hole charge transport properties of semi insulating CdTe:Cl grown by the Travelling Heater Method (THM). An alpha-particle Time of Flight (TOF) method was used to measure electron and hole drift mobility, with room temperature values of 880 cm2 /Vs for electrons and 90 cm2/Vs for holes. The variation in mobility was also investigated as a function of temperature, with electron and hole mobilities at 190 K of 1150 cm2 /Vs and 20 cm2/Vs respectively. Using a Hecht analysis the electron and hole mobility-lifetime products were also measured over the same temperature range, with values at room temperature of 8times10-4 cm2/V and 7times10-5 cm 2/V respectively. Time-resolved ion beam induced charge (IBIC) imaging was used to produce micrometer resolution maps of electron drift mobility and signal amplitude, which showed excellent spatial uniformity

Effect of dislocations on charge carrier mobility–lifetime product in synthetic single crystal diamond

The authors report correlations between variations in charge transport of electrons and holes in synthetic single crystal diamond and the presence of nitrogen impurities and dislocations. The spatial distribution of these defects was imaged using their characteristic luminescence emission and compared with maps of carrier drift length measured by ion beam induced charge imaging. The images indicate a reduction of electron and hole mobility–lifetime product due to nitrogen impurities and dislocations. Very good charge transport is achieved in selected regions where the dislocation density is minimal.

Mapping of polarization and detrapping effects in synthetic single crystal chemical vapor deposited diamond by ion beam induced charge imaging

Diamond has been regarded as a promising radiation detector material for use as a solid state ionizing chamber for decades. The parameters degrading the charge transport from what is expected from an ideal crystal are still not completely understood. Recently, synthetic chemical vapor deposited (CVD) single crystal diamond has become available, offering the opportunity to study the properties of synthesized material independent of grain boundaries. We have studied the charge transport of a synthetic single crystal diamond with α-particle induced charge transients as a function of temperature and established the presence of a shallow hole trap with an activation energy of 0.29±0.02eV in some parts of the detector. Ion beam induced charge imaging has been used to study the spatial variations of the charge transport in a synthetic single crystal diamond. Pulses influenced by the shallow hole trap had their origin close to the substrate∕CVD interface of the sample. They could be clearly distinguished from pul...

Investigation of the internal electric field distribution under in situ x-ray irradiation and under low temperature conditions by the means of the Pockels effect

The internal electric field distribution in cadmium zinc telluride (CdZnTe) x-ray and γ-ray detectors strongly affects their performance in terms of charge transport and charge collection properties. In CdZnTe detectors the electric field distribution is sensitively dependent on not only the nature of the metal contacts but also on the working conditions of the devices such as the temperature and the rate of external irradiation. Here we present direct measurements of the electric field profiles in CdZnTe detectors obtained using the Pockels electo-optic effect whilst under in situ x-ray irradiation. These data are also compared with alpha particle induced current pulses obtained by the transient current technique, and we discuss the influence of both low temperature and x-ray irradiation on the electric field evolution. Results from these studies reveal strong distortion of the electric field consistent with the build-up of space charge at temperatures below 250 K, even in the absence of external irradiation. Also, in the presence of x-ray irradiation levels a significant distortion in the electric field is observed even at room temperature which matches well the predicted theoretical model.

IBIC characterization of charge transport in CdTe:Cl

AbstractsStudies of charge transport uniformity in bulk CdTe:Cl have been carried out using ion-beam-induced charge (IBIC) imaging. High resolution maps of charge collection efficiency, mobility-lifetime product (μτ), and drift mobility (μ) were measured using a scanning microbeam of 2 MeV protons focused to a beam diameter of ∼3 μm. Excellent charge transport uniformity was observed in single crystal CdTe:Cl, with electron μτ values of up to 5 × 10−3 cm2/V s. The presence of extended defects such as tellurium inclusions was also studied using IBIC, and their influence on the charge transport performance of CdTe detector structures is discussed.

Ion Beam Induced Charge Studies of CdZnTe Grown by Modified Vertical Bridgman Method

Ion beam induced charge (IBIC) and time resolved digital IBIC techniques have been used to map the electronic properties of CdZnTe manufactured by Yinnel Tech Inc. The 2 MeV proton scanning microbeam at the University of Surrey Ion Beam Centre was used to map the charge transport properties of both holes and electrons at room temperature. The electron response of the detector showed good uniformity whereas the hole response showed significant variations across the bulk.