Coplanar Grid Detectors Research Articles

Noise reduction in CdZnTe coplanar-grid detectors

Noise measurements on CdZnTe detectors show that the main sources of detector-related noise are shot noise due to bulk leakage current and 1/f noise due to the detector surfaces. The magnitude of surface leakage current appears to have little or no effect on the detector noise. Measurements on guard-ring devices fabricated using gold-evaporated contacts show that the contacts behave as Schottky barriers and that the bulk current at typical operating voltages is in most cases dependent on the contact properties rather than directly on the material's bulk resistivity. This suggests that the level of shot noise can be controlled by changing the behavior of the contacts. A significant reduction in the noise of CdZnTe coplanar-grid detectors has been obtained using a modified contact fabrication process.

Effect of differential bias on the transport of electrons in coplanar grid CdZnTe detectors

Segmented and pixilated electrode structures are used to compensate for poor hole transport in CdZnTe devices used for gamma-ray spectrometry and imaging. Efforts to model these structures have focused primarily on geometric effects; however, device performance also depends on the physical properties of the bulk and surface material, as well as the electrodes. In this paper, we describe experiments to characterize the electric field near the anode of a coplanar grid detector. The experiment is contrasted with a calculation that is based on an assumption commonly used to reduce the computational effort required to determine internal electric fields. Explanations for differences between the calculation and the experiment are proposed.

A CdZnTe coplanar-grid detector array for environmental remediation

A portable, room-temperature gamma-ray spectrometer is being developed for use in environmental remediation activities. Good energy resolution and high-detection efficiency are achieved using an array of CdZnTe coplanar-grid detectors. The array is of modular design, which allows for the stacking of an arbitrary number of detectors, as well as for the easy exchange of detectors for repairs if needed. Each element of the array consists of a 1 cm 3 detector and low-power readout electronics. Each detector module including the electronics fits within a small footprint of 1.4 cm×1.4 cm, thus allowing the detectors to be closely packed. A compliant detector-mounting scheme has been developed to protect the detectors from mechanical shock and vibration expected in field use. A prototype 2×2 array has been constructed and evaluated. The design of the detector, detector module and test results from the array are presented.

Development of high efficiency, multi-element CdZnTe detectors for portable measurement applications

We describe the development of detector arrays and electronics for large-volume, hand-held CdZnTe detectors with the same counting efficiency as portable NaI(Tl) detectors presently used for nuclear material measurement applications. The pulse-height resolution of the multi-element detectors is at least three times better than NaI(Tl) over a wide energy range (from 100 keV to several MeV), enabling more accurate measurements of gamma-rays emitted by special nuclear material. Arrays of up to eight coplanar grid detectors can be combined to make detectors ranging in size from 4 to 14 cm3. Because the number of spectroscopy channels is small, low-power, hand-held detectors can be manufactured with conventional printed circuit board technology, thus keeping the cost of multi-element detectors to a minimum. The design and performance of an 8-element detector is presented.

Weighting potentials in CdZnTe /spl gamma/-ray detectors with segmented electrodes

Weighting potentials in the metallized and non-metallized regions at the surface of CZT strip and coplanar-grid detectors an measured by scanning an /spl alpha/ source or a laser spot across the segmented face and recording the charge induced on various electrodes after the electron collection time. These measurements are found to be in good agrement with the solution of Laplace equation with mixed boundary conditions.

Coplanar-grid CdZnTe detector with three-dimensional position sensitivity

A three-dimensional position-sensitive coplanar-grid detector design for use with compound semiconductors is described. This detector design maintains the advantage of a coplanar-grid detector in which good energy resolution can be obtained from materials with poor charge transport. Position readout in two dimensions is accomplished using proximity-sensing electrodes adjacent to the electron-collecting grid electrode of the detector. Additionally, depth information is obtained by taking the ratio of the amplitudes of the collecting grid signal and the cathode signal. Experimental results from a prototype CdZnTe detector are presented.

Performance of CdZnTe detectors passivated with energetic oxygen atoms

Noise caused by surface-leakage current can degrade the performance of CdZnTe spectrometers, particularly devices with closely spaced contacts such as coplanar grid detectors. In order to reduce surface leakage, we are treating CdZnTe detector surfaces with energetic, neutral oxygen atoms. Energetic oxygen atoms react with the surface to form a resistive oxide layer. Because the reaction is effective at room temperature, deleterious heating of the substrate is avoided. In most cases, leakage current and noise are shown to decrease significantly after treatment. The effect of the treatment on the performance of coplanar grid detectors is presented.

Performance of CdZnTe coplanar-grid gamma-ray detectors

The spectral performance of coplanar grid detectors using currently available CdZnTe materials is examined theoretically and experimentally. Calculated spectral response based on the typical carrier mobility-lifetime products of current CdZnTe materials shows that energy resolution close to the charge-statistics limit can be achieved. Charge transport nonuniformity, which may limit the spectral performance of present detectors, is studied using alpha particle scanning.