Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

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Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

Hybrid perovskite crystals are integrated onto silicon wafers enabling fabrication of an X-ray linear detector array. High sensitivity may reduce patient dose in medical imaging applications.

Monolithic integration of hybrid perovskite single crystals with heterogenous substrate for highly sensitive X-ray imaging

The Shockley–Ramo theorem is reviewed based on the conservation of energy. This review shows how the energy is transferred from the bias supplies to the moving charge within a device. In addition, the discussion extends the original theorem to include cases in which a constant magnetic field is present, as well as when the device medium is heterogeneous. The rapid development of single polarity charge sensing techniques implemented in recent years on semiconductor γ-ray detectors are summarized, and a fundamental interpretation of these techniques based on the Shockley–Ramo theorem is presented.

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Review of the Shockley–Ramo theorem and its application in semiconductor gamma-ray detectors

Certain exemplary embodiments can provide a composition, system, machine, device, manufacture, circuit, and/or user interface adapted for, and/or a method and/or machine-readable medium comprising machine-implementable instructions for, activities that can comprise, after removing a cast device from a stack-lamination-derived mold, said cast device formed from a molding composition, applying a desired shape to said cast device to form a shaped cast device, said molding composition comprising: a ceramic composition comprising silica; an cycloaliphatic epoxy binder composition, said cycloaliphatic epoxy binder composition present in said molding composition in an amount up to 30% by weight of said molding composition; a silicone composition comprising a siloxane resin, said silicone composition present in said molding composition in an amount up to 30% by weight of said molding composition; and a solvent composition adapted to dissolve said cycloaliphatic epoxy binder composition and said silicone composition.

Systems, devices, and/or methods for manufacturing castings

A summary is presented of the present status of several compound semiconductor radiation detectors, including detectors fabricated from GaAs, HgI2, CdTe, Cd1−xZnxTe and PbI2

Room-temperature compound semiconductor radiation detectors

A high-energy photon imaging system including an imaging head, a signal processor, a data acquisition system and an image processing computer. The imaging head includes a detector comprising a plurality of closely-packed detection modules. Each detection module comprises a plurality of detection elements mounted to a circuit carrier. The detection elements produce electrical pulses having amplitudes indicative of the magnitude of radiation absorbed by the detection elements. The circuit carrier includes channels for conditioning and processing the signals generated by corresponding detection elements and for preparing the processed signals for further processing by a signal processor. Each conditioning and processing channel stores the amplitudes of the detection element electrical pulses exceeding a predetermined threshold. The detection modules employ a fall-through circuit which automatically finds only those detection elements that have a stored pulse amplitude exceeding the threshold. The fall-through circuit searches for the next detection element and associated channel having a valid event. The signal processor performs diagnostics, gain normalization, and response efficiency normalization functions. The data acquisition system controls the acquisition and processing of data received from the conditioning and processing channels, produces image data based upon the data in a format that is compatible with existing imaging cameras, and transmits the data to the image processing computer. The image processing computer formulates images based upon the processed signals and displays the formulated images on a display device.

Semiconductor gamma-ray camera and medical imaging system

A radiation detector for detecting ionizing radiation. The detector includes a semiconductor having at least two sides. A bias electrode is formed on one side of the semiconductor. A signal electrode is formed on a side of the semiconductor and is used to detect the energy level of the ionizing radiation. A third electrode (the control electrode) is also formed on the semiconductor. The control electrode shares charges induced by the ionizing radiation with the signal electrode, shielding the signal electrode until the charge clouds are close to the signal electrode. The control electrode also alters the electric field within the semiconductor, such that the field guides the charge clouds toward the signal electrode when the clouds closely approach the signal electrode. As a result, signal loss due to trapped charge carriers (i.e., electrons or holes) is minimized, and low-energy tailing is virtually eliminated. A fourth electrode can be added to separate the charge-shielding and field shaping functions of the control electrode. More electrodes can be added to further enhance both functions. The invention can be used in several cross-strip detector configurations, in a side-entry radiation detector, and with liquid/gas ionization detectors.

Semiconductor radiation detector with enhanced charge collection

Results of recent efforts in the growth of Cd1−xZnxTe crystals by a high pressure Bridgman (HPB) method and their use in gamma- and X-ray detector applications are presented. Evidence for crystals of relatively low defect content include etch pit densities of ≤ 104cm−2, double crystal rocking curve linewidths of 10–15″ and sharp, bright emission lines with excitonic features in low temperature photoluminescence measurements. Resistivities in excess of 1011 ohm cm are achieved without impurity doping. The resulting low leakage currents lead to good energy resolution, <6% at 59.5 keV for example. The dependence of leakage current on temperature from 233 K to 373 K implies a Fermi level at mid-gap for x=0.2. The results of flash X-ray experiments indicate that the high current sensitivity, low leakage current and good temporal response of Cd1−xZnxTe detectors make them attractive candidates for applications involving short pulses at high dose rates.

Gamma- and X-ray detectors manufactured from Cd1−xZnx Te grown by a high pressure bridgman method

This paper reports the first high spatial resolution room-temperature semiconductor gamma detector arrays. Results of wafer-scale fabrication of 48 by 48 element CdZnTe (CZT) arrays with 125 μm element pitch are presented. Performance characteristics are presented, including pulse height spectra using charge-sensitive preamplifier readout from witness test pixels, which show excellent energy resolution. High bulk and surface resistivities have been verified for these arrays, thus good energy resolution with multiplexer readout is expected.

Pixellated CdZnTe detector arrays

We report the development of a CdZnTe gamma ray imager whose advantages over the conventional Anger camera include: 1) improved contrast and spatial resolution resulting from superior energy resolution and unambiguous position determination and 2) the small size and weight and high reliability inherent in an all-solid-state construction. It provides high energy resolution and peak efficiency by incorporating Digirad's new SpectrumPlus/sup TM/ detector technology. The new imager employs a modular design, in which each 1"/spl times/1" module incorporates a monolithic 64-element CdZnTe detector array and ASIC-based circuitry that provides signal conditioning for every channel, identification of valid events and addressing functions. Imagers with a wide range of sizes and shapes can be assembled by timing modules together on a specially designed signal routing board.

Boris Apotovsky

Papers

Semiconductor gamma-ray camera and medical imaging system

Semiconductor radiation detector with enhanced charge collection

Gamma- and X-ray detectors manufactured from Cd1−xZnx Te grown by a high pressure bridgman method

Pixellated CdZnTe detector arrays

CdZnTe solid-state gamma camera