The goal of this paper is to review in brief the basic physics of single-election devices, as well as their-current and prospective applications. These devices based on the controllable transfer of single electrons between small conducting "islands", have already enabled several important scientific experiments. Several other applications of analog single-election devices in unique scientific instrumentation and metrology seem quite feasible. On the other hand, the prospect of silicon transistors being replaced by single-electron devices in integrated digital circuits faces tough challenges and remains uncertain. Nevertheless, even if this replacement does not happen, single electronics will continue to play an important role by shedding light on the fundamental size limitations of new electronic devices. Moreover, recent research in this field has generated some by-product ideas which may revolutionize random-access-memory and digital-data-storage technologies.

Single-electron devices and their applications

We present a comprehensive review of the material properties of cadmium zinc telluride (CZT, Cd1ˇxZnxTe) with zinc content xa 0:1‐0.2. Particular emphasis is placed on those aspects of this material related to room temperature nuclear detectors. A review of the structural properties, charge transport, and contacting issues and how these are related to detector and spectrometer performance is presented. A comprehensive literature survey and bibliography are also included. # 2001 Elsevier Science B.V. All rights reserved.

Cadmium zinc telluride and its use as a nuclear radiation detector material

Interest in superconducting microresonators has grown dramatically over the past decade. Resonator performance has improved substantially through the use of improved geometries and materials as well as a better understanding of the underlying physics. These advances have led to the adoption of superconducting microresonators in a large number of low-temperature experiments and applications. This review outlines these developments, with particular attention given to the use of superconducting microresonators as detectors.

Superconducting Microresonators: Physics and Applications

Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and /spl gamma/-ray detection. The high atomic number of the materials (Z/sub Cd/=48, Z/sub Te/=52) gives a high quantum efficiency in comparison with Si. The large bandgap energy (Eg/spl sim/1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises due to the low mobility and short lifetime of holes. Recently, significant improvements have been achieved to improve the spectral properties based on the advances in the production of crystals and in the design of electrodes. In this paper we summarize 1) advantages and disadvantages of CdTe and CdZnTe semiconductor detectors and 2) the technique for improving energy resolution and photopeak efficiencies. Applications of these imaging detectors in future hard X-ray and /spl gamma/-ray astronomy missions are briefly discussed.

Recent progress in CdTe and CdZnTe detectors

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

A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy is being developed for a space flight gamma-ray burst instrument. Two dimensional strip detectors with 100 micrometers pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 22 to 122 keV photons to less than 100 micrometers. In addition, good spectral resolution has been achieved. The uniformity of response and relative efficiency of the strip detector will be discussed. Results form electrical characterization which include strip leakage current and strip capacitance will be presented.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

CdZnTe strip detector for arcsecond imaging and spectroscopy

One of the critical challenges for large area cadmium zinc telluride (CdZnTe) detector arrays is obtaining material capable of uniform imaging and spectroscopic response. Two complementary nondestructive techniques for characterizing bulk CdZnTe have been developed to identify material with a uniform response. The first technique, infrared transmission imaging, allows for rapid visualization of bulk defects. The second technique, x-ray spectral mapping, provides a map of the material spectroscopic response when it is configured as a planar detector. The two techniques have been used to develop a correlation between bulk defect type and detector performance. The correlation allows for the use of infrared imaging to rapidly develop wafer mining maps. The mining of material free of detrimental defects has the potential to dramatically increase the yield and quality of large area CdZnTe detector arrays.

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Correlation between bulk material defects and spectroscopic response in cadmium zinc telluride detectors

The invention concerns a single detector with two designable wavelengths and bandwidths for ultraviolet detection based on n−/n+-GaN and AlGaN structures grown over sapphire substrates. The detector has several layers grown over a sapphire substrates, including a buffer layer comprising AlN; a first band-edge comprising AlX Ga1-X N; a second band-edge comprising AlYGa1-Y N; a third band-edge comprising AlZ Ga1-Z N. The detector also has ohmic contacts formed on the AlX Ga1-X N band-edge. A bias voltage is applied to the detector through the ohmic contacts so as to select a range of wavelengths in the UV region of interest.

Detector for dual band ultraviolet detection

We are developing X-ray calorimeters to meet the specifications of the Constellation-X mission. Each calorimeter consists of a transition-edge-sensor (TES) thermometer, which is suspended on a silicon-nitride membrane. Our TES thermometers are Mo/Au bilayer films that are biased in the sharp phase transition between the superconducting and normal-metal states. These calorimeters have demonstrated very good energy resolutions: 2.4 eV at 1.5 keV and 3.7 eV at 3.3 keV. The energy resolutions are limited by thermal noise and Johnson noise (which are intrinsic to any resistive calorimeter) plus excess noise. The excess noise, which is several times larger than the Johnson noise, is consistent with frequency-independent voltage noise in the TES. Detailed measurements of one Mo/Au TES demonstrate that the excess noise is independent of the voltage applied to the TES over a range of biases at the same TES resistance. The magnitude of the excess noise is smallest at the high-resistance end of the phase transition. We also compared noise in square Mo/Au TES’s ranging in size from 300 microns to 600 microns to learn how the excess noise is affected by the geometry of the TES.

Performance of Mo/Au TES microcalorimeters

Most single grains in cadmium zinc telluride (CdZnTe) grown by the high-pressure Bridgman (HPB) technique contain multiple twin boundaries. As a consequence, twin boundaries are one of the most common macroscopic material defects found in large area (400 to 700 mm2) CdZnTe specimens obtained from HPB ingots. Due to the prevalence of twin boundaries, understanding their effect on detector performance is key to the material selection process. Twin boundaries in several 2 mm thick large area specimens were first documented using infrared transmission imaging. These specimens were then fabricated into either 2mm pixel or planar detectors in order to examine the effect of the twin boundaries on detector performance. Preliminary results show that twin boundaries, which are decorated with tellurium inclusions, produce a reduction in detector efficiency and a degradation in resolution. The extent of the degradation appears to be a function of the density of tellurium inclusions.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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Carl Michael Stahle

Papers

CdZnTe strip detector for arcsecond imaging and spectroscopy

Correlation between bulk material defects and spectroscopic response in cadmium zinc telluride detectors

Detector for dual band ultraviolet detection

Performance of Mo/Au TES microcalorimeters

Effect of twin boundaries on the spectroscopic performance of CdZnTe detectors