We present a brief review of results concerning the doping or compensation of CdTe by different elements like halogen, group IV, hydrogen and 3d transition elements for high resistivity materials. Comparison with theoretical models and discussion of results under this light is provided.

The performance characteristics of a linear array composed of several hundred miniature spectroscopy grade CdTe detectors are described. The linear array is utilized in a X-ray security imaging system. It operates either in an energy dispersive mode to highlight certain atomic elements in the luggage or in a regular mode for obtaining only the transmission image of the luggage. The array functions in the photon counting mode and tolerates count rates as high as 106 counts/sec. The array has high quantum efficiency and good spatial resolution which result in excellent image quality. The dynamic range, the electronic noise, the energy resolution, the homogeneity of response among detectors and the image quality are presented.

Results of a program to improve the performance of Cd1-xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cdl-xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cdl-xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-xZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.

The use of cadmium telluride (CdTe) semiconductor nuclear detectors is continuing to expand into new areas because of their unique properties which include room temperature operation and high detection efficiency. In addition, they remain the material of choice in many critical applications such as nuclear medicine and power plant monitoring because of their reputation for reliability and long term stability1. CdTe is by far the most developed of the compound semiconductors used in nuclear detector applications and it offers a number of significant benefits to researchers, clinicians and engineers who have special requirements relating to size, sensitivity and operating temperature.

Recently, there have been improvements in the growth of the crystalline material and in the fabrication procedures which have resulted in better performance and in the ability to produce arrays. This article describes the physical and electronic properties of CdTe nuclear detectors, discusses how the crystal growth and device fabrication procedures can affect these properties, and compares the performance to CdZnTe detectors.

The importance of bulk defects in Si to the performance of Si radiation detectors is discussed and the current state of knowledge about deep level defects, including those induced by radiation damage, is briefly reviewed. The importance and origins of the fluctuations in the spatial distribution of the shallow point defects which determine the uncompensated net impurity density are discussed and information on this problem in FZ silicon, multipass FZ silicon, neutron transmutation doped Si, and radiation damaged Si is presented and compared to what should be expected on the basis of simple modeling. A new model for radiation damage induced changes in the net uncompensated impurity density is reviewed and compared to experimental data on fast neutron damage in Si.

Fast neutron radiation damage in silicon results in defect levels which are predominantly acceptor-like at low fluences and may be used to compensate high resistivity ntype material to create very high effective resisitivity material. Compensated material to the order of Neff below 1011/cm3 enables depletion of diode thicknesses ≥ 1mm at reasonable biases (<100V), yielding diodes of reasonable area and capacitance<1 pF which are suitable for low noise applications such as X-ray spectrometry. Although exposure to fluences of this order will greatly increase the generation current and require cooling, most high resolution X-ray spectrometry systems are routinely operated at reduced temperature to achieve low noise operation of the front end electronics. Silicon p+ /n− /n+ implanted devices (area ≤0.25 cm2) made on high resistivity FZ silicon have been irradiated by 1 MeV neutrons to fluences of a few times 1012 n/cm2. Thick n− substrates (d=630 μm and 1000 μm) were used to achieve detector capacitances εεo/d in the range of 1 pF. After a neutron fluence of ϕn=2.9×1012 n/cm2, the total depletion of a p+/n−/n+ detector, 1040 μm thick and an area of 0.1 cm2, is reached at about V=50 Volts, with a Cd of 1 pF and a neutron induced leakage current of about 300 nA at room temperature. A total depletion of an 680 μm thick detector was reached after the fluence of 2-5×1012 n/cm2 at a voltage of 20 volts, and the capacitance of a 0.25 cm2 diode is 4.5 pF The resistivities of the compensated detector substrates are in the range of 100 K Ω-cm, and are not inverted to “p” type. The trapping of collected charge by neutron induced deep levels is modeled and simulated, and is found to be less than a few percent; with no obvious effect on peak shape. Using a resistive feedback preamplifier of modest noise contribution (225 eV), resolution of the Mn K∝ X-ray was 255 eV (FWHM) with 3 μsec shaping time constants. Other effects of uncollected charge will be discussed and comparisons between this type of detectors and Li-drift silicon detectors will be made.

The tracking of high energy, secondary products in the Superconducting Super Collider (SSC) presents challenging sensitivity and timing requirements for the scintillating fiber converters and the optical radiation detectors planned for use as signal readouts. Silicon Avalanche Photodiodes (APD) are very promising detectors which may ultimately meet these requirements.

We have designed and manufactured 1 mm2 APDs, to be operated in Geiger mode as single photon detectors for the SSC. The progress on decreasing the APD response time by platinum doping, device thinning and external avalanche quenching is reported.

Photosensitive a-Si:H p-i-n diodes, working in photovoltaic mode, have been coupled to CsI(T1) scintillators for dosimetry applications to X-ray monitoring in the energy range from 50 keV up to 15 MeV. A “mesa” approach for p-i-n diodes has been adopted both in order to better define the geometry and to obtain very low dark current. In order to optimize the geometry, a computer program has been created which simulates light generation in the scintillator, the collection by the detector and the photovoltaic current obtained as a function of exposure rate.

Measurements have been carried out in the X-rays energy ranges 50-240 keV, at 6MeV and at 15 MeV. Detectors are linear in response and shows a good sensitivity, with the capability of measuring dose rates as low as 60 mR/h.

The agreement between experimental data and simulation outputs can be considered good.

We describe the theory of operation, design, and estimated performance of an n-channel JFET designed to be operated as a detector in an X-ray spectrometer system. We estimate that a room temperature (300 K) JFET detector can be built with performance comparable to a small area, cryogenically cooled Si(Li) detector.

The effects of ionizing radiation on MOS transistors with gate oxide thickness up to 2 μm have been investigated. The major focus of workers in this area has been on the hardening techniques of technologies. On the other side, our goal is to use MOS devices to reach higher sensitivities in order to detect small amounts of dose. Therefore, sensitivity as well as temperature response in the mil-std range and stability of the dosimeters have been studied.

For the high quality Si Photodetector, the high resistivity epitaxial wafer using the low resistivity substrate were studied. The buffer layer was introduced in the interface, and it was very effective on the crystal quality of the epitaxial layer. Recombination lifetime in the epitaxial layer became very uniform and long even in the interface region which was confirmed by measuring the lifetime depth profiles. Then Si PIN Photodiode was fabricated on the above high quality epitaxial wafer and its optoelectric characteristics was evaluated.

<Directly-bonded wafers were characterized using capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. We also studied silicon on insulator (SOI) wafers with different interfacial oxide thicknesses. In the active layers of the directly bonded wafer, two dominant electron traps (Ec-0.16eV, Ec-0.24eV) were observed at 23 μμμμm from the bonded interface. Both trap densities are almost constant (about 2 × 1011cm−3) at distances larger than about 10 μm. In the substrate, the density of the shallower electron trap increases (about 8 × 1011 cm−3) within about 20 μm from the interface, while the other trap concentration is almost constant and nearly equal to that in the active layers. No trap was observed near the wafer backside. These traps were also observed in the bonded SO1 wafers. Both the trap concentrations depend on the thickness of the bonded interfacial oxide. The shallower trap concentration increases with increasing oxide thickness, and the deeper one decreases.

Charge induced as a function of time in a-Si:H p-i-n detectors by protons having energies ranging between 5 and 12 MeV have been studied. A multiple trapping transport model is developed in order to explain the non saturation of the collected charge with bias and evidence of a bias dependent recombination process is shown. The dependence of the total induced charge (the detector efficiency) with bias can be expressed by an Onsager function with a thermalization distance of 34 Å.

A silicon photodiode 10 sqmm area designed for 0,45 A/W and maximum sensitivity at 900 μm, was tested as X and gamma-ray detector in the 6-122 keV range. The simple structure, good manufacturing and passivating for a NIP photodiode (6 KΩcm,p- type material) gives a yield of 20% from batch with suitable characteristics for low energy X and gamma-ray detection. A cheap nuclear detector for technical measurements results. Evaluation and analysis of parameters in X and gamma detection is made for these silicon structures; they are mounted on TO-8 holders without entrance lenses. The applications proposed namely the composition test of alloys (with known matrix) by X-ray fluorescence analysis and in radiation safety field (absorbed dose survey), ex. in radiological clinics defectoscopic laboratories or in front of video displays.

We evaluate the electrical properties of the silicon-on-insulator (SOI) layer made by the wafer bonding using a noncontact laser beam induced conductivity/current (LBIC) method. Since the thickness of the SOl layer used in this study is about 40μm, the He-Ne laser, whose penetration depth for Si is small (about 3μm), is used as the carrier-injection light source.

We use the SOI wafer with some voids which are revealed by the X-ray topography. We have reported that the LBIC signal intensity decreases in the void region. In this study, we measure the microscopic signal variation near the edge of the void. It is observed that the LBIC signal intensity decreases in the outside region within a distance of about 700μm from the void edge. The diffusion length of the injected carrier (100-150μm) is shorter than the width of the region where the signal intensity decreases. Thus the decrease is not due to the carrier diffusion to the void. These results show that the formation of the void degrades the electrical properties not only in the void region but also outside the void.

The optical constants n and k are determined for p-type silicon at the Eo and El and critical point energies for one MeV electron irradiated samples. The value for fluences of 1014 and 1016 e−/cm2 are compared to samples before irradiation. The real, ε1 and imaginary,ε2 components of the dielectric function, ε, used to find n and k, were obtained by measurement of tanψ and δ using spectroscopic ellipsometry (SE). The data show that changes in δ, in particular, are greater in the region about Eo than of E1. This is consistent with electrolyte electroreflectance (EER) results in which the Lorentz line shape is narrower for Eo than for E1. The value of n is found to increase and k to decrease with e- radiation at the critical points, although, neither does so monotonically. The change in n at the Eo critical point is greater than at the higher energy main structure E1 whereas, k is a slower varying function in this region.

The design and performances of a system for high resolution X-ray spectroscopy are presented. The detector is a low capacitance diode built on high resistivity silicon. The signal preamplification is made by means of an ultra-low noise charge amplifier of new conception. Presently the system exhibits an equivalent noise charge of 61 r.m.s. electrons at 297 K and 32 r.m.s. electrons at 223 K. It is shown how an improvement down to 30 r.m.s. electrons at room temperature is expected employing an integrated transistor on the detector chip.