Diamond is a resilient material with rather extreme electronic properties. As such it is an interesting candidate for the fabrication of high performance solid state particle detectors. However, the commercially accessible form of diamond, grown by chemical vapour deposition (CVD) methods, is polycrystalline in nature and often displays rather poor electrical characteristics. This paper considers ways in which this material may be used to form alpha particle detectors with useful performance levels. One approach adopted has been to reduce the impurity levels within the feed-stock gases that are used to grow the diamond films. This has enabled significant improvements to be achieved in the mean carrier drift distance within the films leading to alpha detectors with up to 40% collection efficiencies. An alternative approach explored is the use of planar device geometries whereby charge collection is limited to the top surface of the diamond which comprises higher quality material than the bulk of the film. This has lead to collection efficiencies of 70%, the highest yet reported for polycrystalline CVD diamond based detectors. Techniques for improving the characteristics of these devices further are discussed.

Semi-insulating liquid encapsulated Czochralski grown GaAs has been investigated after irradiation at high fluences of high-energy protons. Electron beam induced current observations of scanning electron microscopy evidenced a radiation stimulated ordering. An analysis has been carried out of the deep levels associated with defects as a function of the irradiation fluence, using complementary current transient spectroscopies. By increasing the irradiation fluence, the concentration of the native traps at 0.37 eV together with that of the EL2 defect significantly increases and, at the same time, two new electron traps at 0.15 eV and 0.18 eV arise and quickly increase in density.

We develop a Monte Carlo simulator of the charge signal induced by an external radiation on a semi-insulating GaAs detector. The role played by trapping and detrapping processes and the dynamics of generated carriers are investigated. The relative contribution to the charge signal of fast and slow time components as well as the time constant of the slow component are studied as a function of the applied voltage. Present findings provide a physical interpretation of available experimental results.

Large area transmission and section topographs of semi-insulating gallium arsenide wafers grown by the gradient freeze technique are made with synchrotron radiation at HASYLAB in Hamburg and at ESRF in Grenoble. Several high-resolution images including stereo pairs are obtained on the same film at a time. A typical dislocation line is an arc of a circle which starts from one surface and ends at the same surface. From the disappearance of the dislocation image and using the g · b = 0 criterion it is concluded that the Burgers vector b of the most common dislocations is parallel to 〈110〉. Rather large volumes of the wafer are dislocation-free. Section topographs of epitaxial wafers show defects and strain fields at the interface between an n-type substrate and the epitaxial layers grown by chemical vapor deposition. The results are compared with those obtained from detector performance measurements.

We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy (LPE) and the fabrication of room temperature p-i-n radiation detectors. Our epilayers are grown from a Ga solvent in a graphite boat in a pure hydrogen atmosphere. Growth is started at a temperature of approximately 800 °C. Our best epilayers show a net-residual-donor concentration of 2×1013 cm−3, confirmed by Hall effect measurements. The residual donors have been analyzed by far infrared spectroscopy and found to be sulfur and silicon. Epilayers with thicknesses of up to 120 µm have been deposited on 650 µm thick semi-insulating GaAs substrates and on 500 µm thick n+-type GaAs substrates. We report the results obtained with Schottky barrier diodes fabricated from these high purity n-type GaAs epilayers and operated as X-ray detectors. The Schottky barrier contacts consisted of evaporated circular gold contacts on epilayers on n+ substrates. The ohmic contacts were formed by evaporated and alloyed Ni-Ge-Au films on the back of the substrate. Several of our diodes exhibit currents of the order of 1 to 10 nA at reverse biases depleting approximately 50 µm of the epilayer. This very encouraging result, demonstrating the possibility for fabricating GaAs p-i-n diodes with depletion layers in high purity GaAs instead of semi-insulating GaAs, is supported by similar results obtained by several other groups. The consequences of using high purity instead of semi-insulating GaAs will be much reduced charge carrier trapping. Diode electrical characteristics and detector performance results using 55Fe and 241Am radiation will be discussed.

Results are presented of a study on the performance degradation and the induced lattice defects of In0.53Ga0.47As p-i-n photodiodes, subjected to 220-MeV carbon particles. The effects on both the dark current and the photo-current are investigated as a function of the carbon fluence and correlated with DLTS results. The device degradation is compared with the one observed after exposure to 1-MeV electrons, 1-MeV fast neutrons and 20-MeV alpha rays, respectively. The differences in damage coefficients will be explained in view of the calculated number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the diode performance and of the induced deep levels by isochronal annealing is also reported.

A study of electrical properties and detection performances of the semi-insulating (SI) InP based detectors is presented. Detectors with a top P+ layer and a Schottky back contact give the charge collection efficiency about 90 % and an energy resolution 3.7% (FWHM) for 5.48MeV α-particles at 250 K. Detection of X-rays (122 keV and 60 keV) photons in temperature region 220–250 K is demonstrated. Multiple peaking observed during detection of photons is discussed.

High quality ZnS epilayers were grown on GaAs and GaP substrates by hot wall epitaxy. The optimum temperature conditions for high quality ZnS epilayer were found. The photoluminescence(PL) spectrum of high quality ZnS epilayers showed sharp and narrow exciton peaks and no self-activated peaks. The room temperature energy gap of ZnS/GaAs was found to be 3.729 eV from the experimentally observed free exciton PL peaks. The temperature dependence of the PL intensity showed a two step quenching process and the temperature dependence of the PL linewidth broadening was tried to analyze in terms of exciton scattering process. From the splitting of the heavy hole and the light hole exciton peaks, the strain was identified.

ZnSe annealed in (Zn + 46 wt.% TI) vapors and in Zn melt with 5 wt.% TI addition was investigated. The radiation spectra in the regimes of stationary and pulsed photoluminescence (PL) with the time delaying at 77K were studied. By using coloured cathodoluminescence (CCL) combined with the crystal cleavage image in the secondary electrons reflection the impurities and defects volume distribution was evaluated. It was revealed that at the annealing of ZnSe crystals in TI vapors, the cleavage surface has light blue radiation on the red background with an homogeneous field distribution with the dimensions ˜ 1..10μm. On the edge of the cleavage on the depth of 10μm the region of yellow radiation is observed. At the annealing in the melt the irradiation became blue on a weak red background, the homogeneity enhances. At the room temperature PL spectra correspond with images of cleavage in CCL. In the PL (at 77K) spectra in the exciton region there were observed: bands at 445nm (blue radiation); edge radiation at 460nm, 485nm with the LO phonons replica (blue region) and in the impurity region: bands 500...570nm (yellow-green radiation); 600...700nm and 720...800nm (red radiation). The investigation of PL of the annealed samples surface allowed the suppose, that the bands at 2,76eV (450nm), are stipulated by the free-bound transition on the acceptor center (E + 40meV), including TI.

The comparison of ion and tetrahedronical covalent radiuses of Zn, Se and TI, electronegativity, probability of Zni and Vse. formation at the annealing allowed to suppose that, TI fills Vse. and forms (Zni Tls) and (Vse. Tlse) complexes. The carried out theoretical calculations according to the model of two-atom molecule gives the energy of complexes occurrence (Ev + 0,04) eV and (Ev + 0,8) eV. The first value accordingly is in good agreement with the experimental data.

We have characterized ZnSe material grown by chemical vapor transport in iodine using triple-axis X-ray diffraction (TAD), photo-induced current transient spectroscopy (PICTS), photoluminescence (PL), current-voltage measurements and gamma-ray spectroscopy. The material was found to have inadequate carrier transport for nuclear spectrometer use, but there was a discernible difference in performance between crystals which could be correlated with crystallinity as determined by the TAD rocking curves.

Time-resolved photoluminescence (TRPL) at T=4,2K, electron paramagnetic resonance (EPR) in the range of 4,2K–77K, and wavelength modulated transmittance (WMT) spectra for both undoped and annealed in Bi and Zn melts ZnSe single crystals have been investigated. It is found that the annealing in Bi melts leads to recovery of crystal structure. This supposition is based on the increase of fine and hype fine interaction of residual Mn2+, ions with the simultaneous decrease of the EPR signals line width and the decrease of the F-center line. Furthermore, the band with λmax=520 nm disappears, while exciton band I1 (λmax=445 nm) and edge band Q0 – DAP (λmax=460,2 nm), involving AlZn – LiZn, pairs, become more revealed. At the same time, band narrowing of the TRPL spectra was observed. The annealing in Zn melt causes the increase of the number of F-center. From WMT spectra the energy position of local centers and the dominant influence on impurities and defects of the crystal structure were investigated.

Single crystals of ZnSe, with varying amounts of Cr doping have been studied using Raman and photoluminescence(PL) spectroscopy. The Cr-doped samples show the existence of a coupling mechanism of longitudinal optical(LO) phonons of ZnSe with hole-plasmons. The dependence of intensity ratio of LO and transverse optical(TO) mode on temperature and excitation wavelength, has been attributed to the interaction of the field of LO phonons with the surface electric field in the depletion layer. The interaction of discreet phonons with the electronic continuum of conduction band in ZnSe is responsible for the shift of Raman peaks. The large electron capture cross-section of deep-level Cr2+ and Cr1+ impurities is inhibitive for the observation of band-to-band PL transition at ˜2.7eV in ZnSe:Cr.

ZnSe, although generally thought of as a wide band gap semiconductor, is insulating in the as-grown state. It is only after heat treatment in a zinc rich atmosphere that semiconducting properties are observed Therefore, dielectric spectroscopy is an appropriate tool to study the electrical properties of as grown ZnSe. The dielectric properties of large-grained samples of ZnSe grown by physical vapor transport were measured as a function of frequency. Differences can be seen in the dielectric properties of samples grown under different conditions (such as the effect of a seed and the orientation of the gravity field during growth). The spectra of heat treated samples were also acquired and were found to exhibit significant deviations from those of the as grown crystals.

Low temperature (LT) processed ZnSe MSM photodetectors can be used for detecting Gamma rays or X-rays using scintillation crystals in many space and medical applications. Metalsemiconductor-metal (MSM) photodetectors were fabricated on undoped ZnSe grown by molecular beam epitaxy (MBE) on semi-insulating (100) GaAs substrates. The MSM photodetectors consist of interdigitated metal fingers with 2 μm, 3 μm, and 4 μm spacing on one chip. Probimide and SiO2 thin films were deposited to aid the LT lift-off process before the pattern generation. An interdigitated structure was achieved by photolithography and reactive ion etching. Pd Schottky metal was deposited at a substrate temperature near 77 K using a lift-off technique. The LT metallization provides an improved interface between metal and semiconductor interface. Continuous wave signal to noise ratio (SNR) of 1.57×104 was obtained for 2 μm interdigitated photodetectors, operated under 180 nW optical power at a wavelength of 400 nm. The detectors showed good DC saturation characteristics indicating a low surface recombination. Saturation current without illumination remained at around less than 1 pA for a ± 10 V biasing. Detectors exhibited linearity with light intensity and DC bias voltage suggesting no gain mechanism involved, and showed a high spectral responsivity (0.6 (A/W)) at a wavelength of 450 nm at 5V applied bias.

In this paper we examine a recently proposed concept for obtaining sub-pixel spatial resolution in compound semiconductors where hole transport properties are relatively poor. [1] This approach uses weighted sums and differences of local pixel signals to extract both accurate x-ray energy estimates and interpolate location at the sub-pixel level. A simple analysis, including noise estimates, suggests the possibility of obtaining locations at the 50–100 micron level using 1–2 mm wide stripe electrodes while obtaining 1–2% energy resolution for x-rays up to 100 keV. Following this examination, we will present the most recent experimental results from our program to develop electronics to implement this scheme.

The pulse height spectra from a new kind of unipolar gamma-ray detectors were predicted using a new three-dimensional simulation program developed at Sandia National Laboratories. The detectors were fabricated at Sandia and RMD Inc., and tested at Sandia. They were fabricated from Cd1-x.ZnxTe crystals and they were electron-transport-only devices. For the simulation, a successive overrelaxation method was used to determine the three-dimensional internal electric field within a detector, and to find the weighting potentials for the anode and the cathode. Uniform irradiation and ionization from a 137Cs source was assumed, and the charge transport and the signal induction within the detector were numerically computed using the appropriate materials and design parameters. The simulation gave excellent agreement with experimental pulse height spectra, and it demonstrated the power of such a simulation to correlate the materials parameters and the device design to the actual detector performance.

The evaluations of the following performances of detectors for design of the radiographic system were carried out by mathematical simulation method and experimentally: sensitivity to absorbed energy, noise level, form of apparatus function for spatial resolution of detectors array.

The results of calculations were used for designing of CdWO4-Si arrays with optimal sizes of scintillator and photodiode for resolution ability. At the given stage the quality of radiation detectors was evaluated by spectroscopic methods. At the bias voltage on photodiode 24 V, the sensitivity of detectors has made up (0,95–1,00) × 10−21 C / eV, noise level - (1,50–1,75) ×10−16 C together with electronic noise. Dynamic range at absorbed energy by separate detector is more than 105, what is sufficient to get required image contrast.

New applications of avalanche photodiodes as fast timing detectors for electrons ranging from 10 keV to 300 keV together with an analysis of the response of silicon avalanche photodiodes to the electrons are reported.

The XIA DXP-4C is a 4 channel, CAMAC based, x-ray spectrometer which digitally processes directly digitized preamplifier signals. The DXP-4C was designed for instrumenting multi-detector arrays for synchrotron radiation applications, and optimized for very high count rates at a low cost per detector channel. This produced a very compact and low power (3.4 W/channel) instrument for its count rate and MCA capabilities, which thus provides a strong basis for portable applications. Because all functions are digitally controlled, it can be readily adapted to various user interfaces, including remote access interfaces. Here we describe the design and examine approaches to lowering its power to 50 mW/channel. We then consider the issues in applying it to three typical portable or remote spectrometry applications.

The use of some specific compound semiconductors in the fabrication of high energy X-ray detectors shows significant potential for X-ray astrophysics space missions. We are currently investigating three high purity crystals - CdZnTe, GaAs and TlBr - as the basis for future hard X-ray detectors (above 10 keV). In this paper we present the first results on CdZnTe and GaAs based detectors and evaluate the factors currently still constraining the performance.

Energy resolutions (FWHM) of 0.9 keV and 1.1 keV at 14 keV and 60 keV, respectively, have been obtained with an epitaxial GaAs detector, while 0.7 keV and 1.5 keV FWHM were measured at the same energies with a CdZnTe detector. Based on these results it is clear, that the next generation of X-ray astrophysics missions now in the planning phase may well consider extending the photon energy range up to ∼100 keV by use of efficient detectors with reasonable spectroscopic capabilities.