CdTe Array Research Articles

Performance Assessment of Four Different Photovoltaic Technologies in Poland

Due to the observed increase of photovoltaic installations capacity in Poland, the research on the performance of different modules became an important issue from the practical and scientific point of view. This paper is intended to help system planners to choose photovoltaic modules and inverters taking into account the actual operating conditions. The study is devoted to the assessment of four different technologies of photovoltaic modules: polycrystalline silicon (pc-Si), amorphous silicon (a-Si), copper indium gallium selenide (CIGS), and cadmium telluride (CdTe). The data was collected at a solar plant located at high latitude location, in the eastern part of Poland, during the fourth year of the plant operation. The influence of irradiance on the temperature and efficiency of modules was studied. The results show that the efficiency of the pc-Si and CIGS modules decreases with rising temperature; however, the efficiency of the a-Si and CdTe modules is more stable. The impact of changing external conditions on the inverter efficiency as well as array and system losses during various seasons of the year was shown. The inverter efficiency reaches up to 98% in summer and drops as low as 30% in winter. Small average array capture losses of 7.41 (kWh/kWp)/month (0.25 h/day) are observed for the CIGS and 10.4 (kWh/kWp)/month (0.35 h/day) for pc-Si modules. The a-Si and CdTe array losses are higher, up to 2.83 h/day for CdTe in summer. The results indicate high annual energy yields of the pc-Si and CIGS modules, 1130 kWh/kWp and 1140 kWh/kWp, respectively. This research provided new data on pc-Si and especially the performance of the thin film modules and losses in a photovoltaic installation under temperate climate.

Enhanced K-Edge Radiography Using a High-Spatial-Resolution Cadmium Telluride Array Detector

To confirm the imaging effect of a dual-energy (DE) cadmium telluride (CdTe) array detector (XCounter, Actaeon) and to perform fundamental studies on DE computed tomography, we performed enhanced K-edge radiography using iodine (I) and gadolinium (Gd) media. DE radiography was performed using an X-ray generator with a 0.1-mm-diam-focus tube and a 0.5-mm-thick beryllium window, a 1.0-mm-thick aluminum filter for absorbing extremely low-energy photons, and the CdTe array detector with pixel dimensions of 0.1 × 0.1 mm2. Each pixel has a charge-sensitive amplifier and a dual-energy counter, and the event pulses from the amplifier are sent to the counter to determine two threshold energies. The tube current was a maximum value of 0.50 mA, and the tube voltages for I- and Gd-K-edge radiograms were 60 and 80 kV, respectively. In the I-K-edge radiography of a dog-heart phantom at an energy range of 33 - 60 keV, the muscle density increased, and fine coronary arteries were visible. Utilizing Gd-K-edge radiography of a rabbit head phantom at an energy range of 50 - 80 keV, the muscle density increased, and fine blood vessels in the nose were observed at high contrasts. Using the DE array detector, we confirmed the image-contrast variations with changes in the threshold energy.

Seasonal performance comparison of three grid connected photovoltaic systems based on different technologies operating under the same conditions

Three grid connected photovoltaic systems based on different PV technologies (poly-Si, a-Si and CdTe), operating under the same conditions were analysed to determine their degradation and the variation in seasonal performance. In addition to the intrinsically different degradation of each technology through indoor tests at standard test condition (STC), a deeper analysis of the variables affecting the fluctuations of the performance was performed. The performance seasonal fluctuations resulting from the solar spectrum and module temperature was studied during a single year (December 2014 to December 2015). A notable solar air mass spectrum dependence (−11.22%/AM) of the generated power but scarcely detectable instantaneous temperature dependence was observed in the a-Si array. In contrast, the poly-Si array suffered the highest power decline with an elevating temperature (−0.56%/°C). The CdTe array exhibited a tempered interaction with the solar spectrum (−4%/AM) and temperature (−0.25%/°C). Finally, the significant maximum power difference between two months (April and September) due to the thermal annealing and light soaking effects in the a-Si array is confirmed, where the quantified variation of these two effects were 5.9% and −5.7%, respectively.

3D Non-Destructive Fluorescent X-Ray Computed Tomography With a CdTe Array

In this study, we develop 2D and 3D tomographic non-destructive tests for detecting fluorescence X-rays using a 2D CdTe array. Experiments were conducted using various phantoms and image-reconstruction methods. In general, conventional computed tomography analyzes materials according to attenuation coefficients and is highly dependent on the densities of the materials; thus, it is difficult to discriminate materials that have similar densities, even if their atomic numbers differ. In our research, materials were exposed to X-rays, and both conventional transmission images and fluorescent X-ray images were reconstructed using the information from characteristic X-rays detected using a 2D CdTe planar detector array. Since atoms have their own characteristic X-ray energies, our system was able to discriminate materials of the same or similar density if the materials had different atomic numbers. Additionally, the transmission and characteristic X-ray images were combined to analyze the positions, densities, and atomic numbers of the unknown materials. Several image-reconstruction methods were applied; the reconstructed images were compared to determine an optimized algorithm for fluorescence X-ray computed tomography.

Design and fabrication of endoscope-type Compton camera

We are constructing an endoscope coupled with a Compton camera to intra-operatively inspect early stage cancer and metastatic lymph node (5mm–10mm). The radiation imaging system is composed of pixelated semiconductor detectors, which are Si array and CdTe array, whose sizes are less than 10mm×10mm, and a digital signal-processing unit with ASIC and FPGA and reconstruction algorithm using spherical harmonics that can compute in real time. In this paper, we show some simulation results on the performance of the proposed prototype detector using EGS5, Monte Carlo simulation code. The FWHM of 1mm spatial resolution for an object located 10mm away from the detector surface and the intrinsic efficiency of 0.05% were observed. Imaging and data acquisition time to take fine images are just 1min. It therefore can be considered that the endoscopic Compton camera is useful for intra-operative inspection.

The effects of photon flux on energy spectra and imaging characteristics in a photon-counting x-ray detector

The purpose of this paper was to investigate the effect of photon flux on the recorded energy spectrum and images produced with a photon-counting detector. We used a photon-counting cadmium telluride (CdTe) x-ray detector (model PID350, Oy Ajat, Finland). The CdTe array was composed of 16 384 pixels, each 0.35 × 0.35 × 0.75 mm3 in dimension. The photon flux is controlled by an additional aluminum filter (1, 10, 20, 30 and 40 mm). Images were acquired at three different tube voltages (50, 70 and 90 kVp) with various thicknesses of photon flux control (PFC) filters. The data acquisition time was changed to acquire an approximately equal number of counts within the selected energy window between different thicknesses of PFC filters at the same tube voltage. A phantom was manufactured to evaluate the photon flux effect on the image. The phantom was made from polymethyl methacrylate and four concentrations of iodine. The photon flux effect on the image was evaluated by the signal-difference-to-noise ratio (SDNR) between iodine and the background material. The changes of photon flux affected the recorded energy spectra and image. The thickness of the PFC filter that showed the maximum SDNR differed according to the tube voltage. The 10 mm PFC filter showed the highest SDNR at 50 and 70 kVp, while the 30 mm PFC filter exhibited the highest SDNR at 90 kVp. The SDNR was improved up to, on average, 30-fold in optimal photon flux conditions which acquired a spectrum including the lowest electronic noise with no pulse pile-up effect. The results of this study showed that the photon flux affected not only the acquired energy spectrum but also the image. Based on these results, the spectral distortion correction should be considered in connection with the image that is the ultimate purpose of medical imaging.

Electrodeposition of a novel CdTe array on Ni foils and photoelectrochemical performance

A novel perpendicularly aligned CdTe array with cauliflower-like morphology was fabricated on a Ni substrate using a simple electrochemical synthesis method. The samples were characterized by XRD, EDX and FESEM, and the results demonstrate that a high-purity, uniform cauliflower-like CdTe array was obtained. Rod lengths can reach to 3.0 μm, with nanoparticles stacking along the rod growth direction, keeping the diameter at 1.5 μm. A schematic diagram of the possible growth process and evolution from CdTe seed nuclei to the cauliflower-like CdTe array was proposed. The device based on the aligned array-on-Ni configuration demonstrates excellent photoelectrical properties, which is ascribed to the large absorption coefficient of the material and also suggests good electronic structure quality of the cauliflower-like rods. The technique described is applicable to fabricate highly aligned cauliflower-like semiconductor arrays on other conductive substrates.

Preliminary report on the development of a high resolution PET camera using semiconductor detectors

We are developing a PET camera using small semiconductor detectors, whose resolution is equivalent to the physical limit of spatial resolution. First, a coincidence system of 16 Schottky CdTe detectors of 0.5mm width obtained a resolution of <1mm and it was confirmed that the Schottky CdTe detector is suitable for high resolution PET. Next, the performance of a pair of 32 channel CdTe arrays (1.2mm width per channel) was investigated for the development of the prototype of high resolution PET. The time resolution between opposing detector pair was 13ns (FWHM) when high voltage (700V) was applied. The image of a 0.6mm diameter point source was obtained in an experiment with opposing detector arrays using four channels, indicating that, a higher resolution can be achieved with the 32 channel CdTe array.

Dual-energy X-ray CT with CdTe array and its extension

We have developed dual-energy X-ray CT (DXCT) using monochromatic X-ray beams. From the DXCT, we can obtain distributions of an electron density and an effective atomic number in a human body. Especially, the electron density is very important for the heavy-ion radiotherapy. Now, we adopted the CdTe array to this detector system to know the energy of incident photons as well as detect the position and the number of photons. We carry out the experiment of the DXCT with CdTe array at the beamline of KEK. The preliminary result of the experiments and the feasibility of a quantitative polychromatic X-ray CT as an advanced method of this method are shown in this study.

Hard X- and soft gamma-ray polarimetry with CdTe array prototypes

Up to date there have been very few developments in the field of polarimetry in hard X- and soft /spl gamma/-ray astronomy, even if this measurement can give unique information about the geometry and the processes responsible of high energy emission from cosmic sources. We have recently proposed an instrument devoted to polarimetric measurements in this energy range known as the Coded Imager and Polarimeter for High Energy Radiation (CIPHER), a telescope which uses a detection plane optimized for the detection of Compton scattered events. In order to study the response of this polarimeter concept to linearly polarized radiation in the 100 keV to 1 MeV energy range, we have prepared an experiment (POLCA: POLarimetry with CdTe Arrays) based on CdTe detector prototypes of 4/spl times/4 pixels. The use of a beamline at the European Synchrotron Radiation Facility (ERSF) allowed us to study the Compton double-event efficiency and distribution, for beams of nearly 100% linearly polarized radiation in the energy range from 100 keV to 400 keV. We have obtained polarimetric modulation factors higher than 0.4 with double-event efficiencies higher than 20%. The photon beam energy and detector thickness dependencies will be discussed, comparing these experimental results with those calculated using Monte Carlo simulations.

Low power BiCMOS ASIC for wide energy range X–γ ray imaging and spectroscopic detectors

A low-power, low noise Application Specific Integrated Circuit (ASIC), designed to read out CdTe array detectors for X–γ ray imaging and spectroscopy on satellite or balloon telescopes, is presented. The chip ELBA has been realized in 0.8 μm BiCMOS technology; the front-end includes preamplifier, shaper, peak stretcher, discriminator with a dynamic range from 20 keV to 2 MeV of photon energy. The reset of the preamplifier and the high time constant of the shaper are obtained with a very compact current conveyor feedback. A multichannel prototype has been realized with a digital back-end including multiplexer, decoder, double pulse detect and logic circuitry for chip testing and calibration. The measured noise level is in between 150 and 500 electrons r.m.s. corresponding to 1.5–5 keV FWHM in CdTe detectors. The total non-linearity is below ±1.5% and the cross-talk between two neighboring channels is about 0.7%. The circuit is powered with a single supply at +4 V with a total power consumption of 1 mW/channel.

A study of prototype CdTe hard X- and γ-ray detectors

CdTe array detectors are being investigated for use in a variety of applications, ranging from medical diagnosis to high-energy astronomy. Herein, we present a study of the spatial resolution of several prototype CdTe arrays of varying thickness as a function of energy and angle of the incident radiation. These measurements were performed at the European Synchrotron Research Facility at Grenoble, France in the first week of July 2002. The energy range employed was between 100 and 500 keV, while the detectors consisted of a set of CdTe arrays containing elements of thicknesses between 3 and 8 mm. The spatial response of the detectors was measured using single site events, while the possibility of using this type of array detector also for measuring the degree of polarisation of the radiation was investigated using multi-site interactions.

Recent development of radiation measurement instrument for industrial and medical applications

Recently, computer imaging technology has developed very high-quality image and fast processing time. X-rays have been used for many purposes such as medical diagnosis and analyzing the structure of industrial materials. However, as X-rays are hazardous to the human body, it is desirable to reduce its exposed dose to a minimum. For this purpose, it is necessary to use a semiconductor radiation detector with a high efficiency for X-rays. We have developed photon-counting CdTe array detector system for medical and industrial use. The bone densitometer for Dual Energy X-ray Absorptometry (DEXA) has been developed to make diagnosis of osteoporosis, and it is developed to analyze a material element for industrial use. Recently, we have developed a monochromatic X-ray CT using a 256 ch CdTe array detector. We found that the array detector systems are very useful for medical and industrial applications.

CIPHER: coded imager and polarimeter for high-energy radiation

The CIPHER instrument is a hard X- and soft γ-ray spectroscopic and polarimetric coded mask imager based on an array of cadmium telluride micro-spectrometers. The position-sensitive detector (PSD) will be arranged in 4 modules of 32×32 crystals, each of 2×2 mm 2 cross section and 10 mm thickness giving a total active area of about 160 cm 2. The micro-spectrometer characteristics allow a wide operating range from ∼10 keV to 1 MeV, while the PSD is actively shielded by CsI crystals on the bottom in order to reduce background. The mask, based on a modified uniformly redundant array (MURA) pattern, is four times the area of the PSD and is situated at about 100 cm from the CdTe array top surface. The CIPHER instrument is proposed for a balloon experiment, both in order to assess the performance of such an instrumental concept for a small/medium-size satellite survey mission and to perform an innovative measurement of the Crab polarisation level. The CIPHER’s field of view allows the instrument to keep a single source within the field of view for a long observation period without requiring a precise pointing system. Herein we describe the instrument design, together with results obtained in our development studies, in particular on CdTe micro-spectrometers and the integrated front-end electronics. Furthermore, we present the expected operational performance in terms of image and spectral quality (angular and energy resolution) and polarimetric capabilities for an observation of the Crab nebula from balloon altitudes.

CMOS low-noise switched charge sensitive preamplifier for CdTe and CdZnTe X-ray detectors

CdTe and CdZnTe X-ray detector arrays for imaging and spectroscopy provide low capacitance current sources with low leakage currents. The optimal shaping time for low-noise operation is relatively high in CMOS analog channels that provide the readout for these detectors. The shaper is centered at lower frequencies, and thus the 1/f noise from the electronics is the main noise source that limits the resolution of the channel. The optimal dimensions of the input stage MOSFET are determined by this noise. In this paper a design criterion for the optimization of the resolution and the power consumption in a 1/f noise dominated readout is introduced. A readout based on CMOS switched charge sensitive preamplifier without feedback resistor has been designed and fabricated in the CMOS 2-/spl mu/ low-noise analog process provided by MOSIS. This design provides high sensitivity and the possibility to integrate a large number of channels with low power consumption. Measurements of the performance of a first prototype chip are presented.

A 90 element CdTe array detector

The fabrication of a CdTe array radiation detector and its radiation detection characteristics are described. In order to obtain high efficiency of charge collection and realize uniform detection sensitivity, current-voltage characteristics with the combination of large and small barrier height contacts and three kinds of CdTe crystals have been investigated. It was found that the Schottky barrier height of electroless Pt deposition was 0.97 eV, which effectively suppressed electron injection. By using the crystal grown by the travelling heater method with a Cl concentration of 2 ppm, carrier lifetimes for electrons and holes of 1.0 and 0.5 μs, respectively, were achieved. A 90 element array detector exhibited an energy resolution as low as 4.5 keV and a count rate variation of less than 5% for 60 keV γ-rays.

Performance of S-192 (Hg,Cd)Te Arrays

Very high performance (Hg,Cd)Te photoconductive detectors have been fabricated for use on the S-192 experiment, which is a multispectral scanner being built by Honeywell for the NASA Manned Space Center's Skylab. The S-192 will scan the earth from Skylab and record data in twelve near ir spectral bands and one long wavelength band. The near ir bands range from 0.4 micro to 2.35 micro. At 87 K with a 90 degrees FOV, we have consistently produced arrays with specific detectivities at 2.35 micro close to or greater than 8 x 10(11) cm Hz((1/2))/W and with detective time constants less than 1 microsec. These detectors demonstrate good uniformity in performance across an array. State-of-the-art fabrication techniques have been used to make detectors with good definition that are 5-10 micro thick with 25-micro spacing between elements.