Compound Semiconductor Detectors Research Articles

An energy-resolving photon-counting X-ray detector for computed tomography combining silicon-photomultiplier arrays and scintillation crystals.

X-ray photon-counting computed tomography (PCCT) has garnered considerable interest owing to its low-dose administration, high-quality imaging, and material decomposition characteristics. Current commercial PCCT systems employ compound semiconductor photon-counting X-ray detectors, which offer good energy resolution. However, the choice of materials is limited, and cadmium telluride or cadmium zinc telluride is mostly used. Although indirect radiation detectors can be used as alternatives to compound semiconductor detectors, implementing fine-pitch segmentation in such detectors is challenging. Here we designed an indirect fine-pitch X-ray photon-counting detector by combining miniaturized silicon photomultiplier arrays and fast scintillation crystals, with a pixel size of 250 µm, for future indirect PCCT. The fabricated array detector has the potential to discriminate photon energies with a 27% resolution at 122 keV, 296 µm spatial resolution, and charge-sharing inhibition ability.

Cadmium Telluride (CdTe) Compound and Silicon (Si) Semiconductor Materials Detectors for X-Ray

There are different approaches and also materials to construct a detector for x-rays. the available semiconductor materials, Silicon (Si) is mainly used for charged particle detectors and soft X-ray detectors. Cadmium Telluride (CdTe) compound semiconductors for x-ray detectors have experienced a rather rapid development in the last few years, due to their appealing performance. In this paper we review the physical properties of semiconductor detectors for x-ray. In particular, we focus on compound semiconductor detectors. In addition, Si detector has better energy resolution achievement. However, it does not have good detection efficiency for higher energy above (40Kev). While CdTe detector supplies higher detection efficiency for x -rays about 100% for up to 100 keV in energy. The response functions of Si detector to reduce small x-ray, which has limited sensitivity for energy about 30keV. The XR-100T is high performance for x-ray and gamma ray detector by using 241Am (59.5keV), so the cooler are mounted the input FET a feedback components to the Amptek to charge sensitive preamplifier. Both the Si and CdTe detectors are connected to the PX2 combined amplifier and power supply, that was provide the voltage needed to operate XR-100T CdTe. The PX2 T CdTe amplifier has a Rise Time Discrimination circuit, measure the FWHM energy resolution of 55Fe (5.89) the peak in each spectrum hence a graph of energy resolution. Moreover, the Rise Time Discrimination So the escape peak of 55Fe was determined with Si detector was 11.66 keV, also k- sell x-ray energy was calculated to 5.77keV and the Rise Time Discrimination effect was studied on the spectrum when is it switched on and off. Its influence was found in decreasing the noise of the spectrum.

Response of Cadmium Zinc Telluride Compound Semi-Conductor Detector against Gamma Photons by Efficiency Calculation: A Microdosimetry Simulation Study

Introduction: Cadmium zinc telluride has recently been used as a compound semiconductor detector in a wide range of fields. The current study is a comprehensive investigation of the performance of this detector against the photon beam. Moreover, a comparative study was carried out with other common detectors using the Mote Carlo code by the implementation of the same strategy. Material and Methods: During the simulation by FLUKA code, a number of photons were regarded as primary particles. It is attractive to trace each incident photon uniquely considering all possible collisions and produced secondary particles at the microdosimetry scale. In the current study, the coordinate of three-dimensional collisions location was realized at detector sensitive volume. Moreover, energy deposition was considered at each unique collision and through all interactions, totally. In addition, the physical concepts of photon interaction with detector volume were assessed, numerically. Furthermore, the effect of gold foils implemented as electrode at both sides of the detector was taken into account. Results: The obtained results indicated the context of photoelectric and Compton scattering in photon interactions with CZT, including the number of interactions, the deposited energy, and three-dimensional collision coordinate, while the latter case is proposed as a new achievement. Conclusion: As evidenced by the obtained results, the performance of this detector can be improved by changing material fraction and detector dimension to achieve optimum efficiency. In addition, the comparative results demonstrated that the efficiency of CZT covered by gold electrodes is superior to other common available semi-conductor detectors.

Energy-loss correction in charge sharing events for improved performance of pixellated compound semiconductors

The sharing of charge between multiple pixels can significantly degrade the energy resolution of small pixelated compound semiconductor detectors. This paper describes an energy calibration and reconstruction technique to correct for absorbed energy that is split over two neighbouring pixels, defined as bipixel events. Results were obtained with a 1 mm thick CdTe detector with 250 µm pixel pitch and an inter-pixel spacing of 50 µm, using the STFC HEXITEC ASIC. The proportion of charge sharing events was found to be 54% for photons at 59.5 keV when applying a noise threshold of 3 keV. Across the energy range investigated, bipixels were the predominant shared event type and the absolute fraction of shared events was found to be dependent on the noise threshold used. The reconstruction technique described reduces the degradation of energy resolution due to charge sharing in bipixel events compared to simple charge sharing summing techniques. This improved counting efficiency compared to using only isolated events and improved energy resolution compared to pixel addition techniques. When only isolated pixels were included, a FWHM energy resolution of 1.42 keV at 140.5 keV was achievable; inclusion of bipixel events using pixel addition results in an energy resolution of 3.33 keV whereas the reconstruction technique described here results in an energy resolution of 2.14 keV. When bipixel events are combined with single pixel events, the number of counts within the 140.5 keV photopeak of 99mTc increased by over 100%.

Improved spectroscopic performance in compound semiconductor detectors for high rate X-ray and gamma-ray imaging applications: A novel depth of interaction correction technique

In this paper results are presented for a novel charge loss correction algorithm that exploits the process of charge induction within compound semiconductor detectors. By detecting the residual induced signals in the pixels neighbouring an event, it is possible to correct for variation in the charge collection efficiency that occurs when high energy photons deposit charge at different depths in the detector. Results from 500μm pitch pixel detectors produced from both GaAs:Cr and high-flux-capable CdZnTe material readout using the STFC’s PIXIE ASIC are used to demonstrate the correction process across two different detector materials. The application of this depth of interaction correction results in a significant improvement in the FWHM of the 59.5 keV γ-ray photopeak in a 0.5 mm thick GaAs:Cr sensor from 14 keV to 4.7 keV. The application of the correction at the higher energy 122 keV γ-ray photopeak in a 2 mm thick CdZnTe detector also demonstrated an improvement from 4.0 keV to 2.7 keV.

Pulse-height loss in the signal readout circuit of compound semiconductor detectors

Compound semiconductor detectors such as CdTe, CdZnTe, HgI2 and TlBr are known to exhibit large variations in their charge collection times. This paper considers the effect of such variations on the measurement of induced charge pulses by using resistive feedback charge-sensitive preamplifiers. It is shown that, due to the finite decay-time constant of the preamplifiers, the capacitive decay during the signal readout leads to a variable deficit in the measurement of ballistic signals and a digital pulse processing method is employed to correct for it. The method is experimentally examined by using sampled pulses from a TlBr detector coupled to a charge-sensitive preamplifier with 150 μs of decay-time constant and 20 % improvement in the energy resolution of the detector at 662 keV is achieved. The implications of the capacitive decay on the correction of charge-trapping effect by using depth-sensing technique are also considered.

Comparison of experimental results of a Quad-CZT array detector, a NaI(Tl), a LaBr3(Ce), and a HPGe for safeguards applications

A compound semiconductor detector, CdTe (or CdZnTe), has been used in various areas including nuclear safeguards applications. To address its critical drawback, low detection efficiency, which leads to a long measurement time, a Quad-CZT array-based gamma-ray spectrometer in our previous study has been developed by combining four individual CZT detectors. We have re-designed the developed Quad-CZT array system to make it more simple and compact for a hand-held gamma-ray detector. The objective of this paper aims to compare the improved Quad-CZT array system with the traditional gamma-ray spectrometers (NaI(Tl), LaBr3(Ce), HPGe); these detectors currently have been the most commonly used for verification of nuclear materials. Nuclear materials in different physical forms in a nuclear facility of Korea were measured by the Quad-CZT array system and the existing gamma-ray detectors. For measurements of UO2 pellets and powders, and fresh fuel rods, the Quad-CZT array system turned out to be superior to the NaI(Tl) and LaBr3(Ce). For measurements of UF6 cylinders with a thick wall, the Quad-CZT array system and HPGe gave similar accuracy under the same measurement time. From the results of the field tests conducted, we can conclude that the improved Quad-CZT array system would be used as an alternative to HPGes and scintillation detectors for the purpose of increasing effectivenss and efficiency of safeguards applications. This is the first paper employing a multi-element CZT array detector for measurement of nuclear materials—particularly uranium in a UF6 cylinder—in a real nuclear facility. The present work also suggests that the multi-CZT array system described in this study would be one promising method to address a serious weakness of CZT-based radiation detection.

Optimizing timing performance of CdTe detectors for PET

Despite several attractive properties, the poor timing performance of compound semiconductor detectors such as CdTe and CdZnTe has hindered their use in commercial PET imaging systems. The standard method of pulse timing with such detectors is to employ a constant-fraction discriminator at the output of a timing filter which is fed by the pulses from a charge-sensitive preamplifier. The method has led to a time resolution of about 10 ns at full-width at half-maximum (FWHM) with 1 mm thick CdTe detectors. This paper presents a detailed investigation on the parameters limiting the timing performance of Ohmic contact planar CdTe detectors with the standard pulse timing method. The jitter and time-walk errors are studied through simulation and experimental measurements and it is revealed that the best timing results obtained with the standard timing method suffer from a significant loss of coincidence events (~50%). In order to improve the performance of the detectors with full detection efficiency, a new digital pulse timing method based on a simple pattern recognition technique was developed. A time resolution of 3.29 ± 0.10 ns (FWHM) in the energy range of 300–650 keV was achieved with an Ohmic contact planar CdTe detector (5 × 5 × 1 mm3). The digital pulse processing method was also used to correct for the charge-trapping effect and an improvement in the energy resolution from 4.83 ± 0.66% to 2.780 ± 0.002% (FWHM) at 511 keV was achieved. Further improvement of time resolution through a moderate cooling of the detector and the application of the method to other detector structures are also discussed.

Analog rise-time discriminator for CdZnTe detector

Due to variable time for charge collection, energy resolution of nuclear detectors declines, especially compound semiconductor detectors like cadmium zinc telluride (CdZnTe) detector. To solve this problem, an analog rise-time discriminator based on charge comparison principle is designed. The reference charge signal after attenuation is compared with the deconvoluted and delayed current signal. It is found that the amplitude of delayed current signal is higher than that of the reference charge signal when rise time of the input signal is shorter than the discrimination time, thus generating gating signal and triggering DMCA (digital multi-channel analyzer) to receive the total integral charge signal. When rise time of the input signal is longer than discrimination time, DMCA remains inactivated and the corresponding total integral charge signal is abandoned. Test results show that combination of the designed rise-time discriminator and DMCA can reduce hole tailing of CdZnTe detector significantly. Energy resolution of the system is 0.98%@662 keV, and it is still excellent under high counting rates.

The influence of electron track lengths on the γ-ray response of compound semiconductor detectors

The charge-trapping effect in compound semiconductor γ-ray detectors in the presence of a uniform electric field is commonly described by Hecht׳s relation. However, Hecht׳s relation ignores the geometrical spread of charge carriers caused by the finite range of primary and secondary electrons (δ-rays) in the detector. In this paper, a method based on the Shockley–Ramo theorem is developed to calculate γ-ray induced charge pulses by taking into account the charge-trapping effect associated with the geometrical spread of charge carriers. The method is then used to calculate the response of a planar CdTe detector to energetic γ-rays by which the influence of electron track lengths on the γ-ray response of the detectors is clearly shown.

EFFECT OF ALPHA IRRADIATION ON SILICON SCHOTTKY DIODE DETECTOR

This paper gives a brief overview of Semiconductor Schottky diode detector in response to α-particle irradiation. As α-particle are difficult to detect so we need a high resolution device for its detection. In this paper we have simulated a model of Si Schottky diode detector in Sentaurus TCAD Software. TCAD (Technology Computer Aided Design) simulation is a boon for the semiconductor devices. Using this tool we can simulate and design semiconductor devices and can generate simulation model to get the best optimum simulation results for semiconductor diode. Sentaurus TCAD supports wide range of semiconductor technologies from conventional to compound semiconductor detector. α-particles induced transient current pulse measurement were carried out on Si Schottky diode at (1) different temperature, (2) different energies of the incident α-particle and (3) different reverse bias of Schottky diode. Effect of temperature, incident α-particle and reverse bias on the generated αinduced transient current pulse were analyzed.

Collisional, radiative and total electron interaction in compound semiconductor detectors and solid state nuclear track detectors: Effective atomic number and electron density

Effective atomic numbers, Zeff and electron densities, Ne are widely used for characterization of interaction processes in radiation related studies. A variety of detectors are employed to detect different types of radiations i.e. photons and charged particles. In the present work, some compound semiconductor detectors (CSCD) and solid state nuclear track detectors (SSNTD) were investigated with respect to the partial as well as total electron interactions. Zeff and Ne of the given detectors were calculated for collisional, radiative and total electron interactions in the kinetic energy region 10keV–1GeV. Maximum values of Zeff and Ne were observed at higher kinetic energies of electrons. Significant variations in Zeff and Ne up to ≈20–25% were noticed for the detectors, GaN, ZnO, Amber and CR-39 for total electron interaction. Moreover, the obtained Zeff and Ne for electrons were compared to those obtained for photons in the entire energy region. Significant variations in Zeff were also noted not only for photons (up to ≈40% for GaN) but also between photons and electrons (up to ≈60% for CR-39) especially at lower energies. Except for the lower energies, Zeff and Ne keep more or less constant values for the given materials. The energy regions where Zeff and Ne keep constant clearly show the availability of using these parameters for characterization of the materials with respect to the radiation interaction processes.

Energy dispersive CdTe and CdZnTe detectors for spectral clinical CT and NDT applications

We are developing room temperature compound semiconductor detectors for applications in energy-resolved high-flux single x-ray photon-counting spectral computed tomography (CT), including functional imaging with nanoparticle contrast agents for medical applications and non-destructive testing (NDT) for security applications. Energy-resolved photon-counting can provide reduced patient dose through optimal energy weighting for a particular imaging task in CT, functional contrast enhancement through spectroscopic imaging of metal nanoparticles in CT, and compositional analysis through multiple basis function material decomposition in CT and NDT. These applications produce high input count rates from an x-ray generator delivered to the detector. Therefore, in order to achieve energy-resolved single photon counting in these applications, a high output count rate (OCR) for an energy-dispersive detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) compound semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel provided the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions, and at a sufficiently high detective quantum efficiency (DQE). We have developed high-flux energy-resolved photon-counting x-ray imaging array sensors using pixellated CdTe and CdZnTe semiconductors optimized for clinical CT and security NDT. We have also fabricated high-flux ASICs with a two dimensional (2D) array of inputs for readout from the sensors. The sensors are guard ring free and have a 2D array of pixels and can be tiled in 2D while preserving pixel pitch. The 2D ASICs have four energy bins with a linear energy response across sufficient dynamic range for clinical CT and some NDT applications. The ASICs can also be tiled in 2D and are designed to fit within the active area of the sensors. We have measured several important performance parameters including: the output count rate (OCR) in excess of 20 million counts per second per square mm with a minimum loss of counts due to pulse pile-up, an energy resolution of 7keV full width at half-maximum (FWHM) across the entire dynamic range, and a noise floor about 20keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdZnTe sensors incurring very little input capacitance to the ASICs. We present measurements of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, noise floor, as well as the temporal stability and uniformity under the rapidly varying high flux expected in CT and NDT applications.

Performance estimation of InSb compound semiconductor detectors as a function of active area using alpha particles

We have fabricated radiation detectors using p-type indium antimonide crystals grown by liquid phase epitaxy (LPE). The current–voltage curves, energy spectra of alpha particles, and energy resolutions obtained using two different InSb detectors were compared. The alpha-particle energy resolutions were 1.8% at 24 and 42K, using the LPE–InSb detector with wafer size of 1.0×1.5mm2.

Alpha-ray spectrometry at high temperature by using a compound semiconductor detector

The use of conventional radiation detectors in harsh environments is limited by radiation damage to detector materials and by temperature constraints. We fabricated a wide-band gap semiconductor radiation detector based on silicon carbide. All the detector components were considered for an application in a high temperature environment like a nuclear reactor core. The radiation response, especially to alpha particles, was measured using an 241Am source at variable operating voltages at room temperature in the air. The temperature on detector was controlled from 30°C to 250°C. The alpha-particle spectra were measured at zero bias operation. Even though the detector is operated at high temperature, the energy resolution as a function of temperature is almost constant within 3.5% deviation.

Use of commercial operational amplifiers in a low cost multi-channel preamplifier system

We report on a simple, compact-size and cost-effective multi-channel charge-sensitive preamplifier system using the commercial IC operational amplifiers. An energy resolution of 5.6% at 511keV is achieved with a large size (10×10×1mm3) planar CdTe detector. The system is well suited for use with the compound semiconductor detectors in the applications in which the rather high power consumption of the system (320mW per channel) can be tolerated.

Photon detection by an InSb compound semiconductor detector with reduced leakage current

An InSb detector was fabricated using a liquid phase epitaxially grown crystal. By changing the electrode structure design, the leakage current of the detector was reduced. In addition, the result of 137Cs-gamma-ray measurement was discussed with a charge collection model with using a modified Hecht's equation.

K-mean clustering algorithm for processing signals from compound semiconductor detectors

Abstract The K-mean clustering algorithm was employed for processing signal waveforms from TlBr detectors. The signal waveforms were classified based on its shape reflecting the charge collection process in the detector. The classified signal waveforms were processed individually to suppress the pulse height variation of signals due to the charge collection loss. The obtained energy resolution of a 137 Cs spectrum measured with a 0.5 mm thick TlBr detector was 1.3% FWHM by employing 500 clusters.

Digital signal processing method based on Maxi-Mini distance algorithm

A fast digital signal processing method for numerical analysis of individual signals from CdZnTe compound semiconductor detectors is introduced in this paper. Using Maximum-Minimum (Maxi-Mini) Distance Algorithm, a parametric approach has been used for classifying the waveforms into a set of clusters, each has a similar signal shape with a corresponding pulse height spectrum. A corrected total pulse height spectrum was obtained by applying a normalisation factor for the full-energy peak for each cluster with much improvement in the energy spectrum characteristics. This method is applied successfully for a real measured data and can be applied to any detector that suffers from signal shape variation.

Averaged Currents Induced by Alpha Particles in an InSb Compound Semiconductor Detector

Very fast pulses due to alpha particle incidence were observed by an undoped-type InSb Schottoky detector. This InSb detector was operated without applying bias voltage and its depletion layer thickness was less than the range of alpha particles. The averaged current induced by alpha particles was analyzed as a function of operating temperature and was shown to be proportional to the Hall mobility of InSb.