Design of the readout electronics for the DAMPE Silicon Tracker detector

The Silicon Tracker (STK) is one of the detectors of the DAMPE satellite used to measure the incidence direction of high energy cosmic rays. It consists of 6 X-Y double layers of silicon micro-strip detectors with 73728 readout channels. It is a great challenge to read out the channels and process the huge volume of data in the harsh environment of space. 1152 Application Specific Integrated Circuits (ASIC) and 384 ADCs are used to read out the detector channels. 192 Tracker Front-end Hybrid (TFH) modules and 8 identical Tracker Readout Board (TRB) modules are designed to control and digitalize the front signals. In this paper, the design of the readout electronics for the STK and its performance are presented in detail.     

Survey meter combining CVD diamond and silicon detectors for wide range of dose rates and high accumulated doses

We have developed a prototype of a survey meter combining a CVD diamond detector and silicon detectors to appropriately take temporal measurements of γ-ray radiations over a wide range of the dose rates and to measure high accumulated doses of γ-ray radiations. In order to carry out this, at first, we have studied the radiation hardness of diamond detectors suitably fabricated with high-quality single-crystalline CVD diamond films to confirm that such CVD diamond detectors have greatly superior radiation hardness, compared with commercially available silicon detectors. It is evidenced that the performance of the CVD diamond detector did not significantly change even after heavy γ-ray irradiation of 0.7 MGy while the silicon detectors have a remarkable increase in the dark current, a detection peak shift to the low energy side, and a decrease in detection counts for 5.486-MeV α particles. Due to a size limitation of the CVD diamond detector, such a CVD diamond detector was combined with six commercially available silicon detectors to fabricate a survey meter which can appropriately work under severe irradiation conditions, or, at accumulated doses larger than at least 0.5 MGy and which can cover a wide range of the dose rates from 1 μGy/h to at least 1 kGy/h. The prototype survey meter had a practically useful linearity in this dose rate range. Thus, we have confirmed that such a diamond-Si combined survey meter can be put into practical use.     

Low capacitance CMOS silicon photodetectors for optical clock injection

We have studied the response of CMOS compatible detectors fabricated in a silicon-on-sapphire (SOS) process, operated under short pulse excitation in the blue. These high speed, low capacitance detectors would be suitable for very precise, surface-normal clock injection with silicon CMOS. We characterize the capacitance of the detector structure through a combination of experimental techniques and circuit-level and electromagnetic simulations. The transit-time-limited response of the detectors is validated through pump–probe experiments. Detector response times of ∼35 ps have been measured, and devices have capacitance as low as ∼4 fF.     

Role of guard rings in improving the performance of silicon detectors

BARC has developed large-area silicon detectors in collaboration with BEL to be used in the pre-shower detector of the CMS experiment at CERN. The use of floating guard rings (FGR) in improving breakdown voltage and reducing leakage current of silicon detectors is well-known. In the present work, it has been demonstrated that FGRs can also be used to improve the spectroscopic response of silicon detectors. The results have been confirmed by carrying outα-particle (≈5 MeV) andγ-ray (60 keV) spectroscopies with the FGR floating or biased and the underlying physics aspect behind the change in spectra is explained. Although reduction in leakage current after biasing one of the guard rings has been reported earlier, the role of a guard ring in improving the spectroscopic response is reported for the first time. Results of TCAD simulations for silicon detectors with the guard ring under different biasing conditions have been presented. Low yield in producing large-area silicon detectors makes them very costly. However, with one of the FGRs biased even a detector having large surface leakage current can be used to give the same response as a very good detector. This makes the use of large-area silicon detectors very economical as the yield would be very high (>90%).     

一种新型高功率微波探测器

 叙述了基于P型硅半导体中的热载流子效应研制成功的一种单脉冲高功率微波探测器。这种高功率微波探测器具有承受微波功率高(比普通检波器高近六个量级)、时间响应快(响应时间小于2.0ns)等特点。探测器由P型硅传感单元和标准波导组成,其工作频率范围为波导的工作频率范围,根据不同需求可以在3.0GHz至30GHz的频率范围内制作成多种不同型号的探测器。也给出了工作在X波段的这种探测器的标定方法和标定结果,标定结果表明探测器的输出信号幅度正比于注入微波功率,输出电压值可达10V。该探测器很适合于高功率微波峰值功率测量,尤其在电磁干扰环境中具有优势,为解决目前高功率微波功率测量不准的技术难题提供了一种有效的技术手段。     

A multilayer ΔE-ER telescope for breakup reactions at energies around the Coulomb barrier

The breakup reactions of weakly-bound nuclei at energies around the Coulomb barrier and the corresponding coupling effect on the other reaction channels are hot topics nowadays. To overcome the difficulty in identifying both heavier and lighter fragments simultaneously, a new kind of ionization-chamber based detector telescope has been designed and manufactured. It consists of a PCB ionization chamber and three different thickness silicon detectors installed inside the chamber, which form a multilayer ΔE-E_R telescope. The working conditions were surveyed by using an α source. An in-beam test experiment shows that the detector has good particle identification for heavy particles like ¹⁷F and ¹⁶O as well as light particles like protons and alpha particles. The measured quasi-elastic scattering angular distribution and the related discussions for ¹⁷F+²⁰⁸Pb are presented.     

Current-voltage behaviour of Schottky diodes fabricated on p-type silicon for radiation hard detectors

Current-voltage (I-V) measurements were carried out on Schottky diodes fabricated on undoped and on metal-doped p-type silicon. The metals used are gold, platinum, erbium and niobium. The I-V data were used to extract the saturation current, the ideality factor and the Schottky barrier height for each of the five diodes. These parameters were correlated to the defect levels generated by the metals in silicon. The results show that in all cases the silicon has become relaxation-like after doping since the device current is Ohmic. This is in agreement with the existence of the midgap defect in all the doped devices as compiled from the literature. Such metal doped (or relaxation) devices have been found to perform better as radiation-hard particle detectors.     

Unitary models of single detector triggering and local position measurements

Recent work by Wan and McLean has shown that all quantum measurements may be reduced to local position measurements. Using an array of particle detectors as the measuring apparatus we show how a model employing superselection rules and unitary evolution leads to a single detector triggering in each act of measurement. We also present an explicit model of particle detection as a unitary ionization process producing a single ion in the detector, subsequent amplification of which to the visible can be described adequately in classical terms.     

A versatile Monte Carlo package for computation of efficiencies of Si(Li), SDD and Ge detectors

Currently, most detector efficiency calculations for X‐ray detectors assume that the source is a point source on the axis of symmetry of the detector, but this is not always accurate. We have devised a Monte Carlo program to simulate photon transport in Si(Li), SDD and planar Ge detectors that natively handles finite, tilted and off‐axis sources. Although electron transport is not handled at this stage, photon transport is completely handled, including absorption from filters and multiple scattering in the detector crystal. The K escape peak is handled for both silicon and germanium detectors, and the L escape peak is also handled for germanium detectors. Our efficiency results compare very well with previous work when idealized systems are simulated, and the effect of a non‐idealized system is presented. Escape peak intensity ratios are given for both silicon detectors (K peak only) and germanium detectors (K and L peaks), and the results for the K escape peaks agree well with previous work. Results are presented for a recent annular detector system, which is a good example of systems that are poorly handled under previous efficiency calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Silicon detector technology development in India for the participation in international experiments

A specific research and development program has been carried out by BARC in India to develop the technology for large area silicon strip detectors for application in nuclear and high energy physics experiments. These strip detectors will be used as pre-shower detector in the CMS experiment at LHC, CERN for π ⁰/λ rejection. The fabrication technology to produce silicon strip detectors with very good uniformity over a large area of ∼40 cm², low leakage currents of the order of 10 nA/cm² per strip and high breakdown voltage of >500 V has been developed by BARC. The production of detectors is already under way to deliver 1000 detector modules for the CMS and 90% production is completed. In this paper, research and development work carried out to develop the detector fabrication technology is briefly described. The performance of the silicon strip detectors produced in India is presented. The present status of the detector technology is discussed.      

Ultraviolet photoconductive detector based on Al doped ZnO films prepared by sol-gel method

We report a study on the fabrication and characterization of ultraviolet photodetectors based on ZnO:Al films. Using sol-gel technique, highly c-axis oriented ZnO films with 5 mol% Al doping were deposited on Si(1 1 1) substrates. The photoconductive UV detectors based on ZnO:Al thin films, having a metal-semiconductor-metal (MSM) structure with interdigital (IDT) configuration, were fabricated by using Au as a contact metal. The characteristics of dark and photocurrent of the UV detector and the UV photoresponse of the detector were investigated. The linear current-voltage (I-V) characteristics under both forward and reverse bias exhibit ohmic metal-semiconductor contacts. Under illumination using monochromatic light with a wavelength of 350 nm, photo-generated current was measured at 58.05 μA at a bias of 6 V. The detector exhibits an evident wide-range spectral responsivity and shows a trend similar to that in transmittance and photoluminescence spectrum.     

The microdosimetric one-hit detector model for calculating the response of solid state detectors

The microdosimetric one-hit detector model has been developed and applied to calculate the dose response, energy response and relative efficiency of thermoluminescent LiF:Mg,Cu,P and CaF₂:Tm detectors, and of the free-radical alanine dosimeter, after their exposure to radiation of different quality. The one-hit detector is described by two model parameters: the target diameter, d and the saturation parameter, α. Combining these parameters with microdosimetric distributions in nanometer-size targets calculated using Monte Carlo track structure codes TRION and MOCA-14, it was possible to describe and predict a great variety of experimental data for photon, X-ray, beta-electron, proton, alpha-particles and heavy ion irradiation. Within the framework of this biophysical model of radiation action, some mechanistic insight into the physics of radiation action in solid state detectors can be obtained.     

Using pixel detectors in investigations of EC/EC decay

A new multi-detector spectrometer based on Timepix silicon pixel detectors is developed to investigate the 2νEC/EC decay of ¹⁰⁶Cd. The detectors have high efficiency for recording two low-energy KX radiation quanta emitted during 2νEC/EC decay. The ability of pixel detector to identify α, β, and γ particles and precisely localize them allows us to suppress background radiation efficiently. Test measurements for an assembly of two pixel detectors in an underground laboratory were performed. They showed the possibility of using them in the search for the 2νEC/EC decay of ¹⁰⁶Cd.     

Trapped modes in finite quantum waveguides

The eigenstates of an electron in an infinite quantum waveguide (e.g., a bent strip or a twisted tube) are often trapped or localized in a bounded region that prohibits the electron transmission through the waveguide at the corresponding energies. We revisit this statement for resonators with long but finite branches that we call ??finite waveguides??. Although the Laplace operator in bounded domains has no continuous spectrum and all eigenfunctions have finite L ₂ norm, the trapping of an eigenfunction can be understood as its exponential decay inside the branches. We describe a general variational formalism for detecting trapped modes in such resonators. For finite waveguides with general cylindrical branches, we obtain a sufficient condition which determines the minimal length of branches for getting a trapped eigenmode. Varying the branch lengths may switch certain eigenmodes from non-trapped to trapped or, equivalently, the waveguide state from conducting to insulating. These concepts are illustrated for several typical waveguides (L-shape, bent strip, crossing of two strips, etc.). We conclude that the well-established theory of trapping in infinite waveguides may be incomplete and require further development for applications to finite-size microscopic quantum devices.     

The investigation of noise in hard radiation detectors by pulse-amplitude analysis

The potentialities of pulse-amplitude analysis for noise measurements are demonstrated with p ⁺-n silicon detectors. It is suggested to use the detector current as a parameter and vary it by illuminating the samples. The instrument was calibrated by the shot noise of the photocurrent. The criteria for shot noise are the linearity of the noise squared vs. current dependence and its slope. It is shown that conventional instrumentation for pulse-amplitude analysis provides accurate yet rapid noise investigation. For the detectors studied, flicker noise was absent even when the trapped charge in the field oxide increases by one order of magnitude.     

Planar sulfur-doped silicon detectors for high-speed infrared thermography

Planar extrinsic sulfur-doped silicon detectors for infrared (IR) semiconductor-discharge gap image converters intended for use in high-speed thermography of remote objects have been developed. The detectors were fabricated by high-temperature diffusion of sulfur into silicon wafers from the vapor phase. The dependence of doping efficiency on the sulfur vapor pressure in the course of diffusion was analyzed. The detector fabrication technology was optimized to meet the specific requirements for their operation in the microdischarge devices considered. The detectors were tested in a laboratory setup comprising a blackbody source of IR light, an image converter, and a pulsed CCD camera for recording the converted images. The converter equipped with the detector can provide imaging of objects heated to a temperature, T_min ≈ 200 °C, with a temporal resolution on the order of 10^?6 s and spatial resolution of about 5 lines/mm.     

Theoretical concepts of operation of a semiconductor detector based on a <Emphasis Type="Italic">p-n</Emphasis> junction

Collected charge originating in a semiconductor detector of the p⁺-n-n⁺ type as a result of interaction with a monoenergetic electron beam with energies in the range from 7 to 25 keV is calculated. Generation of electron-hole pairs (EHPs) is calculated using the Monte Carlo method. In the context of the diffusion-drift model, an analytic expression for the contribution of generated EHPs to the detected signal is derived. It is shown that the losses of charge to recombination in the course of transport significantly affect the shape of detected signal. The comparison of simulated energy spectra with experimentally measured spectra shows good agreement between theory and experiment. Thus, the basics of a theoretical approach that makes it possible to calculate the operational characteristics of semiconductor detectors are developed; as a result, the parameters of these detectors can be optimized in designing the practically important semiconductor proportional detectors to be used in analytical methods.     

Modulation of breathers in cigar-shaped Bose-Einstein condensates

We present new solutions to the nonautonomous nonlinear Schrödinger equation that may be realized through convenient manipulation of Bose-Einstein condensates. The procedure is based on the modulation of breathers through an analytical study of the one-dimensional Gross-Pitaevskii equation, which is known to offer a good theoretical model to describe quasi-one-dimensional cigar-shaped condensates. Using a specific ansatz, we transform the nonautonomous nonlinear equation into an autonomous one, which engenders composed states corresponding to solutions localized in space, with an oscillating behavior in time. Numerical simulations confirm stability of the modulated breathers against random perturbation on the input profile of the solutions.     

High-performance UV detector based on Ga-doped zinc oxide thin films

High-quality ultraviolet photoconductive detectors have been fabricated using Ga-doped zinc oxide layers grown by spray pyrolysis on glass substrates. The performance of the photoconductivity has been tested by the measurements of the current-voltage (I-V) characteristics under forward and reverse bias. The devices have been characterized to investigate the effect of buffer layer on the detector performances. The behaviour of photocurrent with respect to optical power density, wavelength and chopping time has been investigated. We achieved the highest responsivity of about 1125 A/W at 5 V bias at 365 nm peak wavelength. Our approach provides a simple and cost-effective way to fabricate high-performance ‘visible-blind’ UV detectors.     

Dual-band pixelless upconversion imaging devices

We have proposed a type of mid-infrared (MIR) and far-infrared (FIR) dual-band imaging device, which employs the photon frequency upconversion concept in a GaN/AlGaN MIR and FIR dual-band detector integrated with a GaN/AlGaN violet light emitting diode. On the basis of the photoresponse of single-period GaN/AlGaN dual-band detectors, we present the detailed optimization of multiperiod GaN emitter/AlGaN barrier detectors and their applications to dual-band pixelless upconversion imaging. Satisfying images have been received through the analysis of the modulation transfer function and the upconversion efficiency in the GaN/AlGaN dual-band pixelless upconverters, which exhibit good image resolution, high quantum efficiency, and negligible cross talk.