Charge trapping effects in cryogenic particle detectors made using single-crystal semiconductor substrates

We explore charge-trapping effects in cryogenic particle detectors composed of single-crystal silicon substrates with both titanium transition-edge sensors (TES) and charge-collection electrodes deposited upon them. These effects include transients on various time scales which follow the evolution of different kinds of space charge, intrinsic gain and linearity shifts in signals characteristic of changes in the absorption of energy carried by electrons and holes, variations in charge-collection efficiency and ionization resolution, etc., The physics involved, relevant for many other cryogenic, semiconductor-based devices, includes a variety of charge trapping and transport mechanisms.     

Improving the radiation resistance of semiconductor detectors of radioactive radiation

The possibility of using semiconductor detectors not containing potential barriers (p-n junctions) to measure the intensity radioactive radiation fluxes causing degradation of the electric parameters of detector material is theoretically substantiated. The assumptions are confirmed by experimental results.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 61–63, January, 1994.     

A method of processing the signals from ionizing radiation detectors

A nonlinear sensor is described, the required characteristic of which is achieved by using digital processing of the flux of random pulses, having a Poisson distribution, the parameter of which may vary over a wide range. The form of the characteristic is determined by the distribution function of the pulses of the internal generator. __________ Translated from Izmeritel’naya Tekhnika No. 4, pp. 61–63, April, 2007.     

Principles and new developments of semiconductor radiation detectors

The physics aspects of semiconductor radiation detectors are briefly reviewed. A comparison with other radiation detectors, in particular with wire chambers, shows the unique features of the advanced semiconductor detectors of high density, high ionisation density and the possibility of drift field shaping using space charges. Novel applications and device arrangements are discussed.     

Energy transfer by radiation in a lumpy layer

Energy transfer by radiation in a layer of lumpy material is examined, A formula is derived for the effective coefficient of heat conduction of the layer for radiation heat transfer.Notation I, K opposing radiant fluxes, W/m² - a _c, r_c, d_c layer absorptivity, reflectivity and transmissivity - a _p.th, d₀ transmissivity for radiant energy passing directly through the layer and after reflection from the layer material - _c emissivity - r material reflectivity - L layer thickness, m - h distance between separate interlayers, m - T temperature, °K - q_r resultant radiant flux in the layer, W/m2 - _eff effective coefficient of radiation heat conduction of the layer, W/m · deg - angular coefficient from one base of the hole to the other - f₀ magnitude of the hole area in the plate, m²/m² - p porosity - E_{incident k} magnitude of incident radiant fluxes on the plate k Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 796–801, May, 1971.     

Heat transfer in a layer in the presence of moving heat sources

The problem regarding the distribution of temperatures is solved for the case of a layer in which a combustion front is moving at a constant speed, said front caused by the burnout of a fuel uniformly distributed through the layer.     

Charge trapping and luminance mechanisms of organic light-emitting devices with a 5,6,11,12-tetraphenylnaphthacene emission layer

The electrical and the optical properties of the organic light-emitting devices fabricated utilizing a 5,6,11,12-tetraphenylnaphthacene (rubrene) emission layer (EML) were investigated to clarify their charge trapping and luminance mechanisms. The increase in the thickness of the rubrene EML extended the width of the recombination zone, resulting in the enhancement of the efficiency and in the variation of the shoulder peak intensity of the electroluminescence spectra. The charge trapping and luminance mechanisms were affected by the total thickness of the rubrene layer, regardless of the existence of the barrier layers. The charge trapping and luminance mechanisms are described on the basis of the experimental results.     

Characterization of bismuth tri-iodide single crystals for wide band-gap semiconductor radiation detectors

Bismuth tri-iodide is a wide band-gap semiconductor material that may be able to operate as a radiation detector without any cooling mechanism. This material has a higher effective atomic number than germanium and CdZnTe, and thus should have a higher gamma-ray detection efficiency, particularly for moderate and high energy gamma-rays. Unfortunately, not much is known about bismuth tri-iodide, and the general properties of the material need to be investigated. Bismuth tri-iodide does not suffer from some of the material issues, such as a solid state phase transition and dissociation in air, that mercuric iodide (another high-Z, wide band-gap semiconductor) does. Thus, bismuth tri-iodide is both easier to grow and handle than mercuric iodide. A modified vertical Bridgman growth technique is being used to grow large, single bismuth tri-iodide crystals. Zone refining is being performed to purify the starting material and increase the resistivity of the crystals. The single crystals being grown are typically several hundred mm³. The larger crystals grown are approximately 2 cm³. Initial detectors are being fabricated using both gold and palladium electrodes and palladium wire. The electron mobility measured using an alpha source was determined to be 260±50 cm²/Vs. An alpha spectrum was recorded with one of the devices; however the detector appears to suffer from polarization.     

Performance enhancements of compound semiconductor radiation detectors using digital pulse processing techniques

The potential benefits of using compound semiconductors for X-ray and gamma ray spectroscopy are already well known. Radiation detectors based on high atomic number and wide band gap compound semiconductors show high detection efficiency and good spectroscopic performance even at room temperature. Despite these appealing properties, incomplete charge collection is a critical issue. Generally, incomplete charge collection, mainly due to the poor transport properties of the holes, produces energy resolution worsening and the well known hole tailing in the measured spectra. In this work, we present a digital pulse processing (DPP) system for high resolution spectroscopy with compound semiconductor radiation detectors. The DPP method, implemented on a PC platform, performs a height and shape analysis of the detector pulses (preamplifier output pulses), digitized by a 14-bit, 100 MHz ADC. Fast and slow shaping, automatic pole-zero adjustment, baseline restoration and pile-up rejection allow precise pulse height measurements both at low and high counting rate environments. Pulse shape analysis techniques (pulse shape discrimination, linear and nonlinear pulse shape corrections) to compensate for incomplete charge collection were also implemented. The results of spectroscopic measurements on a planar CdTe detector show the high potentialities of the system, obtaining low tailing in the measured spectra and energy resolution quite close to the theoretical limit. High-rate measurements (up to 820 kcps) exhibit the excellent performance of the pulse height analysis and the benefits of pulse shape techniques for peak pile-up reduction in the measured spectra. This work was carried out in the framework of the development of portable X-ray spectrometers for both laboratory research and medical applications.     

Schottky and pn junction cryogenic radiation detectors made of p-InSb compound semiconductor

Schottky and pn junction detectors were fabricated with p-InSb. Fabrication methods, energy spectra of ²⁴¹Am alpha particles and rise times are shown. We could observe pulses at operating temperatures up to 77 and 115 K for the Schottky and the pn junction detectors, respectively.     

Application of position-sensitive semiconductor detectors in a magnetic beta-spectrometer

The possibility to use continuous position-sensitive semiconductor detectors for a magnetic beta-spectrometer of the π√2 type is shown. The momentum resolution of the spectrometer for the electron energy region of 300–1000 keV is Δp/p = 0.2–0.3%. Monte Carlo calculations of electron multiple scattering in silicon are made and its influence on position resolution is shown.     

Investigation of boundary layer stability in the presence of intense heat transfer

The results of an investigation of the transition of a laminar boundary layer to turbulent in the air behind a shock wave by the thin-film thermometry method are presented. Stabilization of transition Reynolds number is observed with an increase of the intensity of heat transfer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 1, pp. 29–33, July, 1971.     

Formation of color centers in a thin layer of LiF crystals under VUV radiation from a barrier discharge

Under radiation from a barrier discharge, luminescent color centers are formed in a surface layer of lithium fluoride crystal served as a dielectric barrier. Analysis of the damping kinetics and luminescence spectra has revealed these centers to be F ₃ ⁺ and F ₂ centers. Structural defects are mainly formed via the photon-induced mechanism (i.e., defects are formed due to the generation of electron-hole pairs as a result of absorption of photons of barrier-discharge radiation). Barrier discharge in different gases can be successfully used to form thin layers containing luminescence centers on the surface of transparent insulators for various scientific and practical applications.     

Dependence of electron and hole lifetimes on the majority recombination impurity concentration in the presence of auxiliary carrier trapping centers

It has been shown that a substantial increase in carrier lifetimes in a certain range of increasing concentration of recombination impurities may also take place in the presence of auxiliary (background) deep impurities, and two maxima may even be observed. Pis’ma Zh. Tekh. Fiz. 23, 58–63 (December 26, 1997)     

The effect on the tensile properties of PIP-processed SiC/SiC composite of a chemical vapor-infiltrated SiC layer overlaid on the pyrocarbon interface layer

A chemical vapor-infiltrated (CVI) SiC layer is often deposited on the pyrocarbon (PyC) fiber–matrix interface layer in SiC fiber-reinforced SiC matrix (SiC/SiC) composites. It is normally applied to protect the PyC layer from reacting with molten Si or sintering aids during manufacturing, and to guard against the effects of high temperature, oxidation and moisture during use. In this study, we investigated the effect of this SiC layer on the tensile properties of a composite. Tensile tests of our composite samples showed the SiC layer to have no noticeable effects on its ultimate load or fracture strain, whereas it decreased the load-to-strain ratio and proportional limit. The test results were analyzed by carrying out element tests on filaments and fiber bundle samples, fracture mirror analysis of pullout fibers, and finite element analysis (FEA) of residual thermal stress around the interface.     

Modelling radiation loads to detectors in a SNAP mission

In order to investigate the degradation of optical detectors of the Supernova Acceleration Project (SNAP) space mission because of irradiation, a three-dimensional model of the satellite has been developed. A realistic radiation environment at the satellite orbit, including both galactic cosmic rays and cosmic ray trapped in radiation belts, has been taken into account. The modelling has been performed with the MARS14 Monte Carlo code. In a current design, the main contribution to dose accumulated in the photo-detectors is shown to be due to trapped protons. The contribution of primary alpha particles is estimated. Predicted performance degradation for the photodetector for a four-year space mission is 40% and this can be reduced further by means of shielding optimisation.     

Characterization of trapping force in the presence of spherical aberration

Abstract

Transverse trapping force in laser tweezers is investigated in the presence of spherical aberration caused by the refractive-index mismatch between a cover slip and the water solution where particles are suspended. The transverse trapping efficiency is characterized in terms of the numerical aperture of a microscope objective and the thickness of a sample cell. It has been experimentally demonstrated that the spherical aberration can be compensated for by changing the effective tube length of an objective used for trapping. As a result, the transverse trapping efficiency can be improved by up to 20%. In principle, a further improvement in the trapping efficiency is possible if an objective of an infinitely-long tube length is used.