We present a comprehensive review of the properties of the epitaxial 4H silicon carbide polytype (4H–SiC). Particular emphasis is placed on those aspects of this material related to room, high-temperature and harsh environment ionizing radiation detector operation. A review of the characterization methods and electrical contacting issues and how these are related to detector performance is presented. The most recent data on charge transport parameters across the Schottky barrier and how these are related to radiation spectrometer performance are presented. Experimental results on pixel detectors having equivalent noise energies of 144 eV FWHM (7.8 electrons rms) and 196 eV FWHM at +27 °C and +100 °C, respectively, are reported. Results of studying the radiation resistance of 4H–SiC are analysed. The data on the ionization energies, capture cross section, deep-level centre concentrations and their plausible structures formed in SiC as a result of irradiation with various particles are reviewed. The emphasis is placed on the study of the 1 MeV neutron irradiation, since these thermal particles seem to play the main role in the detector degradation. An accurate electrical characterization of the induced deep-level centres by means of PICTS technique has allowed one to identify which play the main role in the detector degradation.

https://iopscience.iop.org/article/10.1088/0957-0233/19/10/102001/pdf

Silicon carbide and its use as a radiation detector material

New developments in theoretical studies of defects and impurities in III-Nitrides as pertinent to compensation and recombination in these materials are discussed. New results on experimental studies on defect states of Si, O, Mg, C, Fe in GaN, InGaN, and AlGaN are surveyed. Deep electron and hole traps data reported for GaN and AlGaN are critically assessed. The role of deep defects in trapping in AlGaN/GaN, InAlN/GaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed. The recent data on deep traps influence on luminescent efficiency and degradation of characteristics of III-Nitride light emitting devices and laser diodes are reviewed.

Deep traps in GaN-based structures as affecting the performance of GaN devices

The traditional compensation model to explain the high resistivity properties of CdTe is based on the presence of a deep acceptor level of the cadmium vacancy in the middle of the band gap. A new compensation model based on a deep intrinsic donor level is presented. The compensation model is used together with an appropriate segregation model to calculate axial distributions of resistivity which are compared with spatially resolved resistivity measurements. The Te-antisite defect is discussed as a possible origin cause of this intrinsic defect, which is also supported by theoretical calculations.

Modified compensation model of CdTe

A sensitive photoinduced current transient spectroscopy technique using a computer for data acquisition and processing has been worked out It enables one to determine separately the signatures and concentrations of deep levels in high‐resistivity bulk materials In a previous paper, possible signal processing has been analyzed from a rather theoretical point of view In the present report, the instrumentation used as well as the experimental procedure and some practical and complementary aspects will be discussed For the determination of reliable trap signatures, we have proposed and tested a four‐gate data treatment that eliminates, or at least reduces, many of the problems encountered when using the usual double‐gate procedure provided some experimental precautions are taken Yet the double‐gate method is useful when one wants to estimate the trap concentrations A standard experimental procedure is presented that takes into account the temperature dependence of the mobility/free‐lifetime product of thermal emitted carriers, and its possible variation during the relaxation of the traps

Photoinduced current transient spectroscopy in high‐resistivity bulk materials: Instrumentation and methodology

Photo-induced current transient spectroscopic study of the traps in CdTe

An experimental arrangement is described by which emission coefficient behavior associated with deep‐level traps in semi‐insulating GaAs can be surveyed, from the photoconductive transient behavior following a trap‐filling light pulse. This method, often referred to as PITS (for photoinduced transient spectroscopy) has analogies with the transient capacitance spectroscopy usable for conductive material, but some significant differences also. The necessary experimental precautions which can maximize the probability of getting reliable data are described, and illustrated by PITS results obtained with bulk semi‐insulating samples of Cr‐doped GaAs. Those results include data for five kinds of trap with activation energies from 0.3 to 0.8 eV, of which some are readily identifiable and others are not. The method described in this paper relies on analog measurement of the change in sample voltage during a specified time interval of the photoconductive decay.

Transient photoconductivity measurements in semi‐insulating GaAs. I. An analog approach

We describe an experimental setup designed to study photoconductive transients in semi‐insulating materials. The method, known as photoinduced transient spectroscopy, is based on a digital signal‐averaging technique. Although this digital method eliminates or reduces many of the experimental problems encountered when using an analog approach, several new problems arise. The method is described, and the difficulties are illustrated using data obtained from both Cr‐doped and nominally undoped samples of GaAs.

J. S. Blakemore

Papers

Transient photoconductivity measurements in semi‐insulating GaAs. I. An analog approach

Transient photoconductivity measurements in semi-insulating GaAs II: A digital approach