V. Kazukauskas

Performance of irradiated bulk SiC detectors

Abstract Silicon carbide (SiC) is a wide bandgap material with many excellent properties for future use as a detector medium. We present here the performance of irradiated planar detector diodes made from 100-μm-thick semi-insulating SiC from Cree. Ohmic/Schottky diodes were produced and characterised using Schottky barrier measurements and charge collection efficiency (CCE) measurements were made for 5.48 MeV 241 Am alpha particles. Charge collection of ∼60% was measured initially. Measurements were taken of trap lifetimes in an effort to understand this. Three distinct traps with lifetimes of 4, 16, and 130 s were found. Irradiation took place at Paul Scherrer Institute (PSI) to fluences of 10 12 , 10 13 , and 5×10 14 cm −2 , with 300 MeV /c pions. Changes in the Schottky barrier height, leakage current, trap lifetimes, and CCE measurements give an indication of the possible degradation in performance of detectors of this type over their projected lifetime.

A New Radiation Hard Semiconductor — Semi‐Insulating GaN: Photoelectric Properties

The anticipated upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses a severe challenge to semiconductor detectors in the CERN experiments. The suitability of semi‐insulating GaN (SI‐GaN), proposed as an alternative to silicon for the fabrication of radiation hard detectors, is investigated here in MOCVD GaN layers grown on sapphire. The electrical properties of SI‐GaN were studied by dc and microwave techniques, and defect parameters determined by the method of thermally stimulated currents. Variations of charge collection efficiency (CCE) in SI‐GaN diodes induced by ionizing radiation of 5.48 MeV alpha particles were revealed. Samples were also irradiated by X‐rays, reactor neutrons and high‐energy proton fluences of up to 1016 cm−2. The high radiation hardness of SI‐GaN was demonstrated by the modest reduction in CCE, from 92% to 77%, in the material irradiated by neutrons (up to a fluence of 1015 cm−2). The CCE was unaffected by an X‐rays dose of 600 MRad), but decreased to a few % after proton and neutron fluences of 1016 cm−2. The electrical characteristics vary more significantly, depending on irradiation type and dose. Fast decay components and a significant role of percolation effects are observed in the photoconductivity transients.

Characterisation of semiconductor materials for ionising radiation detectors

Abstract Methods for the detection and characterisation of semiconductor material parameters and inhomogeneities are analysed. The peculiarities of different “classical” material and structure characterisation methods are discussed. The methods of lifetime and surface recombination mapping and electric field distribution in the samples are presented. Some results of investigations of GaAs, Si and SiC are used for the characterisation of different peculiarities or methods.

Analysis of trap spectra in LEC and epitaxial GaAs

Abstract Different methods of trap parameter measurement are analysed. Transient photoconductivity and thermally stimulated effects were used to investigate the influence of traps in LEC SI-GaAs and high-resistivity epitaxial GaAs. The peculiarities of the TSC were analysed and shown to be related to the influence of crystal micro-inhomogeneities.

Defects and radiation damage in semi-insulating GaAs radiation detectors

Abstract Thermally stimulated current (TSC) and depolarisation (TSD), measurements and detailed analysis of current - voltage ( I - V ) characteristics have been made on semi-insulating GaAs (SI-GaAs) Schottky diode particle detectors, fabricated on substrates from several suppliers, before and after irradiation with high-energy protons and pions. The analysis of I - V characteristics allows the determination of the barrier height and bulk resistance in detectors. Changes observed in I - V characteristics and TSC spectra after irradiation are described and a dislocation-net model of radiation-damaged devices is proposed. The deep level and trap spectra were compared in initial and irradiated crystals from different suppliers. A comparison of recently published data of SI-GaAs before and after irradiation by different ionising radiation has been performed and radiation-induced defects and microinhomogeneities have been analysed. Electric field effects in the I - V characteristic quasi-saturation region have been investigated and a model of free carrier lifetime thermal quenching is proposed. The influence of an electric field on light absorption in EL2 centres has been investigated at different temperatures.

Micro-inhomogeneity effects and radiation damage in semi-insulating GaAs radiation detectors

Thermally-stimulated current (TSC) measurements and a detailed analysis of current-voltage (I-V) characteristics have been made on semi-insulating GaAs (SI-GaAs) Schottky diode particle detectors, fabricated on substrates from several suppliers, before and after irradiation with 24 GeV protons and 300 MeV pions. The analysis of I-V characteristics allows the determination of the barrier height and bulk resistance in detectors. Changes observed in I-V characteristics and TSC spectra after irradiation are described and a dislocation-net model of radiation-damaged devices is proposed.