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Evolution of the microwave-probed photoconductivity transients and of the proton induced luminescence has simultaneously been examined in polycrystalline CdS layers evaporated in vacuum during exposure to a 1.6MeV proton beam. The decrease of the intensity of luminescence peaked at 510 and 709 nm wavelengths and of values of the effective carrier lifetime has been correlated in dependence of proton irradiation fluence. The defect introduction rate has been evaluated by the comparative analysis of the laser and proton beam induced luminescence. The difference of a carrier pair generation mechanism inherent for light and for a proton beam has been revealed. [ABSTRACT FROM AUTHOR]

The electric field distribution and charge drift currents in Si particle detectors are analyzed. Profiling of the injected charge drift current transients has been implemented by varying charge injection position within a cross-sectional boundary of the particle detector. The obtained profiles of the induction current density and duration of the injected charge drift pulses fit well the simulated current variations. Induction current transients have been interpreted by different stages of the bipolar and monopolar drift of the injected carriers. Profiles of the injected charge current transients registered in the non-irradiated and neutron irradiated Si diodes are compared. It has been shown that the mixed regime of the competing processes of drift, recombination, and diffusion appears in the measured current profiles on the irradiated samples. The impact of the avalanche effects can be ignored based on the investigations presented. It has been shown that even a simplified dynamic model enabled us to reproduce the main features of the profiled transients of induced charge drift current. [ABSTRACT FROM AUTHOR]

GaN with intentionally incorporated carbon to create semi-insulating buffer layers shows improved performance in AlGaN/GaN heterojunction field effect transistors. Moreover, various impurities and crystal imperfections of GaN epi-layers determine a rather rich spectrum of deep levels. Thus, spectroscopy of defects is of paramount importance in optimizing GaN-based devices. In this work, pulsed photo-ionization spectroscopy (PPIS) has been applied to trace the prevailing defects and simultaneously monitor variations of carrier lifetime in metal−organic chemical vapor deposition grown GaN epi-layers on Si substrates of various carbon content concentration. A contactless technique for microwave probed photoconductivity has been employed to measure changes in excess carrier density, in order to evaluate variations in carrier lifetime and reveal the type of photo-activation processes. Six PPI spectral steps have been resolved in samples containing either superlattices (SLs) or AlN/AlGaN stress management layers. Three of these centres, namely, and (CNON)0, have been associated with carbon dopants. Other PPIS peaks have been ascribed to Ga vacancies and metal impurities. It has been deduced from analysis of the PPIS peak broadening factor that rather strong electron−phonon coupling is inherent in photo-ionization of carbon related complexes at room temperature. The concentration of separated defects and cross-sections for photon−electron coupling have been determined using calibration measurements of optical transmittance spectra and correlations between microwave probed photoconductivity peak signals and absorption coefficient. [ABSTRACT FROM AUTHOR]

In order to evaluate carrier densities created by 1.6MeV protons and to trace radiation damage of the 2.5 μm thick GaN epi-layers grown by metalorganic chemical vapor deposition technique, a correlation between the photoconductivity transients and the steady-state photoluminescence spectra have been examined. Comparison of luminescence spectra induced by proton beam and by laser pulse enabled us to evaluate the efficiency of a single proton generation being of 1×107 cm-3 per 1.6 MeV proton and 40 carrier pairs per micrometer of layer depth. This result indicates that GaN layers can be an efficient material for detection of particle flows. It has been demonstrated that GaN material can also be a rather efficient scintillating material within several wavelength ranges. [ABSTRACT FROM AUTHOR]

Gallium nitride is a wide-direct-bandgap semiconductor suitable for the creation of modern optoelectronic devices and radiation tolerant detectors. However, formation of dislocations is inevitable in MOCVD GaN materials. Dislocations serve as accumulators of point defects within space charge regions covering cores of dislocations. Space charge regions also may act as local volumes of enhanced non-radiative recombination, deteriorating the photoluminescence efficiency. Surface etching has appeared to be an efficient means to increase the photoluminescence yield from MOCVD GaN materials. This work aimed to improve the scintillation characteristics of MOCVD GaN by a wet etching method. An additional blue photo-luminescence (B-PL) band peaking at 2.7-2.9 eV and related to dislocations was discovered. This B-PL band intensity appeared to be dependent on wet etching exposure. The intensity of the B-PL was considerably enhanced when recorded at rather low temperatures. This finding resembles PL thermal quenching of B-PL centers. The mechanisms of scintillation intensity and spectrum variations were examined by coordinating the complementary photo-ionization and PL spectroscopy techniques. Analysis of dislocation etch pits was additionally performed by scanning techniques, such as confocal and atomic force microscopy. It was proved that this blue luminescence band, which peaked at 2.7-2.9 eV, is related to point defects those decorate dislocation cores. It was shown that the intensity of this blue PL band was increased due to enhancement of light extraction efficiency, dependent on the surface area of either single etch-pit or total etched crystal surface.

Minority carrier traps play an important role in the performance and radiation hardness of the radiation detectors operating in a harsh environment of particle accelerators, such as the up-graded sensors of the high-luminosity hadron collider (HL-HC) at CERN. It is anticipated that the sensors of the upgraded strip tracker will be based on the p -type silicon doped with boron. In this work, minority carrier traps in p -type silicon (Si) and silicon-germanium (Si 1-x Ge x ) alloys induced by 5.5 MeV electron irradiation were investigated by combining various modes of deep-level transient spectroscopy (DLTS) and pulsed technique of barrier evaluation using linearly increasing voltage (BELIV). These investigations were addressed to reveal the dominant radiation defects, the dopant activity transforms under local strain, as well as reactions with interstitial impurities and mechanisms of acceptor removal in p -type silicon (Si) and silicon-germanium (SiGe) alloys, in order to ground technological ways for radiation hardening of the advanced particle detectors. The prevailing defects of interstitial boron-oxygen (B i O i ) and the vacancy-oxygen (VO) complexes, as well as the vacancy clusters, were identified using the values of activation energy reported in the literature. The activation energy shift of the radiation-induced traps with content of Ge was clarified in all the examined types of Si 1-x Ge x (with x = 0-0.05) materials.

In this work, electrically active defects of pristine and 5.5 MeV electron irradiated p -type silicon-germanium (Si 1-x Ge x )-based diodes were examined by combining regular capacitance deep-level transient spectroscopy (C-DLTS) and Laplace DLTS (L-DLTS) techniques. The p -type SiGe alloys with slightly different Ge contents were examined. It was deduced from C-DLTS and L-DLTS spectra that the carbon/oxygen-associated complexes prevailed in the pristine Si 0.949 Ge 0.051 alloys. Irradiation with 5.5 MeV electrons led to a considerable change in the DLT spectrum containing up to seven spectral peaks due to the introduction of radiation defects. These defects were identified using activation energy values reported in the literature. The double interstitial and oxygen complexes and the vacancy, di-vacancy and tri-vacancy ascribed traps were revealed in the irradiated samples. The interstitial carbon and the metastable as well as stable forms of carbon-oxygen (C i O i * and C i O i ) complexes were also identified for the electron-irradiated SiGe alloys. It was found that the unstable form of the carbon-oxygen complex became a stable complex in the irradiated and the subsequently annealed (at 125 °C) SiGe samples. The activation energy shifts in the radiation-induced deep traps to lower values were defined when increasing Ge content in the SiGe alloy.

The particle detector degradation mainly appears through decrease of carrier recombination lifetime and manifestation of carrier trapping effects related to introduction of carrier capture and emission centers. In this work, the carrier trap spectroscopy in Si 1-x Ge x structures, containing either 1 or 5% of Ge, has been performed by combining the microwave probed photoconductivity, pulsed barrier capacitance transients and spectra of steady-state photo-ionization. These characteristics were examined in pristine, 5.5 MeV electron and 1.6 MeV proton irradiated Si and SiGe diodes with n + p structure.

Wide bandgap AlGaN is one of the most promising materials for the fabrication of radiation hard, double-response particle detectors for future collider facilities. However, the formation of defects during growth and fabrication of AlGaN-based devices is unavoidable. Furthermore, radiation defects are formed in detector structures during operation at extreme conditions. In this work, study of evolution of the proton-induced luminescence spectra and short-circuit current has been simultaneously performed during 1.6 MeV proton irradiation. GaN and AlGaN (with various Al concentrations) epi-layers grown by metalorganic chemical vapour deposition technique and Schottky diode structures have been examined. Variations of spectral and electrical parameters could be applied for the remote dosimetry of large hadron fluences., Competing Interests: The authors declare no conflict of interest.

Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μ e = 1000 ± 200 cm²/Vs for electrons, and μ h = 400 ± 80 cm²/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.

The operational characteristics of capacitor-type detectors based on HPHT and CVD diamond have been investigated using perpendicular and parallel injection of carrier domain regimes. Simulations of the drift-diffusion current transients have been implemented by using dynamic models based on Shockley-Ramo's theorem, under injection of localized surface domains and of bulk charge carriers. The bipolar drift-diffusion regimes have been analyzed for the photo-induced bulk domain (packet) of excess carriers. The surface charge formation and polarization effects dependent on detector biasing voltage have been revealed. The screening effects ascribed to surface charge and to dynamics of extraction of the injected bulk excess carrier domain have been separated and explained. The parameters of drift mobility of the electrons μ(e) = 4000 cm2/Vs and holes μ(h) = 3800 cm2/Vs have been evaluated for CVD diamond using the perpendicular profiling of currents. The coefficient of carrier ambipolar diffusion D(a) = 97 cm2/s and the carrier recombination lifetime τ(R,CVD) ≌ 110 ns in CVD diamond were extracted by combining analysis of the transients of the sensor current and the microwave probed photoconductivity. The carrier trapping with inherent lifetime τR,HPHT ≌ 2 ns prevails in HPHT diamond.