Radiation technologies for optimization of Si device parameters and techniques for control of radiation defects

In high energy physics experiments the semiconductor particle detectors of pin structure are commonly employed for tracking of the ionising particles. However, ionising radiation creates defects and consequently affects the parameters of particle detectors. Therefore, it is necessary to characterize irradiated detectors and search for the new approaches on how to suppress or control the degradation process. Measurements of current-voltage, capacitance-voltage characteristics as well as deep level transient spectroscopy, thermally stimulated currents spectroscopy are employed for the characterization of irradiated particle detectors. At high irradiation fluences when defects concentration exceeds that of dopants, a generation current increases and, thus, the above mentioned techniques can not be applied for the correct evaluation of defect parameters. In this work, models describing displacement currents in detectors due to redistribution of electric field determined by variations of external voltage or a moving charge in electric field are discussed. These models were applied for creation of the advanced techniques which allow evaluating of charge transport, trapping and recombination/generation parameters in heavily irradiated detectors after irradiation. These techniques were applied for the spectroscopy of deep levels associated with defects, for cross-sectional scans within layered junction structures as well as for examination of defects evolution during irradiation. In this work, the detail analysis of the results obtained during irradiation and on post-irradiated detectors is presented. High power and high switching speed rectifiers of pin structure are widely employed in electronic circuits. The switching speed of these devices can be manipulated by introducing recombination centres ascribed to Au or Pt doping or by employing radiation technologies. Introduction of recombination centres inevitably leads to the enhancement of forward voltage drop and leakage current, and, thus, to degradation of a device parameters. Therefore, the static and dynamic parameters can be optimized in a compromise way. In this work, study of the optimization of functional parameters of power pin diodes has been performed. The developed technologies, based on irradiations with protons of various energy and fluence, to create layers of the enhanced recombination containing various profiles within a base region of the device, are described in this thesis

Radiacinės Si prietaisų parametrų optimizavimo ir radiacinių defektų kontrolės technologijos

In high energy physics experiments the semiconductor particle detectors of pin structure are commonly employed for tracking of the ionising particles. However, ionising radiation creates defects and consequently affects the parameters of particle detectors. Therefore, it is necessary to characterize irradiated detectors and search for the new approaches on how to suppress or control the degradation process. Measurements of current-voltage, capacitance-voltage characteristics as well as deep level transient spectroscopy, thermally stimulated currents spectroscopy are employed for the characterization of irradiated particle detectors. At high irradiation fluences when defects concentration exceeds that of dopants, a generation current increases and, thus, the above mentioned techniques can not be applied for the correct evaluation of defect parameters. In this work, models describing displacement currents in detectors due to redistribution of electric field determined by variations of external voltage or a moving charge in electric field are discussed. These models were applied for creation of the advanced techniques which allow evaluating of charge transport, trapping and recombination/generation parameters in heavily irradiated detectors after irradiation. These techniques were applied for the spectroscopy of deep levels associated with defects, for cross-sectional scans within layered junction structures as well as for examination of defects evolution during irradiation. In this work, the detail analysis of the results obtained during irradiation and on post-irradiated detectors is presented. High power and high switching speed rectifiers of pin structure are widely employed in electronic circuits. The switching speed of these devices can be manipulated by introducing recombination centres ascribed to Au or Pt doping or by employing radiation technologies. Introduction of recombination centres inevitably leads to the enhancement of forward voltage drop and leakage current, and, thus, to degradation of a device parameters. Therefore, the static and dynamic parameters can be optimized in a compromise way. In this work, study of the optimization of functional parameters of power pin diodes has been performed. The developed technologies, based on irradiations with protons of various energy and fluence, to create layers of the enhanced recombination containing various profiles within a base region of the device, are described in this thesis

Profiling of current transients in capacitor type diamond sensors

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 μe = 4000 cm2/Vs and holes μh = 3800 cm2/Vs have been evaluated for CVD diamond using the perpendicular profiling of currents. The coefficient of carrier ambipolar diffusion Da = 97 cm2/s and the carrier recombination lifetime τR,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

5.5 MeV electron irradiation-induced transformation of minority carrier traps in p-type Si and Si1−xGex alloys /

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 (Si1−xGex) 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 (BiOi) 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 Si1−xGex (with x= 0–0.05) materials

Simulations of operation dynamics of different type GaN particle sensors

The operation dynamics of the capacitor-type and PIN diode type detectors based on GaN have been simulated using the dynamic and drift-diffusion models. The drift-diffusion current simulations have been implemented by employing the software package Synopsys TCAD Sentaurus. The monopolar and bipolar drift regimes have been analyzed by using dynamic models based on the Shockley-Ramo theorem. The carrier multiplication processes determined by impact ionization have been considered in order to compensate carrier lifetime reduction due to introduction of radiation defects into GaN detector material

Study of charge carrier transport in GaN sensors

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 μe = 1000 ± 200 cm2/Vs for electrons, and μh = 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

Study of radiation-induced defects in p-type Si1-xGex diodes before and after annealing

In this work, electrically active defects of pristine and 5.5 MeV electron irradiated p-type silicon–germanium (Si1−xGex)-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 Si0.949Ge0.051 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 (CiOi* and CiOi) 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 allo

Transient electrical and optical characteristics of electron and proton irradiated SiGe detectors

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 Si1-xGex 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

Evolution of scintillation and electrical characteristics of AlGaN double-response sensors during proton irradiation

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

Pulsed photo-ionization spectroscopy of traps in as-grown and neutron irradiated ammonothermally synthesized GaN

Abstract GaN-based structures are promising for production of radiation detectors and high-voltage high-frequency devices. Particle detectors made of GaN are beneficial as devices simultaneously generating of the optical and electrical signals. Photon-electron coupling cross-section is a parameter which relates radiation absorption and emission characteristics. On the other hand, photon-electron coupling cross-section together with photo-ionization energy are fingerprints of deep centres in material. In this work, the wafer fragments of the GaN grown by ammonothermal (AT) technology are studied to reveal the dominant defects introduced by growth procedures and reactor neutron irradiations in a wide range, 1012–1016 cm−2, of fluences. Several defects in the as-grown and irradiated material have been revealed by using the pulsed photo-ionization spectroscopy (PPIS) technique. The PPIS measurements were performed by combining femtosecond (40 fs) and nanosecond (4 ns) laser pulses emitted by optical parametric oscillators (OPO) to clarify the role of electron-phonon coupling. Variations of the operational characteristics of the tentative sensors, made of the AT GaN doped with Mg and Mn, under radiation damage by reactor neutrons have been considered