Papers by Keyword: Radiation Defect

Abstract: To understand the kinetics of changes in the majority current carriers Hall mobility temperature-dependency (in the temperature range of 77–300 K) in n- and p-type silicon crystals irradiated with high doses of high-energy particles during isochronous annealing, there are investigated P-doped n-Si samples irradiated with 25 MeV protons with dose of 8.1·10¹² cm^–2 at flux density of 1.5∙10¹¹ cm^–2·s^–1 and B-doped p-Si samples irradiated with 8 MeV electrons with dose of 1.0·10¹⁵ cm^–2 at flux density of 5.0·10¹² cm^–2·s^–1 at room temperature. Their isochronous annealing is performed in the temperature range of 80–500°C. The oscillatory character of the change in the majority current carriers Hall mobility in process of isochronous annealing of irradiated silicon samples is explained by the formation of disordered regions and the changes in degree of screening of their electric field potential barriers depending on charge states of nonequilibrium vacancies induced by irradiation.

Abstract: EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100^OC temperature range. Three new paramagnetic defects named Ky6, Ky7 and Ky8 have been revealed. Based on the present results, these defects have been tentatively attributed to the negatively charged carbon vacancy-carbon antisite pair, negatively charged divacancy and neutral carbon <100> split interstitial, respectively. Furthermore, the finding of practically isotropic hyperfine splitting for EPR lines of the T6 center confirms its assignment as a carbon vacancy-interstitial pair.

Abstract: Photoluminescence (PL) spectroscopy has been used to characterize neutron-irradiated cubic silicon carbide crystals. The effects of thermal annealing (600-1100^OC) on the PL bands have been studied. Several PL bands consisting of a sharp line and its phonon replicas have been observed in the 9-80 K temperature range. Certain of them like the D₁ spectrum doublet with 1.975 eV and 1.977 eV zero-phonon lines (ZPL) at 9 K and the L2 spectrum with ZPL at 1.121 eV were reported previously for ion-implanted and electron irradiated 3C-SiC crystals, respectively. Besides, some new bands with ZPL at 2.027, 1.594, 0.989 and 0.844 eV and a broad band at 1.360 eV have been found. A correlation of PL and EPR spectra intensities of these neutron-irradiated and annealed cubic SiC crystals is briefly discussed.

Abstract: Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

Abstract: The irradiation with 0.9 MeV electrons and with 8 MeV and 15 MeV protons were performed for studying radiation defects. Proton scattering in a silicon carbide film has been numerically simulated. Distribution histograms of the energy imparted to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. In the first range of “low” energies, individual Frenkel pairs with closely spaced components are created. In the second range, recoil atoms have energies sufficient for generating a cascade of displacements. This gives rise to microscopic regions with high density of vacancies and vacancy complexes of various kinds.

Abstract: The recovery of shallow donor states of the atoms of phosphorus in n-FZ-Si:P material irradiated at the room temperature with 15 MeV protons was studied in the course of isochronal annealing. This process was investigated by the positron annihilation lifetime (PAL) spectroscopy and by low-temperature electrical measurements. The positron traps of a vacancy type manifesting themselves as deep donors have been revealed. These defects begin to anneal at ~ 593 K– 613 K; roughly estimated activation energy of the process is Ea ≈ 0.59 eV under the first order of reaction. The results suggest the involvement, at least, of one vacancy and the impurity atom of phosphorus in the microstructure of the deep donor.

Abstract: Results of a DLTS study on the deep-level centers in the copper-contaminated electron-irradiated FZ-Si are presented. Copper was diffused from the Cu-contaminated surface into previously irradiated samples at 350 K. The most abundant Cu-related complexes formed due to this procedure are the same as in the case of previously studied Cu-diffused Cz-Si.

Abstract: The effect of tin on the formation and temperature transformation of VO centers in Ge upon annealing has been investigated. It was found that the doping of Ge with tin leads to a change of reactions involving oxygen and vacancies and the new defect SnVO appears upon VO annealing. Doping Ge with tin gives rise to a considerable decrease in the formation efficiency of divacancies and VO centers and the latter exist in a very narrow temperatures range. VO2 complexes appear only upon annealing of SnVO centers. The assumption is made that the absorption bands situated at 718.9 and 733.6 cm^-1 belong to the less stable configuration VO₂* and the bands at 731.5 and 771.7 cm^-1 correspond to stable configuration of VO₂ centers.

Abstract: The isotopic effect of hydrogen and deuterium on hydrogenation of radiation defects introduced in n-type float zone and Czochralski silicon by irradiation with high-energy alphas was investigated. Silicon diodes were first irradiated with 2.4 MeV alphas to a fluence of 1x10¹⁰ cm^-2 and then hydrogen or deuterium was introduced by rf plasma treatment at 250°C. Reactions of hydrogen and deuterium with radiation defects were monitored by deep-level transient spectroscopy during subsequent isochronal annealing at temperatures ranging from 100 to 400°C. Results show that hydrogen rf plasma effectively neutralizes majority of vacancy related radiation defects created by alphas in both materials. In contrast with it, neutralization by deuterium plasma is substantially weaker. Disappearing of vacancy related defect levels due to hydrogen (deuterium) treatment is accompanied by introduction of two dominant deep levels at E_C-0.309 eV and E_C-0.365 eV. While hydrogenation significantly accelerates annealing of radiation defects especially in Czochralski material, deuteration has weaker effect and gives rise to new defect levels during annealing.

Abstract: The changes of the positron lifetime and loss/recovery of shallow donor states in n-FZ-Si:P material irradiated at the room temperature with 15 MeV protons have been investigated in the course of isochronal annealing. Thermally stable point radiation defects which begin to anneal at ~ 300 C° – 340 C° have been revealed; they manifest themselves as deep donors. It is argued that these defects involve, at least, more than one vacancy and the impurity atom (s) of phosphorus.