Using the mathematical modeling of a displacement cascade in two wide-gap semiconductors based on gallium, gallium oxide (Ga 2 O 3 ), and gallium nitride (GaN), the features of the generation of Frenkel pairs during the scattering of protons with energies of 8 and 15 MeV are considered. The number of displacements created not only by primary knocked-out atoms, but also by recoil atoms generated in displacement cascades is calculated for the first time. Calculations show that under the proton irradiation of Ga 2 O 3 , for example, the fraction of vacancies in the oxygen sublattice created directly by protons is only 12%. The remaining 88% are created by recoil atoms in cascade processes. For the gallium sublattice, these fractions are 25 and 75%, respectively. Therefore, the processes of compensating the conductivity of GaN and Ga 2 O 3 observed under proton irradiation will be determined by deep centers created not by primary knocked-out atoms, but by recoil atoms formed in displacement cascades. A comparison with experimental data is made, and the fraction of Frenkel pairs dissociating during irradiation is estimated.

The effect of the electron-irradiation temperature on radiation-defect formation in silicon carbide is studied for the first time. Commercial high-voltage 4H-SiC Schottky diodes are studied. Irradiation is carried out by electrons with an energy of 0.9 MeV at temperatures of 20°C and 200°C. The spectra of radiation-induced defects are measured using nonstationary capacitance spectroscopy. It is established that with an increase in the temperature of irradiated silicon carbide, not only the number of introduced radiation defects decreases, but also their spectrum changes. If cold irradiation leads to the formation of six deep traps, then hot irradiation leads to the formation of only three traps: Z1/Z2 (0.68 eV), EH5 (1.08 eV), and EH6/EH7 (1.58 eV). During hot irradiation the number of induced radiation defects also sharply decreases, which leads to a decrease in the rate of removal of charge carriers (compensation of semiconductor conductivity) by almost four times: from 0.25 to 0.065 cm–1. It is noted that nonlinear effects in radiation-defect formation are observed in silicon carbide. At a fixed dose of irradiation of silicon carbide by electrons, the number of introduced radiation defects depends on the electron-flux density (dose-accumulation time).

For the first time, a comparative study of the effect of electron and proton irradiation at a temperature of 20–500°C on the characteristics of semiconductor devices based on silicon carbide, i.e., commercial high-voltage 4H-SiC Schottky diodes, is carried out. The diodes are irradiated with 15-MeV protons and 0.9‑MeV electrons. It is found that the most sensitive parameter, which determines the radiation resistance of devices, is the base resistance, which monotonically increases with the radiation dose D. It is shown that, under low-temperature (“cold”) irradiation, the efficiency of compensation of a semiconductor by proton irradiation is about 400 times higher than the efficiency of electron irradiation. Under “hot” (high temperature) irradiation, the radiation resistance of diodes is several times higher than the resistance of diodes under “cold” irradiation. The rate of formation of deep centers in the upper half of the band gap of silicon carbide decreased with increasing irradiation temperature.

The effect of low-temperature annealing on the capacity–voltage and current–voltage characteristics of silicon-carbide-based semiconductor devices irradiated with 0.9-MeV electrons and 25-MeV protons are studied. Commercial high-voltage (a blocking voltage of 1700 V) integrated 4H-SiC Schottky diodes are used. It is established for the first time that, for both types of irradiation used, not only well-known thermally stable Z1/Z2 and EH6/7 radiation defects compensating the electrical conductivity of n-SiC, but also a second group of radiation defects also creating deep levels in the forbidden band of the semiconductor, but annealed at relatively low (400°С) temperatures are introduced into n-SiC.

The kinetics of the formation of radiation-induced defects in silicon and silicon carbide as a function of the absorbed energy is analyzed. The dependence of the concentration of conduction electrons n-Si and n-SiC on the irradiation dose is studied experimentally under conditions of irradiation with electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. The advantages and disadvantages of using the integral flux (fluence) and absorbed energy as kinetic parameters are discussed. It is established in the performed studies that the visual representation of the kinetics of radiation-induced defect formation as a function of the fluence of irradiating particles is clearer for tabulating the requirements imposed to equipment stability under suitable conditions. To study the physical processes underlying the formation of radiation-induced defects in semiconductors, it is more convenient to use the dependences of the effects observed under radiation exposure as functions of the absorbed energy.

The formation of radiation defects in the silicon-carbide sublattice under irradiation with 15-MeV protons and 0.9-MeV electron is analyzed. Numerical simulation is carried out, and histograms of the distribution of the energy transferred to carbon recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. Single isolated Frenkel pairs with closely located components are produced in the low-energy range. The recoil atom energy is sufficient to produce a displacement cascade in the other range. As the energy of primary knocked-out atoms increases, the average distance between genetically related Frenkel pairs increases, and as a consequence, the fraction of pairs that do not recombine under irradiation increases. The recombination radius of the Frenkel pair in the carbon sublattice is estimated.

Mathematical simulation of the cascade of displacements in SiC is used to consider the specific features of Frenkel-pair generation upon the scattering of 8- and 15-MeV protons. The distribution histograms of energies acquired not only by primary knocked-out atoms, but also by recoil atoms generated in displacement cascades, are calculated. An analysis of the histograms considers two energy ranges. In the first range of “low” energies, the spontaneous recombination of genetically related Frenkel pairs is dominant. Recoil atoms in the second range have a higher energy, which enables these atoms to leave the spontaneousrecombination zone and dissociate into isolated components. The compensation of lightly doped n- and p-4H-SiC samples grown by gas-phase epitaxy is experimentally studied under irradiation with 8- and 15-MeV protons. The carrier removal rates are measured. The calculated and experimental data are compared and estimates are obtained for the size of the spontaneous-recombination zone.

AbstractMathematical simulation of the cascade of displacements in SiC is used to consider the specific features of Frenkel-pair generation upon the scattering of 8- and 15-MeV protons. The distribution histograms of energies acquired not only by primary knocked-out atoms, but also by recoil atoms generated in displacement cascades, are calculated. An analysis of the histograms considers two energy ranges. In the first range of “low” energies, the spontaneous recombination of genetically related Frenkel pairs is dominant. Recoil atoms in the second range have a higher energy, which enables these atoms to leave the spontaneousrecombination zone and dissociate into isolated components. The compensation of lightly doped n - and p -4 H -SiC samples grown by gas-phase epitaxy is experimentally studied under irradiation with 8- and 15-MeV protons. The carrier removal rates are measured. The calculated and experimental data are compared and estimates are obtained for the size of the spontaneous-recombination zone.

The processes of the compensation of n -type conductivity in germanium irradiated with 15-MeV protons are investigated. Irradiation results in a considerable reduction in the density of shallow donor states of Group-V atoms. The rate of removal of shallow donor states due to the interaction between impurity atoms and radiation-induced intrinsic point defects is ~215 cm –1 . The majority of secondary defects produced under proton irradiation are electrically neutral in an n -type material. Radiation-induced acceptors are of little importance in this case. Numerical modeling is performed, and the distribution of the energy transferred to recoil atoms is obtained. Two energy intervals are considered in the analysis of distribution histograms. At low energies, individual Frenkel pairs with closely spaced components are produced. The energy of recoil atoms in the second energy region is sufficient to induce a displacement cascade. Nanoscopic regions with high densities of intrinsic point defects and their complexes with dopant atoms are formed in such cascades. A model of the generation of intrinsic defects in germanium under proton irradiation is discussed.

The electrical characteristics of epitaxial layers of n-4H-SiC (CVD) irradiated with 0.9 and 3.5MeV electrons are studied. It is shown that the donor removal rate becomes nearly four times higher as the energy of impinging electrons increases by a factor of 4, although the formation cross section of primary radiation defects (Frenkel pairs in the carbon sublattice) responsible for conductivity compensation of the material is almost energy independent in this range. It is assumed that the reason for the observed differences is the influence exerted by primary knocked-out atoms. First, cascade processes start to manifest themselves with increasing energy of primary knocked-out atoms. Second, the average distance between genetically related Frenkel pairs grows, and, as a consequence, the fraction of defects that do not recombine under irradiation becomes larger. The recombination radius of Frenkel pairs in the carbon sublattice is estimated and the possible charge state of the recombining components is assessed.

Проведено исследование электрофизических характеристик эпитаксиальных слоев n-4H-SiC (CVD) при его облучении электронами с энергиями 0.9 и 3.5 МэВ. Показано, что скорость удаления доноров увеличивается почти в 4 раза с ростом энергии бомбардирующих электронов в 4 раза, хотя сечение образования первичных радиационных дефектов (пар Френкеля в подрешетке углерода), ответственных за компенсацию проводимости материала, в этом диапазоне практически не зависит от энергии. Предположено, что причиной наблюдаемых различий является влияние первично выбитых атомов. Во-первых, с ростом энергии первично выбитых атомов начинают сказываться каскадные процессы. Во-вторых, увеличивается среднее расстояние между генетически родственными парами Френкеля и как следствие увеличивается доля не рекомбинирующих при облучении дефектов. Проведены оценки радиуса рекомбинации пары Френкеля в подрешетке углерода и возможного зарядового состояния рекомбинирующих компонент. DOI: 10.21883/FTP.2017.03.44199.8399

The formation of radiation defects in Si under 1–10-MeV proton bombardment is analyzed. Numerical simulation is carried out, and histograms of the distribution of the energy transferred to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. Single Frenkel pairs with closely located components are produced in the first range (small energies). Recoil atoms of the second range have an energy sufficient for the production of a displacement cascade. As a result, nanoscale regions with high densities of vacancies and different types of their complexes appear. In addition, as the energy of the primary knocked-out atoms increases, the average distance between genetically related Frenkel pairs increases, and, as a consequence, the fraction of pairs that are not recombined under bombardment increases.

A comparative analysis of the formation of radiation-induced defects in semiconductors (silicon and silicon carbide are used as examples) under bombardment with electrons with energies of 0.9 MeV or higher is carried out. Experimental values of the rate of charge-carrier removal at electron energies of 0.9 MeV are less by an order of magnitude than at higher electron energies (6–9 MeV). The formation cross section for primary radiation defects (Frenkel pairs) in this range is almost energy-independent. It is suggested that the reason for this difference is the influence of the energy of primary knocked-out atoms. As the energy of these atoms increases, first, the average distance between genetically related Frenkel pairs increases, and, as a consequence, the fraction of pairs that are not recombined under bombardment increases. Second, the possibility of forming new, more complex, secondary radiation effects appears as the energy of the primary knocked-out atoms increases.

Проведен сравнительный анализ образования радиационных дефектов в полупроводниках (на примере кремния и карбида кремния) при облучении электронами с энергией 0.9 МэВ и с большими энергиями. Экспериментальные значения скорости удаления носителей заряда при энергии электронов 0.9 МэВ почти на порядок меньше, чем при использовании электронов большей энергии (6–9 МэВ). Сечение образования первичных радиационных дефектов (пар Френкеля) в этом диапазоне практически не зависит от энергии. Предположено, что причиной различий является влияние энергии первично выбитых атомов. С повышением энергии этих атомов, во-первых, увеличивается среднее расстояние между генетически родственными парами Френкеля и, как следствие, увеличивается доля не рекомбинирующих при облучении пар. Во-вторых, с ростом энергии первично выбитых атомов появляется возможность формирования новых, более сложных, вторичных радиационных дефектов.

The dose dependences of the effect of deep semiconductor-conductivity compensation under bombardment with electrons is studied. It is discovered that the linear dependences are characteristic for SiC and GaAs, and the strictly nonlinear dependence is typical of Si. Calculations are carried out, and it is shown that the character of the dose dependence is determined by the compensation mechanism. A model explaining the difference between the characters of the dependences for different semiconductors is proposed.