The mechanism of structure transformation in Cr/4H-SiC UV photodetectors, which is responsible for the cyclic gettering of radiation defects, under repeated proton irradiation, is proposed in this work.

The mechanism of structure transformation in Cr/4H–SiC UV photo detectors, which is responsi-ble for the cyclic gettering of radiation defects, under repeated proton irradiation, is proposed in this work.

Forward and reverse current-voltage characteristics (I-V) of Cr/SiC(4H) Schottky diodes (SDs) manufactured using the same technology based on a single weakly-doped (similar to 4.10(14) cm(-3)) epilayer are investigated. SDs are close to ideal, but a significant spread of I-V and excess current which sometimes unstable were found, unrelated to the difference in the area of the SDs. Investigation in the temperature range 20-210 degrees C revealed the annealing effect and allowed to estimate the potential barrier height of different diodes before and after annealing. It is suggested that the main diode is shunted by a parasitic diode, which determines forward I-V in the region of I-V exponential dependence.

Abstract. The results of the effect of irradiation with Ar ions on the structural, electrophysical and optical characteristics of the ultraviolet Cr/4H-SiC photodetectors in the spectral range of 200−400 nm are presented. After a single irradiation with 53MeV Ar ions with a fluence of 1 · 1010 cm−2, the quantum efficiency of the photodetectors practically remained at the level of the initial samples due to the "gettering effect“ of simple radiation defects by cluster formations. The observed effect promoted a decrease in the number of simple radiation defects of the vacancy type, an increase in the lifetime of current carriers, and, as a consequence, unchanged values of the photoconductivity of Cr/4H-SiC photodetectors. After repeated irradiation of the photodetectors with Ar ions with a total fluence of 2 · 1010 cm−2, the decay of clusters was observed, the formation of a significant number of simple defect centers, which led to a decrease in the lifetime of current carriers and, as a consequence, to a decrease in photoconductivity of Cr/4H-SiC photodetectors.

The results of the effect of irradiation with Ar ions on the structural, electrophysical, and optical characteristics of ultraviolet Cr/4H-SiC photodetectors in the spectral range 200 to 400 nm are presented. After a single irradiation with Ar ions with an energy of 53 MeV with a fluence of 1 × 1010 cm–2 the values of the quantum efficiency of photodetectors practically remain at the level of the initial samples due to the “gettering effect” of simple radiation defects by cluster formations. This effect contributes to a decrease in the number of simple radiation defects of the vacancy type, an increase in the lifetime of current carriers, and, as a result, unchanged values of the photoconductivity of Cr/4H-SiC photodetectors. After the repeated irradiation of photodetectors with Ar ions with a total fluence of 2 × 1010 cm–2 the decay of clusters and the formation of a significant number of simple defect centers are observed, which lead to a decrease in the lifetime of the current carriers and photoconductivity of Cr/4H-SiC detectors.

Abstract. The results of the effect of irradiation with Ar ions on the structural, electrophysical and optical characteristics of the ultraviolet Cr/4H-SiC photodetectors in the spectral range of 200−400 nm are presented. After a single irradiation with 53MeV Ar ions with a fluence of 1 · 1010 cm−2, the quantum efficiency of the photodetectors practically remained at the level of the initial samples due to the "gettering effect“ of simple radiation defects by cluster formations. The observed effect promoted a decrease in the number of simple radiation defects of the vacancy type, an increase in the lifetime of current carriers, and, as a consequence, unchanged values of the photoconductivity of Cr/4H-SiC photodetectors. After repeated irradiation of the photodetectors with Ar ions with a total fluence of 2 · 1010 cm−2, the decay of clusters was observed, the formation of a significant number of simple defect centers, which led to a decrease in the lifetime of current carriers and, as a consequence, to a decrease in photoconductivity of Cr/4H-SiC photodetectors.

Forward and reverse current-voltage (IV) characteristics of Cr-SiC (4H) Schottky diodes based on epitaxial layers with doping (1-3)· 10 15 cm -3 were studied in the temperature range of 300-550 K. It is shown that in many cases the IV characteristics are close to ideal, but a significant spread of the forward IV characteristics of diodes manufactured in the same way on the same epitaxial layer was found, probably due to the spread of the Schottky barrier heights reaching 0.3 eV. Heating of the diode, as well as packaging, can also change the Schottky barrier height. An alternative explanation suggests the presence of a powerful shunt.

Abstract The paper presents the results of a study of the effect of irradiation with heavy Ar ions on the structural and optical characteristics of 4H-SiC. It has been shown that as a result of already single irradiation with Ar ions with an energy of 53 MeV with a fluence of 1٠1010 cm-2, at least 2 powerful local regions with negative deformation prevail in the structure of silicon carbide. Along with this, a region with positive deformation is also observed in the structure. The formation of localized clusters with negative and positive deformations, along with the undisturbed matrix, is accompanied by the formation of linear type defects that partially relieve stresses in the structure. It is assumed that the resulting complex defect structure upon irradiation with Ar ions provides the effect of gettering of point defects and leads to the quantum efficiency of 4H-SiC UV photodetectors at the level of the initial samples.

The results of investigations of initial n-4H–SiC structures by various methods are presented. The structures represent a highly doped n+ substrate with epitaxial layers 5 μm thick grown by chemical vapor deposition (CVD). The concentration of uncompensated donors in the epitaxial layer is in the range of Nd – Na = (1–50) × 1014 cm–3. Using the results of X-ray diffraction analysis, it is found that, in order to obtain efficient 4H–SiC ultraviolet photodetectors, it is desirable to have structures of epitaxial layers in which the effect of point-defect gettering, leading to an increase in the lifetime of charge carriers and in the values of quantum efficiency, is observed. The photosensitivity of the investigated samples significantly depends on the degree of imperfection of the CVD epitaxial layer, which results in a change in the lifetime of charge carriers and, as a consequence, in a change in the quantum efficiency of 4H–SiC ultraviolet photodetectors.

The influence exerted by the carrier concentration in the range (1–50) × 1014 cm–3 in n-4H-SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 1012 cm–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4H-SiC devices at elevated temperatures.

The effect of irradiation by protons with an energy of 15 MeV with fluences of (1-40)٠1012 cm-2 on the spectral characteristics of UV 4H-SiC photodetectors was considered. Photodiodes with Schottky barriers were formed by thermal vacuum sputtering with a thickness of 20 nm and a diameter of 8 mm on 4H-SiC structures with CVD epitaxial layers with a concentration of uncompensated donors Nd-Na=(1-4)٠1014 cm-3 grown on n+-4H-SiC substrates. UV photodetectors withstand irradiation by protons with a fluences of 4٠1013 cm-2 with a photosensitivity improvement due to the gettering of simple radiation defects by localized cluster and amorphous areas, and partial structural improvement of the irradiated material. Irradiation of photodetectors by 15 MeV protons with a fluence of 4٠1012 cm-2 at a temperature of 2000 C led to an increase in quantum efficiency compared to samples irradiated in similar modes at 250 C due to an additional defective rearrangement.

The results of a study into the effect of irradiation with heavy Ar ions on the structural and optical characteristics of 4H-SiC are presented. It is shown that even upon single-time irradiation with 53-MeV Ar ions at a fluence of 1 × 1010 cm–2 there are at least two powerful local regions with negative deformation dominant in the structure of silicon carbide. Also, a region with positive deformation is observed in the structure. The formation of localized clusters with negative and positive deformations along with the undisturbed matrix gives rise to linear-type defects that partially relieve stresses in the structure. It is assumed that, upon irradiation with Ar ions, the resulting complex defect structure provides the effect of point-defect gettering and leads to a quantum efficiency of 4H-SiC UV photodetectors that is comparable with that of the initial samples.

Представлены результаты исследования различными методиками исходных структур n-4H-SiC, представляющих высоколегированную n+-подложку с выращенным химическим осаждением из газовой фазы эпитаксиальным слоем толщиной 5 мкм. Концентрация носителей заряда в эпитаксиальном слое в диапазоне Nd-Na=(1-50)·1014 см-3. Привлекая результаты рентгеноструктурного анализа, было установлено, что для получения эффективных 4H-SiC ультрафиолетовых фотоприемников желательно иметь структуры эпитаксиальных слоев, в которых наблюдается эффект геттерирования точечных дефектов, что приводит к росту времени жизни носителей заряда и увеличению значений квантовой эффективности. Фоточувствительность исследованных образцов значительно зависит от степени дефектности в CVD эпитаксиальном слое, приводящей к изменению времени жизни носителей заряда и, как следствие, к изменению квантовой эффективности 4H-SiC ультрафиолетовых фотоприемников. Ключевые слова: карбид кремния, рентгеноструктурный анализ, эффект геттерирования, квантовая эффективность.

Abstract The influence exerted by the carrier concentration in the range (1–50) × 10^14 cm^–3 in n -4 H -SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 10^12 cm^–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4 H -SiC devices at elevated temperatures.

Comparative studies of the structural, electrophysical properties and spectral sensitivity of 4 H -SiC photodetectors of ultraviolet radiation in the spectral range of 200-400 nm were carried out before and after electron irradiations. Photodetectors with Cr Schottky barriers with thickness of 20 nm and 8 mm diameter were formed on n -4 H -SiC CVD epitaxial layers with a thickness of 5 μm and concentration N d -N a = (1-4) х10 14 cm -3 . Cr/4 H -SiC photodiodes were irradiated by electrons at 0.9 MeV energy with doses (0.2-1) x10 16 cm -2 .

AbstractFor the first time, comprehensive comparative investigations of ultraviolet photodetectors with Cr Schottky barriers formed on 4 H -SiC epitaxial layers are carried out by the X-ray and optical methods before and after irradiation with 15-MeV protons with fluences in the range of (1–4) × 10^12 cm^–2. When increasing the fluence of proton irradiation, the formation of localized regions with negative deformation is observed along with the unperturbed silicon-carbide matrix. Agreement between the X-ray and optical studies is obtained, which makes it possible to explain the features of the spectral changes in the photosensitivity of detectors in the range of 200–400 nm with an increase in the fluence of proton irradiation. The ultraviolet Cr/4 H -SiC photodetectors withstand irradiation by 15-MeV protons with a fluence of 4 × 10^12 cm^–2 virtually without any changes in the photosensitivity due to the gettering of simple defects by cluster and amorphous formations, which lead to partial structural improvement of the irradiated material.

For the first time, comprehensive comparative investigations of ultraviolet photodetectors with Cr Schottky barriers formed on 4 H -SiC epitaxial layers are carried out by the X-ray and optical methods before and after irradiation with 15-MeV protons with fluences in the range of (1–4) × 10 12 cm –2 . When increasing the fluence of proton irradiation, the formation of localized regions with negative deformation is observed along with the unperturbed silicon-carbide matrix. Agreement between the X-ray and optical studies is obtained, which makes it possible to explain the features of the spectral changes in the photosensitivity of detectors in the range of 200–400 nm with an increase in the fluence of proton irradiation. The ultraviolet Cr/4 H -SiC photodetectors withstand irradiation by 15-MeV protons with a fluence of 4 × 10 12 cm –2 virtually without any changes in the photosensitivity due to the gettering of simple defects by cluster and amorphous formations, which lead to partial structural improvement of the irradiated material.

Terahertz electroluminescence of unipolar n⁺⁺-n⁻-n⁺ SiC structures at helium temperatures and I-V characteristics of bipolar n⁺⁺-π-n⁺ SiC structures with natural superlattices at 300~K at strong electrical fields are studied. The properties of the THz electroluminescence and I-V characteristics testify that these phenomena due to Bloch oscillations.

This work examines the electrical and radiometric characteristics of a photodiode based on a 4H-SiC semiconductor material with a semitransparent Cr Schottky barrier of about 7 nm thickness. The device had a photo-sensitive area 10 mm in diameter. The spectral responsivity was determined in the wavelength range from 40 nm to 400 nm, thus particularly extending the characterization into the vacuum- and extreme ultraviolet spectral ranges. The photodiode showed a maximum quantum efficiency of 50% at 253 nm with a relative uniformity of 4% in the photosensitivity over its surface. The linearity of the photoresponse was measured at wavelengths of 70 nm and 265 nm for incident radiant powers from 2 nW to 800 nW, and no significant deviation from linearity was found. Regarding its electrical characteristics, the photodiode showed less than 10(-13) A dark current at a reverse voltage of 10 V. (C) 2018 Optical Society of America

Purpose: Purpose of the study was to assess psycho-somatic condition in fitness club members including depending on age, cultural diversity and duration of fitness training. Subjects:Russian Group included 148 novice, aged from 18 to 63 years and 36 long-term (i.e., involved into fitness training for 2 years) aged from 24 to 66 years female members of the urban fitness facility.Canadian Group included 100 females, aged from 19 to 71 years.The study groups were additionally stratified into younger (<50 years) and older (>50 years) subgroups.Methods: All participants were interviewed; Anthropometric measures and Aerobic Sub-maximal Stress-test were performed.Russian Group persons were additionally screened using Visual Analogue Scale, Hospital Anxiety and Depression Scale, E.Heim's coping inventory.Results: Female members of the diverse urban fitness facilities could not be positioned as mainly sound persons due to presumable arterial hypertension, locomotive problems; predominantly increased weight; prevalence of anxiety, depression. Conclusion:The obtained data confirm the necessity of accurately designed psycho-somatic assessment of female fitness-clients.