Materials Science Forum Vols. 615-617

Abstract: The effect of a cycle "introduction of defects – annealing – introduction of defects" on the SiC properties has been studied to know the degradation of characteristics of p-n- nuclear radiation detectors. The irradiation with 8 МeV protons at fluences of about 3×1014 сm-2 was used. The annealing was carried out in two stages one-hour at temperatures of 600 and 700 °С. Nuclear spectrometric techniques with 5.8 MeV -particles were employed to test the detectors. The charge collection efficiency and features of the amplitude spectrum were determined to study the capture of charge carriers by radiation-induced defects. Measurements were made in the temperature range of 20–250 °С. It is shown that at 250 °С there is a decrease in the carriers capture. The form of the amplitude spectrum essentially improves. The first irradiation and the subsequent annealing do not change significantly the radiation hardness of SiC. During the second irradiation the effective concentration of the introduced centers is 1.3 times higher. This result may be due to the high total fluence of protons, 6×1014 cm-2.

Abstract: The achievement of nuclear detectors in Silicon Carbide imposes severe constraints on the electronic quality and thickness of the material due to the relatively high value of the energy required to generate an electron-hole pair (7.8 eV) in this material compared to the value for Si (3.6 eV). In this work, 4H-SiC charged particle detectors were realised using epitaxial layers of n-type doping as active region. The thickness of the epilayer is always below 80 μm with a net doping concentration in the range of 8 x 1013 to 1016 cm-3. These properties allowed the fabrication of Schottky diodes that operate well as radiation detectors. At low doping concentration, the epilayer is totally depleted at quite low reverse bias (≈ 50 V), thereby obtaining the maximum active volume.

Abstract: We investigated the energy spectra in p+n 6H-SiC diodes by a wide variety of charged particles with energies up to several hundred MeV. Though Pulse Height Defect (PHD) was detected when the samples were irradiated with high energy heavy ions (322MeV-Kr and 454MeV-Xe), linearity between pulse height (peak channel) and ion energy up to 150MeV was observed.

Abstract: In this work, avalanche photodiodes (APDs) were fabricated using a-plane 6H- and 4H-SiC materials to investigate their electrical and optical properties. Temperature dependence of avalanche breakdown was measured. The diode structures were fabricated with positive angle beveling and oxide passivation to ensure a uniform breakdown across the device area. Despite the apparent presence of micro-plasmas, we observed that the breakdown voltage of a-plane 6H-SiC APDs increased with temperature suggesting a positive temperature coefficient.

Abstract: We report on the fabrication and testing of SiC p-i-n avalanche photodiodes. APDs of 0.25 mm2 area on a-plane (1120) 6H-SiC as well as off-axis Si face 6H and 4H-SiC were successfully fabricated. A beveled mesa was used as edge termination. Recessed windows were formed using reactive ion etching to enhance low-wavelength UV performance. We performed current-voltage tests with and without UV illumination to determine dark current, photocurrent, and gain on selected devices. Dark current was less than 1 pA at 0.5Vbr on multiple devices. Quantum efficiency of 40% or greater was observed for all orientations and polytypes.

Abstract: In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.

Abstract: 4H-SiC single photon avalanche diodes are reported. A separate absorption and multiplication non-reach through device structure was optimized for operation in Geiger mode. An estimated dark current at a gain of 1000 was ranging between 0.4 pA (0.75 nA/cm2) and 20nA (38 A/cm2) on devices with an effective mesa diameter of 260 m. The electron beam induced current technique was used to image defects in the active region of studied devices. Increased reverse bias leakage current and increased Geiger mode dark count probability were correlated with the presence of large number of defects. Single photon detection efficiencies of up to 11% were measured at a wavelength of 266 nm in Geiger mode.

Abstract: The photo-response of 3C-SiC pn homojunction photodiodes was measured at high temperature up to 673K. At 473K, the response is hardly different from that at the room temperature. At 573K and 673K, the peak is red shift and lowering comparing that of 298K. The response increases on the long-wavelength region of the profile because of an increase in optical absorption coefficient on increase in temperature. Responsivities at various temperatures were calculated using one-dimensional diffusion model. The calculated profiles of response are qualitatively in agreement with the experimental results except for that of 473K.

Abstract: The development of silicon carbide technologies has allowed for the development of sensors and electronics to measure the changes in a variety of hostile environments. A problem has been identified with reliable and efficient ways to power such sensors in these hostile environments. It is likely to be impractical to run power cables to these sensors and battery power has a finite lifetime. Recent research has demonstrated many energy scavenging techniques but to date none have been developed with a view of operation in hostile environments. To investigate the power density achievable from a SiC based energy scavenging device a SiC pin diode was exposed to both broad spectrum light form a tungsten halogen bulb and a 255 nm UV source. IV and CV measurements were used to determine the structural properties and photovoltaic response of the device, dark saturation current, induced photo current and the fill factor. We present the characteristics and maximum power density of these devices at temperatures between 300 K and 600 K. We demonstrate that the maximum power density achievable decreases with temperature. This is mostly due to the reduction in the built in potential from the pn junction, and the reduction of the generated photocurrent.

Abstract: In the long run, regenerative energy sources represent the most important alternatives to fossil fuels. In general, they are characterized by decentralized logistics and supply capabilities due to ihnerent lower energetic densitiy per are, when compared with the fossil counterparts. As a result, the increased use of regenerative energy sources will require decentralized structures for energy supply, consumption optimisation and regional balancing between supply and demand. Both, the more efficient utilization of fossil energy sources and the utilization of regenerative energy sources, lead to increasingly decentralized supply structures and can be understood as being both complementary and convergent in relation to each other. Most of the converter units for utilization of decentralized energy resources (DER) use power electronics for the AC power conditioning with grid quality. The current paper shows market perspectives of DER applications and the impact of SiC on these application.