Materials Science Forum Vols. 556-557

Abstract: We fabricate pn-junction diode on p-type 4H-SiC(0001), in which n-type region is formed by N ion implantation at room temperature (total dose: 2.4 x 1015 /cm2, thickness: 300 nm) and subsequently annealed for 5 min using electron bombardment annealing system (EBAS). The root-mean-square (RMS) surface roughness and sheet resistance (Rs) for N ion implanted region, annealed at 1900 oC is estimated to be 0.7 nm and 940 4/sq., respectively. The alloyed Ni ohmic contact to N ion implanted layer, annealed at 1900 oC, shows the contact resistance (Rc) of 8.3 x 10-5 4cm2. The forward drop voltage at 100 A/cm2 and on-resistance of mesa-type pn junction diode is estimated to be 3.1 V and 1.3x10-2 4cm2. The reverse bias leakage current of that is 2.2 x 10-5 A/cm2 at 100 V. It is demonstrated that EBAS is able to apply for the fabrication of pn-junction diode.

Abstract: 4H-SiC p-i-n diodes were fabricated on epitaxial layers grown by Sublimation Epitaxy in Vacuum (SEV) and were evaluated for microwave power switching applications. Full electrical characterization (C-V, DC I-Vs, reverse recovery characteristics, low and high power microwave testing) has been performed. The results showed that SEV-grown SiC material is suitable for bipolar device fabrication. A doping higher than 1019 cm-3 for the p-type contact layer and lower than 1016 cm-3 for the n-type base layer is necessary to demonstrate microwave p-i-n diodes with similar performance as the ones fabricated on commercially available CVD-grown material.

Abstract: Zener diodes are widely used in electrical barriers to protect equipment operating in a potentially explosive atmosphere. Although normally not conducting, the zeners must have a high power rating so that their junction temperature meets safety factors when shunting the maximum fuse current. This often requires two or three lower voltage commercial zeners connected in series. Silicon carbide diodes have much higher thermal conductivity and maximum allowed junction temperature, so it should be possible to use one SiC zener in the place of two or three commercial diodes and/or allow use of higher fuse ratings. Low voltage SiC Zener diodes were fabricated and tested to evaluate potential benefits of their application as a component of intrinsically safe barriers. The diodes demonstrated mixed avalanche-tunnel breakdown at reverse bias voltages of 23 V with positive temperature coefficients of breakdown voltages of about 0.4 mV/°C. The diodes with mesa area of 4×10-4cm2 had maximum DC Zener current of 1.2 A and were capable of operating at ambient temperatures up to 500°C.

Abstract: The detector structures based on Al ion-implanted p+-n junctions in 4H-SiC have been manufactured and tested at temperatures up to 170oC by α-particles with energies of 3.9 and 5.5 MeV. Structural peculiarities of thin Al high dose ion implanted layers before and after short high temperature activation annealing were studied by combination of Rutherford back scattering/channeling spectrometry and cross-sectional transmission electron microscopy. The detector structures fabricated on this thin ion implanted p+-n junctions operated in the temperature range of 16-170 oC with reproducible stable spectrometric characteristics. The charge collection efficiency and the energy resolution of detectors improved with rising temperature up to 170 oC, that was obtained in SiC detectors for the first time.

Abstract: The fabrication of high sensitive diodes array is very attractive for spectroscopic and astronomical UV imaging applications, particularly when visible light rejection is required. Wide band gap materials are excellent candidates for UV “visible blind” detection. In this paper, we demonstrate an array of Schottky UV-diodes on 4H-SiC with a single pixel area of about 1.44 mm2 and a total area of about 29 mm2. The Schottky photodiodes are based on the pinch-off surface effect, the front electrode being an interdigit Ni2Si contact that allows the direct light exposure of the optically active device area. For the proposed array, the optically active area is about the 48 % of total area. The single pixel dark current was below 0.1 nA up to –50 V and a fabrication yield of about 90 % was observed. The external quantum efficiency of the proposed array exhibits a peak of 45 % at the 289 nm wavelength and a visible rejection ratio > 4 ×103.

Abstract: Silicon Carbide has proven its relevance for various MEMS and sensors devices applications. This paper presents the fabrication and the first test results of 3C-SiC electrostatic resonators actuated by applying a combination of AC and DC voltages. The recipe used for the fabrication has taken the advantage of the starting material, 3C-SiC grown on Si, which allows us to use the Si substrate as sacrificial layer to release the structures. Resonators have been fabricated by a two-step process, combining RIE ICP etching with HF wet etching. Resonators have been successfully electrostatically actuated in air-ambient condition. The resonance frequencies were clearly identified, although capacitive current created by actuation was not detected.

Abstract: Avalanche photodiodes (APDs) based on 4H-SiC are excellent candidates to replace PMTs in the UV, particularly for harsh environment applications. Here, we report on dark current analysis of 4H-SiC APDs with separate absorption and multiplication regions. Detailed analysis of the leakage current as a function of device size showed that for a given device design, the bulk leakage component is dominant at U>600V, while surface leakage is dominant at U<600V. Electron beam induced current was also used to establish a correlation between leakage current and major types of defects in the substrate. There were two types of dislocations that could be easily distinguished in the images, including threading (spots) and basal plane (comet-like) dislocations. Using image processing software, densities of threading dislocations as well as basal plane dislocations were obtained and correlated with leakage currents of the corresponding APDs. The results suggest a strong effect of threading dislocations on dark current. Densities of basal plane dislocations were very similar in all devices tested suggesting that a role of basal plane dislocations was not dominant in leakage current of the APDs.

Abstract: SiC is a biocompatible material and a candidate as a transducer for biosensors. Here we have investigated the possibility to functionalize SiC with biomolecules. We have also processed very simple devices and performed electrical characterization. Double polished SiC samples with a C-face substrate and Si-face low doped epilayer have been functionalized on both sides. The SiC was first treated by HF in order to remove the native oxide, partly successful on the Si-face side but probably not on the C-face side. MPTMS, 3-mercaptopropyl trimethoxysilane, was chosen as the biomolecule since it has both a silanol group to be used as an anchoring group to the substrate and a thiol group available for further linking possibilities. The functionalization was evaluated by XPS, contact angle experiments, AFM and electrical measurements. The MPTMS molecules attached with the thiol (or sulphur containing) group pointing out from the surface on both faces of the SiC. Interesting differences between the two faces are however revealed by the analysis.

Abstract: The charge collection efficiency (ССЕ) of SiC-detectors preliminarily irradiated with 8 MeV protons at a fluence of 1014 cm-2 has been studied. Nuclear spectrometric techniques with 5.4 MeV α-particles were employed to test the detectors. The concentration of primarily created defects was estimated to be 4×1016 cm-3. A strong compensation of SiC was observed, which allowed connection of the structure in the forward mode. The experimental data obtained were processed using a simple two-parameter model of signal formation. The model makes it possible to separate the contributions of electrons and holes to the ССЕ. An additional irradiation at a fluence of 2×1014 cm-2 reduced the ССЕ value by a factor of 2 and gave rise to polarization. The latter indicates that radiation-induced centers are not only actively involved in carrier localization (with a decrease in the lifetime), but also in transformation of the electric field within the detector.

Abstract: Due to research results have already been published