Materials Science Forum Vols. 740-742

Abstract: Our message is oxidation process must be minimized as possible. Many carbon-related defect structures are reported in SiC/SiO2 interface. In this paper, we investigated the effect of oxidation to the defect forming by density functional theory (DFT). In the result, we found carbon defect structure that completely different from in the present report. This defect structure has carbon-carbon single bond with no dangling bond. To see the forming process, compressive strain from inserted oxygen atoms induce the rearrangement of structure and cause C-C defect structure. We can know that this structure is formed with energy gain about 3.8eV. And this C-C defect induces trap state under the conduction bottoms.

Abstract: In this paper, interaction mechanism of hydrogen with GaN metal-insulator-semiconductor (MIS) diodes has been investigated, focusing on the metal/semiconductor interfaces. As a result, the following three points are revealed: First, MIS Pt-SiO2-GaN diodes show a marked improvement in detection sensitivity, suggesting that the device interface plays a critical role in sensing. Second, exposure of the diodes to hydrogen is found to change the conduction mechanisms from Fowler-Nordheim tunneling to Pool-Frenkel emission. Third, interface trap level density of the diodes is found to be reduced by hydrogen exposure even at room temperature. These results support the validity of the hydrogen-induced dipole layer model.

Abstract: Constant-capacitance deep-level-transient spectroscopy (CCDLTS) characterization of traps (or states) in SiO₂/SiC interfaces on the C-face was carried out to clarify the cause of low-channel mobility of SiC MOSFETs. CCDLTS measurements showed that the interface-state density (D_it) near the conduction band of SiO₂/SiC interfaces fabricated using N₂O oxidation was much higher than that of SiO₂/SiC interfaces fabricated using wet oxidation. The high density of interface states near the conduction band is likely to be the main cause of the low mobility of MOSFETs fabricated using N₂O oxidation.

Abstract: Micro-Raman spectroscopy is an excellent non-destructive analysis method, which compensates for disadvantages of KOH method. Raman shift of A1(LO) and E1(TO) band at threading screw dislocation(TSD) were investigated in n-type on/off-axis 4H- and 6H-SiC single crystal wafers by Micro-Raman scattering at room temperature. The results showed that A1(LO) band were shifted toward higher frequency while the E1(TO) band were shifted toward lower frequency on the on-axis wafers. The shifts are caused by increasing electron concentration and lattice disorder near the dislocation core, respectively. In the off-axis wafers, no shifts were observed possibly due to the measurement geometry which does not contain whole dislocation core.

Abstract: The near-SiC-interfaces of annealed Ni/SiC contacts were observed directly by high-resolution transmission electron microscopy (HRTEM). 1 nm native oxide layer was observed in the as-deposited contact interface. The native oxide layer cannot be removed at 650°C through rapid thermal annealing (RTA) and it was completely removed at 1000°C RTA. The residue of native oxide layer resulted in the Schottky characters. High temperature annealing (>950°C) not only removes the oxide layer in the near-SiC-interface, but also forms a well arranged flat Ni2Si/SiC interface, which contribute to the formation of ohmic behavior.

Abstract: Carrier lifetimes in 6H-SiC epilayers were investigated by using numerical simulations and micro-wave photoconductivity decay measurements. The measured carrier lifetimes were significantly increasing with an increased thickness up to 200 μm while it stays almost constant in layers thicker than 200 μm. From a comparison of the simulation and experimental results, we found that if the bulk lifetime in 6H-SiC is around a few microseconds, both the surface recombination and interface recombination influence the carrier lifetime in layers with thickness less than 200 μm while only the surface recombination determines the carrier lifetime in layers with thickness more than 200 μm. In samples with varying thicknesses, a bulk lifetime = 2.93 μs and carrier diffusion coefficient D= 2.87 cm²/s were derived from the linear fitting of reciprocal lifetime vs reciprocal square thickness.

Abstract: Cubic silicon carbide - silicon dioxide core-shell nanowires have been synthesized in a thermal CVD system from carbon monoxide on silicon substrate. Using a non-ionic surfactant during the coating process of the substrate by the catalyst, the uniformity of the catalytic layer was improved, resulting in a more uniform nanowires growth. It is demonstrated that the core diameter is strongly correlated with the precursor concentration.

Abstract: 3C-SiC (n) / Si (p) heterostructures were obtained and investigated in a wide temperature range. It was shown, the main mechanisms of charge transport diffusion and recombination. The properties of silicon substrate were determining the working temperature range of investigated diodes. Therefore the rectifying properties of 3С-SiC(n)/Si(p) diodes were stable only up to 473 K. Two sites with different activation energies were observed on the Jrev(1/T) curves at fixed voltage: 0,32 eV which, characterized states on the SiC/Si interface, Е2 ≈ 0,55 eV which corresponds to the middle of silicon bandgap and defines existence of reverse current generation component.

Abstract: The impact of the thickness of an AlN spacer in AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures on the Hall mobility was investigated in a range of 30 K - 340 K. The AlN spacer has a strong impact on the mobility at temperatures below 150 K. This effect is linked to a reduction of alloy scattering. Optical and scanning electron microscopy revealed hexagonal shaped defects which also have an effect on the mobility. These defects can be avoided by an appropriate adjustment of the AlN layer thickness.

Abstract: In this paper, we characterized MOS devices fabricated on 4H-SiC (0-33-8) face. The interface state density of SiO₂/4H-SiC(0-33-8) was significantly low compared to that of SiO₂/4H-SiC(0001). The field-effect channel mobility obtained from lateral MOSFET (LMOSFET) was 80 cm²/Vs, in spite of a high p-well concentration of 5x10¹⁷ cm^-3 (implantation). The double implanted MOSFET (DMOSFET) fabricated on 4H-SiC(0-33-8) showed a specific on-resistance of 4.0 mΩcm² with a blocking voltage of 890 V.