Materials Science Forum Vols. 645-648

Abstract: In this work, we have studied I-V characteristics of Al breakdown in 6H-, 4H- and 15R-SiC in electrical field. As a result there obtained the next original data: 1) decreasing dependence of breakdown field due to the concentration increase in the range of Na – Nd = 5x1017–1019 cm-3; 2) absence of low temperature breakdown when Na - Nd< 1017 cm-3; 3) increasing of breakdown field while temperature declines from 77K to 4.2K; 4) at 300K the breakdown field decreases and the breakdown takes place in samples with the absence of low temperature breakdown; 5) gigantic enhancement of breakdown field at F||C. 6) the theoretical analysis based on the theory of a zero radius potential supports the probability of breakdown field enhancement at F||C.

Abstract: We report on the electrical characterization of high-purity semi-insulating 4H-SiC after annealing at temperatures between room temperature and 1700 oC by current-mode deep level transient spectroscopy (I-DLTS). I-V and Hall-effect measurements revealed that the investigated substrates possess p-type conductivity. Four deep levels were detected by I-DLTS with activation energies in the 0.15-1.29 eV range. We studied their thermal stability as well as their stability with respect to light illumination.

Abstract: We produce amorphous terbium doped wide bandgap semiconductor thin films of the pseudobinary compound (SiC)1 x(AlN)x by rf triple magnetron sputtering. Cathodoluminescence measurements performed at samples having different compositions x show pronounced intra 4f shell transition peaks of the trivalent terbium. Thermal activation of the terbium emission by isochronal annealing of the films leads to a strong increase in emission intensity.

Abstract: Two electrical measurement techniques are frequently employed for the characteri- zation of traps at the SiO2/SiC interface: the thermal dielectric relaxation current (TDRC) and the conductance method (CM). When plotting Dit as a function of the energy position Eit in the bandgap both techniques reveal comparable results for deep interface traps (EC􀀀Eit > 0:3 eV). For shallower traps, CM always shows a strong increase of Dit which originates from near interface traps (NIT). TDRC provides a contradictory result, namely a slight decrease of Dit. In this paper, we show that the position of NITs in the oxide close to the interface is responsible for the invisibility of these traps in TDRC spectra. We further show that NITs become detectable by the TDRC method by using a discharging voltage Vdis close to the accumulation regime. However, due to the Shockley-Ramo-Theorem the contribution of NITs to the Dit in TDRC spectra is strongly suppressed and can be increased by using thin oxides.

Abstract: Thermally stimulated current (TSC) measurements on epitaxial and implanted 4H-SiC MOS capacitors are presented. The effect of gamma ray irradiation on the TSC spectra of epitaxial 4H-SiC MOSCAP devices is discussed. On non-irradiated samples, two TSC peaks are observed near 55 K and 80 K. Due to the generated oxide charge during irradiation, the 80 K emission split into two constituent peaks. These have been attributed to hole traps and Al acceptors.

Abstract: We have comparatively characterized the electrical characteristics of 4H-SiC and 2H-GaN MOS capacitors and FETs. While progressive refinement of gate oxide processes, notably with NO anneal, has resulted in better threshold voltage control, reduced subthreshold slope and higher field-effect mobility for 4H-SiC MOSFETs, we have recently reported more superior MOS parameters for 2H-GaN MOSFETs. In addition, we have performed MOS-gated Hall measurements to extract the intrinsic carrier concentration and MOS mobility, indicating that both less channel electron trapping and scattering take place in 2H-GaN MOSFETs.

Abstract: We explain the role of nitrogen in simultaneously increasing the inversion channel mobility and reducing the threshold voltage of SiC MOSFET. A variety of computational techniques have been used to compute the atomic scale configuration of a nitridated SiC/SiO2 interface, and the corresponding change in Fermi level, inversion channel mobility, and threshold voltage. X-ray photoelectron spectroscopy (XPS) has been used to investigate the SiC/SiO2 interface to determine the nitrogen concentrations and chemical bonding. We elucidate the physics behind improved channel mobility due to NO anneal and demonstrate that the trade-off between threshold voltage and inversion channel mobility can be correlated to the extent of nitridation.

Abstract: We perform dynamical simulations of dry oxidation and NO annealing of the SiO2/4H-SiC C-face interface at 1500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. In the dry oxidation simulation, O atoms oxidize not only the C atoms at the SiC interface but also second-atomic-layer Si atoms in the SiC layer. Bilayer oxidation occurs in the oxidation process. The formation of C clusters that grow in the c-axis direction is observed. In the simulation of NO annealing, N atoms passivate interface C atoms. The density of N atoms saturates, then N atoms desorb as N2 molecules. CN molecules are formed by the abstraction of C atoms by the N atoms, and the CN molecules readily react at the interface. The formation of a Si3N structure is also observed.

Abstract: The authors investigated the effect of preannealing on N-/Al-coimplanted and over-oxidized Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs). The preannealing process causes a decrease of the Hall mobility and the effective mobility, and an increase of the interface state density. Secondary ion mass spectroscopy (SIMS) measurements revealed that the N concentration at the SiO2/SiC interface in preannealed samples is lower than in not-preannealed samples, which might be the reason for in the increase of the interface state density. In MOSFETs without preannealing, more N atoms are piled up at the SiO2/SiC interface, leading to the lower interface state density and higher mobility.

Abstract: In this paper the electrical and structural characteristics of n-MOSFETs fabricated on 4H SiC with a process based on nitrogen (N) implantation in the channel region before the growth of the gate oxide are reported for low (5x1018 cm-3) and high (6x1019 cm-3) N concentration at the SiO2/SiC interface. The electron mobility and the free carrier concentration in the MOSFET channel were evaluated by Hall effect measurement. The MOSFETs with the higher N concentration had the best electrical characteristics in terms of threshold voltage and field effect mobility, in spite of a lowering of the electron mobility in the channel. The latter is a negative drawback of the fabrication process that probably can be ascribed to an incomplete recovery of the implantation damage or to a high density of interstitial N atoms present in the channel region. In fact, the MOSFETs with the superior electrical performances were fabricated with the higher N+ dose and the shorter thermal oxidation time. However, no evidence of extended defects, clusters or nano-particles in SiC at the interface with the gate oxide was found in every SiC MOSFETs devices observed by electron transmission microscopy