Materials Science Forum Vols. 600-603

Abstract: The formation of dots by CVD in the hetero-system SiC-Si was studied in the two possible ways : Si dots on SiC substrate and SiC dots on Si substrate. The substrates underwent special surface treatment to reveal a network of parallel steps before deposition of the dots. In the Si on SiC case, the dots density on the 8°off 4H-SiC substrate varied in the range 107 – 7x108 cm-2 and mainly depends on the SiH4 flux and the deposition time. The Si dots are in majority aligned along the step edges of the substrate. In the other hetero-system, only propane was introduced in the reactor to performed a localised carbonisation of the Si(111) 1.5°off substrate. The SiC dots obtained at 1200°C have similar density the Si ones but with smaller size.

Abstract: In this work, the effects of the diameter and morphology on the electronic band structure of hydrogenated cubic silicon carbide (b-SiC) nanowires is studied by using a semiempirical sp3s* tight-binding (TB) approach applied to the supercell model, where the Si- and C-dangling bonds on the surface are passivated by hydrogen atoms. Moreover, TB results (for the bulk) are compared with density functional calculations in the local density approximation. The results show that though surface morphology modifies the band gap, the change is more systematic with the thickness variation. As expected, hydrogen saturation induces a broadening of the band gap energy because of the quantum confinement effect.

Abstract: 3C-SiC is a promising material for high power and high-speed electronic devices as well as in sensors operating at high temperatures or hostile environments. For these reasons, we solved self-consistently the Poisson equation within the quantum Non Equilibrium Green Function Formalism (NEGF) in order to model and compare 3C-SiC and Si nanowire (NW) Field Effect Transistors (FETs) operating in ballistic regime (at room temperature 300 K). As a general conclusion of our calculations, Si and SiC NW FETs have almost the same electrical behavior: they depict the same subthreshold slope and have similar on currents [ION/IOFF (SiC)~81 % ION/IOFF (Si) in case of 4 nm NW cross section side].

Abstract: Crystalline recovery mechanism in the activation annealing process of Al implanted 4H-SiC crystals were experimentally investigated. Annealing temperature and annealing time dependence of acceptor activation and activated hole’s behavior were examined. Poly-type recovery from the implantation induced lattice disordering during the annealing was investigated. The existence of meta-stable crystalline states for acceptor activation, and related scattering centers due to annealing is reported To achieve 100% acceptor activation and to reduce strain after ion implantation, annealing at 2000°C for 10 min. was required.

Abstract: We perform a dynamical simulation of the SiO2/4H-SiC C-face interface oxidation process at 2500K using first-principles molecular dynamics based on plane waves, supercells, and the projector-augmented wave method. The slab model is used for the simulation. Oxygen molecules are dissociated in the SiO2 layers or by Si atoms at the SiO2 interface. The O atoms of the O2 molecule oxidize the C atoms at the SiC interface and form Si-C-O or CO2-C complexes. COx (x=1 or 2) molecules are desorbed from these complexes by thermal motion. COx molecules diffuse in the SiO2 layers when they do not react with dangling bonds. COx molecule formed during C-face oxidation more easily diffuse than those formed during Si-face oxidation in the interface region.

Abstract: The reliability of thermal oxides grown on n-type 4H-SiC C(000-1) face wafer has been investigated. In order to examine the influence of different oxidation atmospheres and temperatures on the reliability, metal-oxide-semiconductor capacitors were manufactured and the different oxides were characterized by C-V measurements and constant-current-stress. The N2O-oxides show the smallest flat band voltage shift compared to the ideal C-V curve and so the lowest number of effective oxide charges. They reveal also the lowest density of interface states in comparison to the other oxides grown on the C(000-1) face, but it is still higher than the best oxides on the Si(000-1) face. Higher oxidation temperatures result in smaller flat band voltage shifts and lower interface state densities. Time to breakdown measurements show that the charge-to-breakdown value of 63% cumulative failure for the N2O-oxide on the C(000-1) face is more than one order of magnitude higher than the highest values measured on the Si(000-1) face. Therefore it can be concluded that a smaller density of interface states results in a higher reliability of the oxide.

Abstract: In the present work, we systematically studied the effect of the annealing temperature (from 1400 °C to 1650 °C) on the electrical activation of 4H-SiC implanted with multiple energy (from 40 to 550 keV) and medium dose (1×1013 cm-2) Al ions. The evolution of the acceptor (NA) and compensating donor (ND) depth profiles was monitored by the combined use of scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM). We demonstrated that the electrical activation of the implanted layer with increasing annealing temperature is the result of the increase in the acceptor concentration and of the decrease in the ND/NA ratio. Atomic force microscopy (AFM) morphological analyses indicated that the surface quality is preserved even after the 1650 °C annealing process.

Abstract: We demonstrate a Dual-Pearson approach to model ion-implanted Al concentration profiles in 4H-SiC for high-precision design of high-voltage power devices. Based on the Monte Carlo simulated data for 35-400 keV implantation, we determine the nine Dual-Pearson parameters and confirm precise reproduction of profiles of 1015-1021 cm-3 Al with sufficient smoothness. This leads to a direct incorporation of implanted Al profiles into a device simulator. The influence of dose and energy on channeling is also discussed from the view point of implantation-induced disorder in 4H-SiC.

Abstract: Defect formation during the ion-implantation/annealing process in 4H-SiC epilayers is investigated by X-ray topography, KOH etching analysis and transmission electron microscopy. Nitrogen and phosphorus ions are implanted in the 4H-SiC epilayers and then activation annealing is performed at 1670 °C. Linearly arrayed or clustered extended defects are found to be formed during the implantation/annealing process by comparing X-ray topography images taken before and after the process. It is confirmed that the defect arrays are formed underneath a shallow groove on the surface and consist of a high density of basal-plane Shockley-type stacking faults.

Abstract: Cross-sectional CL measurements have been performed on the cleaved surface of the Al-ion implanted 4H-SiC. The strong L1 luminescence that originates from the DI defect has been observed even in the deep region (~10 μm) where implanted ions do not penetrate. In the implanted layer, CL results show that high-density non-radiative defects remain even after activation annealing. Generation of the DI defect in the deep region is presumably attributed to the diffusion of point defects from the implanted layer.