Materials Science Forum Vols. 615-617

Abstract: The photoluminescence (PL) from the I 1 centre is observed in p-, n-type as well as in compensated samples, using above band gap excitation. The PL from I 1 in the two polytypes 4H and 6H is very similar, the difference being the position of the main peak, in 4H 1.1521 eV and 1.1057 eV in 6H. We here suggest I-1 to be Mo related based on intentional doping, SIMS results and comparison with earlier reports of Mo in SiC using magnetic resonance techniques. From PL measurements, we analyze the electron structure of the defect, and suggest it be the neutral Mo (4d2) residing on a Si site, the luminescence coming from the transition between the 3A2 multiplet of the first excited electronic configuration and the ground state 3A2.

Abstract: 1 MeV ion implantations of 4H SiC have been performed to various doses with ion probes of 5 µm diameter. Defect introduction has been studied by microscopic photoluminescence.

Abstract: An attempt is made, in the light of recent developments in the identification of intrinsic defects in 4H SiC, to account for differences that have been reported after electron-irradiation of different samples and to discuss the progression of defects that is observed on annealing. The emphasis is placed on internal stress in the material and on defects involving carbon anti-sites and silicon vacancies because they are readily detected by photoluminescence.

Abstract: We describe the potential use of scanning probe microscopy (SPM) to image at nanoscale the charge transport in conductive layers, through dielectrics and barriers and in general for mapping of physical properties in wide band gap materials, processing and devices. Measurements through conductive layers are described discussing the limits and potentialities. Carrier profiling by SPM is presented and critically discussed as a complex method, crossing information from several techniques, to extract more insights related to carrier distribution.

Abstract: 4H Silicon Carbide (4H-SiC) has a great potential for low-loss power devices due to its superior electrical properties. However, the increase in demand for the power devices requires high quality SiC substrates and epitaxial layers. Mercury probe Capacitance Voltage (Hg CV) measurement is a well known procedure to characterize epi layers grown on SiC substrates, due to its non-destructive technique. However, careful calibration of the tool is very important for repeatable and accurate measurements. Here we present very close repeatability of Hg CV within 2.4% (standard deviation 0.7%), between different Solid State Measurements (SSM) setups compared with Ni Schottky (NiS) CV. In addition to growing uniformly doped epi layers, high surface quality of the epi layer is also needed for improved device performance. Improved process conditions resulted in a smooth epi with a surface roughness Ra 1.2 nm for a 6 µm thick epi layer. Molten Potassium Hydroxide (KOH) etching analysis also revealed a significant correlation between the surface roughness and epi defects.

Abstract: Available data on Schottky barrier heights on silicon and carbon rich faces of 4H-SiC have been carefully analyzed to investigate the mechanism of barrier formation on these surfaces. As in case of 3C and 6H-SiC, the barrier heights depend strongly upon method of surface preparation with a considerable scatter in the barrier height for a given metal-semiconductor system. However, for each metal the barrier height depends on the metal work function and strong pinning of the Fermi level has not been observed. The slopes of the linear relation between the barrier heights and metal work functions varies over a wide range from 0.2 to about 0.75 indicating that the density of interface states depends strongly on the method of surface preparation. By a careful examination of the data on barrier heights we could identify a set of nearly ideal interfaces in which the barrier heights vary linearly with metal work function approaching almost to the Schottky limit. The density of interface states for these interfaces is estimated to lie between 4.671012 to 2.631012 states/ cm2 eV on the silicon rich surface and about three times higher on the carbon rich faces. We also observed that on these ideal interfaces the density of interface states was almost independent of metal indicating that the metal induced gap states (MIGS) play no role in determining the barrier heights in metal-4H-SiC Schottky barriers.

Abstract: Forward current-voltage characteristics of non-ideal Ti / 4H-SiC Schottky barriers with ideality factor n = 1.1 - 1.2 have been analyzed. The non-ideality is considered as a result of formation of a thin intermediate dielectric layer between the deposited titanium layer and 4H-SiC. Using experimental current-voltage characteristics, the electro-physical characteristics of Ti contacts such as the energy barrier height, the thickness of the intermediate layer and the energy distribution of the interface trap density are determined.

Abstract: Electron channeling contrast imaging (ECCI) has been utilized to evaluate the surface morphology and crystalline quality of 3C-SiC films grown by chemical vapor deposition (CVD) on (100) and (111) Si substrates. ECCI in this study was performed using an electron backscatter diffraction (EBSD) system equipped with forescatter diode detectors and mounted inside a commercial scanning electron microscope (SEM). This nondestructive method permits direct dislocation imaging through local fluctuations in forescattered electron yield attributable to lattice strain. Coordinated ECCI, SEM, and EBSD analysis of film surfaces allowed correlations between film orientation, surface morphology, and dislocation behavior. Evidence of lateral dislocations parallel to <110> directions and atomic step pinning by dislocations was observed.

Abstract: The three-layer heterostructure formed by the two domains of the cubical 3C-SiC polytype and hexagonal NH-SiC (N = 4, 6, 8) layer is considered. The Poisson equation with the account of spontaneous polarization for the hexagonal component has been solved with the assumption that the resulting electric field can be treated as a sum of contact and polarization field components. The analytical expression for the value of the dimensionless band-bending potentials on the interfaces is found. It is demonstrated that the account of the spontaneous polarization leads to the asymmetry of the energy diagram, which results in an inequality of the quantum wells located at the interfaces. The possibility of the indirect electronic transition between the states of these quantum wells is considered.

Abstract: This paper describes the growth and characterisation of Si/SiC heterojunction structures. Heterojunction structures are of interest for low on-resistance diodes and as potential solutions to fabricating SiC MOS devices with lower interface state densities. The formation of the Si/SiC heterojunction using Chemical Vapour Deposition (CVD), Molecular Beam Epitaxy (MBE), Electron Beam Evaporation under UHV conditions (EBE-UHV) and Layer Transfer (LT) are reported. The physical nature of Si/SiC structures has been investigated using scanning electron microscopy (SEM). Results of electrical characterisation of the Si/SiC heterojunctions, are also reported. Finally, thermal oxidation of a Si / SiC heterojunction structures has been performed. The C(V) characteristics of the resulting oxides are compared to conventional thermal oxides on SiC.