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AlN thin films grown on different face sapphire substrates by metalorganic chemical vapor deposition were studied comprehensively by a variety of techniques including high resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS) and theoretical calculations. Our results showed that substrate orientation has a drastic effect on the initial growth of AlN. The AlN films showed dominant semipolar (101) orientation but with slightly weaker individual features. Optical reflectance measurements confirmed that AlN films grown on different surface orientation sapphire substrates at the same time possessed different film thicknesses. It was found that the surface orientation also has a major influence on the dislocation density, crystallite size, and surface oxygen incorporation. Raman line width exhibited good correlation with XPS measurements. The combined analyses led to a better understanding of the variation in the quality of the AlN films grown on different faces of sapphires.

Comprehensive experimental and theoretical studies are reported to assess the vibrational and structural properties of 3C-SiC/Si (001) epilayers grown by chemical vapor deposition in a vertical reactor configuration. While the phonon features are evaluated using high resolution infrared reflectance (IRR) and Raman scattering spectroscopy (RSS) – the local inter-atomic structure is appraised by synchrotron radiation extended x-ray absorption fine structure (SR-EXAFS) method. Unlike others, our RSS results in the near backscattering geometry revealed markedly indistinctive longitudinal- and transverse-optical phonons in 3C-SiC epifilms of thickness d

This paper reports on the dependence of cycling or endurance in flash memory with the stress induced by low-pressure chemical vapor deposition (LPCVD) process. The deposited 12.5nm tetraethyl orthosilicate (TEOS) layer served as sacrificial oxide during source/drain (S/D) implantation, which was then subsequently removed. However, this deposited TEOS layer has been found to induce a stress on the channel which affects the flash memory cycling or endurance performance.

The synthesis of nano-crystalline Mg–Mn ferrites by a solution combustion method using citric acid and ammonia was investigated by varying the pH of the precursor solution, which played an important role in controlling the morphology of the synthesized powders. The phase formation, microstructure and electromagnetic properties were studied using X-ray diffraction, scanning electron microscopy, impedance analyzer and vibrating sample magnetometer. Single phase pure spinel Mg–Mn ferrite powders were obtained for all the samples at different pH (

Directing the morphological evolution of one-dimensional materials in order to tune their properties for a variety of practical applications in optical sensing and solar cells is an ongoing effort. Here, we establish a systematic method for exerting control over the morphology of nanowires (NWs) grown via a vapour–solid–solid (VSS) process from different metal catalysts. We use germanium, a technologically important material, to demonstrate how catalysts influence the axial growth rate of a crystalline core against the lateral vapour deposition of an amorphous shell which in turn deforms the NWs into straight, tapered or spiral geometries due to interfacial stress. Finite element method (FEM) and molecular dynamic (MD) simulations are further utilized to confirm the proposed mechanism of deformation in crystalline–amorphous core–shell NWs.

Magnesium silicates (MgxSiOy) and in particular forsterite (Mg2SiO4) owing to their low thermal expansion mismatch with metals are promising materials for bioactive coating of implants. Here, we report the electrophoretic deposition (EPD) of forsterite onto titanium substrates using different precursors. Unlike bulk samples which achieve full stoichiometry only beyond 1400 °C, non-stoichiometric magnesium silicate rapidly decomposes into magnesium oxide nanowires during sintering. Elemental mapping and X-ray diffraction suggest that oxygen diffusion followed by ion exchange near the substrate leads to formation of an interfacial Ti5Si3 layer. Pre-annealed forsterite powder on the other hand shows a comparatively lower diffusion rate. Overall, magnesium silicate coatings do not exhibit thermally induced microcracks upon sintering as opposed to calcium phosphate bioceramics which are currently in use.

Solid state thermal diffusion is not a common method of impurity doping in silicon carbide (SiC) device fabrication due to the extremely high temperatures required for such a process to occur. We have recently reported that solid state impurity doping by thermal diffusion in SiC is possible if there is a parallel mechanism, such as oxidation or silicidation that creates silicon or carbon vacancies, which then allows dopant impurities to diffuse into these vacancies. This paper describes the experimental procedures by which oxidation and silicidation can be used to generate vacancies and enhance impurity doping at temperatures below 1400 oC‎

FTIR, Visible and UV Raman scattering, as well as synchrotron radiation X-ray absorption, in combination, have been employed to investigate a series of CVD grown 3C-SiC/Si (100). Significant results on the optical and atomic bonding properties are obtained from these comparative studies.

An electroless nickel film contains 5-14% by weight of phosphorus. Because of the presence of such a high concentration of phosphorus, electroless nickel can be a useful and convenient source of phosphorus dopant in the fabrication of n-type ohmic contacts for SiC. This paper describes the successful deposition of a Ni:P layer on 4H-SiC through electroless nickel plating followed by a discussion of the results of surface science and electrical measurements. Specific contact resistivity on lightly-doped samples with carrier concentration of 2.5 ´ 1016 cm-3 has been found to be about 4.8 ´ 10-6 Ωcm2 without any need for ion implantation. This metallization technique is especially useful in broad area ohmic contact formation on the back of n-type SiC substrate.

Synchrotron radiation extended X-ray absorption fine structure and Raman scattering were used to characterize a series of 3C-SiC films grown on Si (100) by chemical vapor deposition. EXAFS can probe the physical and chemical structure of matters at an atomic scale and Raman parameters such as intensity, width, peak frequency and polarization provide fruitful information on the crystal quality and properties of these film materials.

The low temperature diffusion of Boron in bulk SiC crystals is investigated and simplified model of such diffusion is presented. The method of UV stimulated etching by aqueous solution of KOH is proposed and some experimental data on influence of defects on quality of prepared p-n junctions are presented.

The characteristics of boron diffusion in 3C-SiC at low temperature have been measured using spreading resistance technique and electroluminescence spectroscopy. The coefficient of boron diffusion in the temperature range of 1150 –1250°С has been found to be about 5.5 x 10-11–5.0 x 10-10 cm2/sec and the activation energy of boron diffusion was determined to be about 0.9 –1.15 eV. Electroluminescence spectra of 3C-SiC p-n junction structures showed peaks at 750 and 630 nm due to growth defects and carbon-silicon divacancies respectively.

Thermal oxides on the Ga-face of low defect density bulk gallium nitride (GaN) were controllably produced under varying conditions and subsequently analyzed. The thermal oxidation was performed in a dry oxygen atmosphere at different temperatures and different oxidation times. Each oxide layer was identified as the monoclinic β-Ga2O3 by a θ–2θ X-ray diffraction (XRD) scan. Complementary Auger electron spectroscopy (AES) and high-resolution X-ray photoelectron spectroscopy (XPS) were also performed to study the chemical and electronic states of the oxide. The surfaces of the as-grown oxide and the GaN surfaces (after oxide removal) were studied using scanning electron microscopy (SEM). The roughness of both surfaces was found to increase with increasing oxidation temperature. Schottky diodes were fabricated on the GaN surfaces after oxide removal to further examine the surface quality. An excess reverse leakage current was found for Schottky diodes fabricated on GaN surfaces that were oxidized at 950 °C or 1000 °C, indicating possible surface decomposition at these two temperatures. The characteristics of wet and dry etching of the gallium oxide layer were also investigated. Finally, metal–oxide–semiconductor (MOS) capacitors were fabricated using thermally oxidized bulk GaN substrates. Current–voltage (I–V) measurements showed a low reverse current of 1.5 pA at −10 V. The oxide breakdown field was determined to be 0.65 MV/cm. Capacitance–voltage (C–V) measurements displayed a deep depletion feature, and the interface trap density near the conduction band was estimated to be in the low 1011 eV−1 cm−2 range.

Vertical Schottky rectifiers have been fabricated on a free-standing n-GaN substrate. Circular Pt Schottky contacts with different diameters (50 μm, 150 μm and 300 μm) were prepared on the Ga-face and full backside ohmic contact was prepared on the N-face by using Ti/Al. The electron concentration of the substrate was as low as ∼7 × 1015 cm−3. Without epitaxial layer and edge termination scheme, the reverse breakdown voltages (VB) as high as 630 V and 600 V were achieved for 50 μm and 150 μm diameter rectifiers, respectively. For larger diameter (300 μm) rectifiers, VB dropped to 260 V. The forward turn-on voltage (VF) for the 50 μm diameter rectifiers was 1.2 V at the current density of 100 A/cm2, and the on-state resistance (Ron) was 2.2 mΩ cm2, producing a figure-of-merit (VB)2/Ron of 180 MW cm−2. At 10 V bias, forward currents of 0.5 A and 0.8 A were obtained for 150 μm and 300 μm diameter rectifiers, respectively. The devices exhibited an ultrafast reverse recovery characteristics, with the reverse recovery time shorter than 20 ns.

Silicon carbide (SiC) field plate terminated Schottky diodes using silicon dioxide (Si02) dielectric experience high electric field in the insulator and premature dielectric breakdown, attributed to the lower dielectric constant of the oxide. This problem can be addressed by using high-k dielectrics such as silicon nitride (Si3N4) that will reduce the field, increase the breakdown voltage and consequently improve the lifetime of the devices. While the advantages of single step field-plate terminated diodes are well-known, the breakdown voltage can be improved even further using a dual-step field-plate termination. Our 2D-numerical simulations using MEDICI have shown an improvement in breakdown voltages in excess of 25% compared to the traditional single-step field-plate terminated diodes.

Silicon has been the semiconductor of choice for microelectronics largely because of the unique properties of its native oxide (SiO2) and the Si/SiO2 interface. For high-temperature and/or high-power applications, however, one needs a semiconductor with a wider energy gap and higher thermal conductivity. Silicon carbide has the right properties and the same native oxide as Si. However, in the late 1990’s it was found that the SiC/SiO2 interface had high interface trap densities, resulting in poor electron mobilities. Annealing in hydrogen, which is key to the quality of Si/SiO2 interfaces, proved ineffective. This paper presents a synthesis of theoretical and experimental work by the authors in the last six years and parallel work in the literature. High-quality SiC/SiO2 interfaces were achieved by annealing in NO gas and monatomic H. The key elements that lead to highquality Si/SiO2 interfaces and low-quality SiC/SiO2 interfaces are identified and the role of N and H treatments is described. More specifically, optimal Si and SiC surfaces for oxidation are identified and the atomic-scale processes of oxidation and resulting interface defects are described. In the case of SiC, we conclude that excess carbon at the SiC/SiO2 interface leads to a bonded Si-C-O interlayer with a mix of fourfold- and threefold-coordinated C and Si atoms. The threefold coordinated atoms are responsible for the high interface trap density and can be eliminated either by H-passivation or replacement by N. Residual Si-Si bonds, which are partially passivated by H and N remain the main limitation. Perspectives for the future for both Si- and SiC-based MOSFETs are discussed.

We have performed a combined investigation of experiment and theory on the infrared reflectance from cubic SiC grown on Si by chemical vapor deposition. A damping behavior of the interference fringes away from the reststrahlen band and a dip or notch within the “flat top” are observed from some samples while they does not occur in high quality 3C-SiC/Si samples. The former is interpreted due to an interfacial transition layer existed between SiC-Si and a rough surface, while the latter can be demonstrated by a three-component effective medium model.

Silicon carbide (SiC) field-plate terminated Schottky diodes using silicon dioxide (SiO 2 ) dielectric experience high electric field in the insulator and premature dielectric breakdown, attributed to the lower dielectric constant of the oxide. To alleviate this problem we explore the use of high- k dielectrics, silicon nitride (Si 3 N 4 ) and sapphire (Al 2 O 3 ), on 4H-SiC by numerical simulations using Medici. The simulation results show significant improvement in blocking voltages by as much as 30% and much lower electric field within the dielectrics. There is also a slight reduction in the specific-on resistance ( R sp-on ) and a small increase in the forward current density due to the formation of an accumulation layer in SiC where the metal overlaps the dielectric. This effect is enhanced with increasing dielectric constant and decreasing dielectric thickness for a given dielectric.

A depletion mode metal–oxide–semiconductor field effect transistor (MOSFET) has been fabricated using 4H-SiC. The basic structure is the same as that of a conventional metal–semiconductor FET (MESFET), except that the Schottky barrier gate is replaced by a MOS gate that comprises a 50 nm silicon oxide (SiO2). The device has a pinch-off voltage of −1.0 V and a flat band voltage of 4.0 V. The drain current of the device can be substantially increased compared to the case of MESFET when a large positive gate voltage is applied, resulting in strong accumulation of electrons in the n-channel. Specifically, at a drain voltage of 25 V, the drain current is found to increase by 3.3 times when VGS is increased from 4.0 V (flat band condition) to 11.0 V (strong accumulation). Such gate bias condition, which is not possible in MESFETs, renders such devices ideal for high power applications. The electron mobility in the accumulation layer was found to be about 17.5 cm2/V s.

Reactive ion etching of 4H-SiC was performed using a CHF"3-O"2 plasma. The etch rate and mean surface roughness were investigated as a function of the ratio of the O"2 flow rate to the total gas flow rate. It was found that oxygen plays an indirect role in contributing to the etching of SiC. An optimum O"2 fraction of 20% was found to give a maximum etch rate of 35nm/min. On the other hand, the root-mean-square (RMS) surface roughness was found to increase from 1.31 to 2.34nm when the O"2 fraction increased from 0% to 80%. Auger electron spectroscopy results for the samples etched at the optimum condition of 20% O"2 fraction revealed the presence of oxygen on the etched surface in a form of an oxide-like layer (SiO"x). No carbon residue (carbon rich-layer) and aluminum were found. Based on our results, the role of O"2 in the reactive ion etching of 4H-SiC will be presented.

4H-SiC Schottky barrier diodes (SBDs) were fabricated and characterized from room temperature to 573K using HfN"xB"y as Schottky electrodes. The results are compared to SBDs fabricated using other electrodes that include Ni, Pt, Ti and Au. The Schottky barrier height @F"b for as-deposited HfN"xB"y/n-/n+ diodes, determined from room temperature current-voltage characteristics, is 0.887eV. This is lower than those of SBDs fabricated using other metals such as Au, where @F"b is 1.79eV. The HfN"xB"y/n-/n+ diodes studied have a much higher on-resistance R"o"n of around 38.24m@W-cm^2, which is about four times that of Au/n-/n+ diodes, due to the higher sheet resistance of the sputtered HfN"xB"y electrode layer. The barrier height @F"b and ideality factor @h of the HfN"xB"y/n-/n+ diodes remain almost unchanged after 400 and 750^oC anneal in N"2. This suggests excellent thermal and chemical stability of HfN"xB"y in contact with 4H-SiC.

A double recessed SiC MESFET was proposed and its electrical performances were studied by numerical simulation. Our simulated results showed that the saturation current of the double recessed structure is about 77% larger than that of the conventional structure. However, their threshold voltages are comparable and are -9.2 and -8.4V for the double recessed and conventional structure, respectively. The output power density of the double recessed structure is about 37.5% larger than that of the conventional structure though its breakdown voltage is lower. The cut-off frequency (f"T) and the maximum oscillation frequency (f"m"a"x) of the double recessed structure are 15.3 and 70.6GHz, respectively, which are higher than that of the conventional structure. Therefore, the double recessed 4H-SiC MESFET has superior DC and RF performances compared to the similar device based on the conventional structure.

Reactive ion etching (RIE) of bulk 4H-SiC based on CHF"3-O"2 plasma was studied by varying the rf power and process pressure. The elements on the etched surface and the surface roughness were characterized by Auger electron spectroscopy and atomic force microscopy, respectively. It was found that the surface roughening is mainly caused by Al contamination and C rich layer (C residues) induced micromasking effect. The micromasking effect is in turn determined by the dc self-bias developed at the substrates. A threshold dc self-bias exists at around -320 to -330V, beyond which no micromasking effect was observed. This observation is explained in terms of physical ion bombardment and sputtering in the RIE process.

An improved analytical three-region model is proposed for short-channel SiC metal semiconductor field effect transistors (MESFETs). It takes into account two regions in the channel under the gate, and a third ungated high field region between the gate and the drain. This third region, which has been omitted in SiC MESFETs analytical models reported so far, experiences a large potential drop in short channel devices operating under high drain voltages. Therefore, its inclusion is critical in providing an accurate device modeling. To further improve our model, we have also incorporated parasitic resistances and incomplete ionization of dopants. Using this three-region analytical model, we have simulated the I-V characteristics of SiC MESFET with a [email protected] gate length, and obtained excellent agreement when compared with published experimental results.

Thermally grown oxide on 4H-SiC has been post-annealed in diluted N"2O (10% N"2O in N"2) at different temperatures from 900 to 1100^oC. The quality of the nitrided oxide and the SiO"2/4H-SiC interface was investigated by AC conductance and high frequency C-V measurements based on Al/SiO"2/4H-SiC metal-insulator-semiconductor (MOS) structure. It is found that N"2O annealing at 1000^oC produces the lowest interface state density, though the difference is not so significant when compared to the other samples annealed at 900 and 1100^oC. These results can be explained by the high temperature dynamic decomposition process of N"2O. By fitting the AC conductance data, it is found that higher temperature nitridation increases the capture cross-section of the interface traps.

Reactive ion etching of SiC induced surface damage, e.g., micromasking effect induced coarse and textured surface, is one of the main concerns in the fabrication of SiC based power devices [1]. Based on CHF3 + O2 plasma, 4H-SiC was etched under a wide range of RF power. Extreme coarse and textured etched surfaces were observed under certain etching conditions. A super-linear relationship was found between the surface roughness and RF power when the latter was varied from 40 to 160 W. A further increase in the RF power to 200 W caused the surface roughness to drop abruptly from its maximum value of 182.4 nm to its minimum value of 1.3 nm. Auger electron spectroscopy (AES) results revealed that besides the Al micromasking effect, the carbon residue that formed a carbon-rich layer, could also play a significant role in affecting the surface roughness. Based on the AES results, an alternative explanation on the origin of the coarse surface is proposed.

The drain-induced barrier lowering (DIBL) effect in 4H-SiC MESFETs has been studied using the physical drift and diffusion model. Our simulation results showed that the high drain voltage typically applied in short-channel 4H-SiC MESFETs could substantially reduce the channel barrier and result in large threshold voltage shift. It is also found that the DIBL effect is more dependent on the ratio of the gate length to channel thickness (Lg/a), rather than the channel thickness itself. In order to minimize the DIBL effect, the ratio of Lg/a should be kept greater than 3 for practical 4H-SiC MESFETs.

In this work, we present results on the study of bonding and concentration of carbon in 4H-SiC MOS structure by x-ray photoelectron spectroscopy (XPS). The XPS spectra were fitted by several Gaussian lineshape functions. It is found that the so-called carbon clusters (C-C bonds) appear at the interface of SiO2/SiC, but are not seen in the oxide bulk. However, there are still some SiOxCy and Si-C bonds inside the oxide and the integrated area ratio of SiOxCy/Si-C bonds increases when further away from the SiO2/SiC interface. These observations can be interpreted in terms of the dynamic oxidation process that transforms Si-C bonds into SiOxCy bonds, which are then further oxidized to form SiO2 bonds.

The relationship between nitrogen content and interface trap density (Dit) in SiO2/4H–SiC near the conduction band has been quantitatively determined. Nitridation using NO significantly reduces Dit near the conduction band, but the effect saturates after ≈2.5×1014 cm−2 of nitrogen. These results are consistent with a model of the interface in which defects such as carbon clusters or silicon suboxide states produce traps with energies corresponding to the sizes of the defects. Nitrogen passivation results in the dissolution of the defects, which then lowers the energies of the traps in the band gap.

The crystal quality of a 4H-silicon carbide (4H-SiC) epitaxial layer is crucial to the development of high-performance 4H-SiC-based electronic power devices. However, the quality assessment of 4H-SiC homoepitaxial thin film is problematic because the same bulk material interferes with the probe of the epilayer. In this paper, we propose a simple and straightforward strategy to assess the quality of a homoepilayer using ultraviolet (UV) Raman spectroscopy (RS). Rather than focusing on the normally allowed modes, we shift our attention to the forbidden modes instead. We demonstrate that forbidden modes, which were usually ignored, are more sensitive to the crystalline imperfection and can be an effective quality probe. Our approach analyzes the crystal quality swiftly, without the need for the data fitting involved in the conventional method, and therefore makes the quality assessment much more efficient. The new method may also be applied to the other thin film materials.

A series of cubic 3C–SiC/Si samples with different thicknesses grown by chemical vapor deposition (CVD) was studied by Raman spectroscopy using laser excitation with different wavelengths plus spectral line shape analysis via two theoretical methods. Through comparative UV and visible excitation Raman measurements and theoretical analysis, the TO intensity was mainly affected by laser penetration depth and crystalline quality. The difference spectra were utilized to remove the second-order Raman signal from Si substrate. Using theoretical Raman simulation on LO-phonon and plasmon-coupling (LOPC) mode, the top layer near to the surface has big difference in electrical and optical properties compared to the deeper layer.

A graphite mask was used to realize selective doping of aluminum/boron in 4H–SiC by thermal diffusion at a temperature range of 1800–2100 °C. The doping profiles investigated by secondary ion mass spectrometry show that a high aluminum concentration of 5×1019 cm−3 near the surface and linearly graded boron profile up to several micrometers in depth can be obtained. Hall effect measurement was also employed to obtain the electrical characteristics of the diffused region, from which the carrier concentration (1×1019 cm−3) and hole mobility (7 cm2/V s) at room temperature were extracted. Room temperature photoluminescence indicates that the dominant luminescence is attributed to the donor acceptor pair recombination, in which boron D complex is the prevailing center rather than Al and boron shallow acceptors. Cathodoluminescence micrographs clearly illustrate a pattern with the locally diffused regions. To confirm the viability of the diffusion process, planar p-n diodes with a fairly low forward voltage dro...

Interface state density and channel mobility have been characterized for 4H-SiC MOSFETs fabricated with dry thermal oxides and subsequently passivated with nitric oxide. The interface trap density at 0.1 eV below the conduction band edge decreases from approximately 8×1012 to 1×10 12 eV −1 cm −2 following anneals in nitric oxide (NO) at 1175 °C for 2 h. The room temperature field effect channel mobility increases by an order of magnitude to approximately 35 cm2/V s following the passivation anneal. The field effect channel mobility of passivated MOSFETs shows almost no change with increasing temperature, while the mobility for unpassivated devices increases with increasing temperature and is thermally activated (∼T1.9) due to decreased Coulomb scattering by electrons trapped at the acceptor-like interface states near the conduction band. Over the temperature range 300–473 K, threshold voltage changes of about −0.8 and −3.7 V, respectively, are observed for devices processed with and without NO passivation.

A process is described to enhance the diffusion rate of impurities in silicon carbide so that doping by thermal diffusion can be done at lower temperatures. This process involves depositing a thin film consisting of an oxide of the impurity followed by annealing in an oxidizing ambient. The process uses the lower formation energy of silicon dioxide relative to that of the impurity-oxide to create vacancies in silicon carbide and to promote dissociation of the impurity-oxide. The impurity atoms then diffuse from the thin film into the near-surface region of silicon carbide.

An optimized multiple floating guard ring structure is investigated for the first time as an edge termination method for high voltage 4H-SiC planar devices. Simulations were performed to investigate SiC guard ring termination, and determine the optimum guard ring spacing for planar diodes with up to four floating rings. Simulated optimized designs predicted breakdown values from 40% of the ideal breakdown with a single ring, to 84% of the ideal value for diodes with four rings. Implanted 4H-SiC pn diodes with optimized guard ring designs were fabricated and results correlated to simulation. Experimental breakdown values of 1.2–1.3 kV for guard ring structure with four rings were in good agreement with simulated results.

We report results from three distinct but related thrusts that aim to elucidate the atomic-scale structure and properties of the Sic-SiO{sub 2} interface. (a) First-principles theoretical calculations probe the global bonding arrangements and the local processes during oxidation; (b) Z-contrast atomic-resolution transmission electron microscopy and electron-energy-loss spectroscopy provide images and interface spectra, and (c) nuclear techniques and electrical measurements are used to profile N at the interface and determine interface trap densities.

The orientation dependence of lateral overgrowth and vertical growth of InP deposits selectively grown through stripe openings in a phosphosilicate glass mask was investigated using halide vapor-phase epitaxy. The lateral overgrowth was observed to be strongly dependent on the orientation of stripe openings, and the vertical growth was shown to be inversely correlated to the lateral overgrowth. For a sufficiently long growth time, the growth fronts of lateral overgrowth layers from adjacent stripe openings merged together to form a completely overgrown layer. The morphology of the region where the growth fronts are merged was shown to be dependent on the orientation of stripe openings through which the growth was seeded. We also investigated a method to separate the completely overgrown layer from the substrate. This mechanical epitaxial lift-off technique may be used for hybrid integration of optoelectronic and electronic devices.

A series of 4H-silicon carbide (SiC) epilayers grown on 4H-SiC substrates by low pressure chemical vapor deposition (LPCVD) with different silane (SiH4) to propane (C3H8) gas flow ratios were studied by angle resolved X-ray photoelectron spectroscopy (ARXPS) and atomic force microscopy (AFM). ARXPS revealed that the surfaces of the samples consisted of elemental Si, Si oxides (SiO2 and SiOx where x

Tantalum pentoxide (Ta"2O"5) deposited by pulsed DC magnetron sputtering technique as the gate dielectric for 4H-SiC based metal-insulator-semiconductor (MIS) structure has been investigated. A rectifying current-voltage characteristic was observed, with the injection of current occurred when a positive DC bias was applied to the gate electrode with respect to the n type 4H-SiC substrate. This undesirable behavior is attributed to the relatively small band gap of Ta"2O"5 of around 4.3eV, resulting in a small band offset between the 4H-SiC and Ta"2O"5. To overcome this problem, a thin thermal silicon oxide layer was introduced between Ta"2O"5 and 4H-SiC. This has substantially reduced the leakage current through the MIS structure. Further improvement was obtained by annealing the Ta"2O"5 at 900^oC in oxygen. The annealing has also reduced the effective charge in the dielectric film, as deduced from high frequency C-V measurements of the Ta"2O"5/SiO"2/4H-SiC capacitors.

In this paper, we summarise the efforts of our group in the development of cost effective plasma devices for applications in the treatment of materials, in particular bio-medical materials.

Raman microprobe measurements have been made on several 4HSiC epilayers grown by low-pressure chemical vapor deposition (LPCVD). The peak intensity of the TO phonon at 795.7 cm −1 normalized by that of the TO phonon at 775.0 cm −1 was found to vary with the growth conditions as well as localized microstructural disorder. The relative intensity of the LO peak at 961.6 cm −1 was also affected by localized microstructural disorder. The dependence of the relative intensities of these two Raman scattering peaks on the morphology as well as the growth conditions provides important insight into the application of Raman scattering measurements to evaluating the quality of 4HSiC epilayers.

Raman scattering and photoluminescence (PL) under near-UV excitations were used to assess the 6H-SiC films epitaxied on 6H-SiC by low pressure vertical chemical vapour deposition (LPV-CVD). Raman linewidths and relative intensities with respect to the PL emissions were used to characterize the quality of the 6H-SiC films. Ti-related PL and outgoing resonance Raman scattering were studied. Samples grown by LPV-CVD with different growth parameters were compared on the basis of their Raman-PL spectra. This study showed that a combination of Raman and PL measurements can be used as a convenient method to assess the 6H-SiC/6H-SiC homoepitaxial structures.