High-resolution X-ray diffraction is one of the most powerful and widely used techniques for accurate characterization of the lattice parameters, mismatch, alloy composition, dopant concentrations, and thickness of epitaxial materials. In this presentation, we use a series of advanced X-ray diffraction techniques, including double-axis diffraction, triple-axis diffraction, reciprocal space mapping (RSM), and synchrotron white beam X-ray topography, to characterize highly nitrogen-doped homoepitaxial 4H-SiC epilayers. Measurements reported in this work have determined that in single crystal 4H-SiC, increasing the nitrogen doping level above 4 × 1017 cm#x2212;3 results in corresponding increase in lattice contraction. The increase in epilayer/mismatch mismatch with doping, and the corresponding strain energy, is attributed to the substitutional nitrogen incorporated preferentially in the host carbon sites of the 4H-SiC epilayer. Also, significant lattice tilts, generally along the [1120] offcut direction (8°), exist, which are believed to be induced by the Nagai epitaxial tilt.

4H-SiC samples are bent in compression mode at 550°C and 620°C. The introduced-defects are identified by Weak Beam and HRTEM techniques. They consist of double stacking faults bounded by 30° Si(g) partial dislocations whose glide locally transforms the material in its cubic phase. The velocity of partial dislocations is measured after chemical etching of the sample surface. The formation and the expansion of the double stacking faults are discussed.

Charge controlled power switching devices fabricated in 4H-Silicon Carbide are discussed in this paper. After comparing possible structures, results on prototype devices are presented. The presentation will give an overview about the developments of SiC power switches at SiCED, in addition some potential applications serving as an accelerator for the SiC power switch development will be sketched. The performance of vertical JFETs will be analyzed in detail. These can be operated as a single device as well as in combination with a low voltage silicon power MOSFET. The result of the hybrid assembly is a normally off device which behaves for the user more and more like a classical MOSFET with respect to the input as well as the output characteristic. Several improvements where performed which make the device more attractive for the customer. It will be shown which factors drive these optimization and how they can be implemented. Although the primary target for this device is the >1000V blocking voltage range, it will be discussed how the huge 600V power switch market can be made accessible for SiC power devices too. Intensively the high temperature performance of SiC JFETs and Si/SiC cascodes is discussed. Additionally, other developments like silicon power MOSFETs or high voltage switches will be mentioned.

A method is presented for detecting, counting and mapping micropipes and dislocations in n+, undoped, and semi-insulating Silicon Carbide wafers. The technique is based on etching in molten Potassium Hydroxide (KOH), and it employs image processing that automatically detects etch pits, discriminates between micropipes and dislocations, and generate micropipe and dislocation density maps. We demonstrate a novel way of detecting and mapping dislocations and micropipes in semi-insulating SiC. This is achieved by combining a properly tuned etching technique that reliably produces well defined etch pits with image processing that enables quick and accurate analysis of the etch pit contrast. We show that the results of optical evaluation are close to those obtained using the Synchrotron White Beam X-Ray Topography (SWBXT) technique.

As a high mobility, wide bandgap semiconductor, 3C-SiC has great promise. In this paper, we examined to obtain 3C-SiC epilayer on Si substrates using hot-wall CVD furnace and report the use of hexamethyledisilane (HMDS) and propane as reaction gases to grow uniform thickness on 2 inch (100), (111), (110) and (211) orientation of Si substrates. A horizontal atmospheric pressure CVD reactor was used. A reaction zone was specially designed. To obtain uniform thickness of the epilayer, inside of the suscceptor hole was intentionally tapered along flow direction as follows; inlet of the square hole is 13 mm × 60 mm and outlet of the hole is 7 mm × 60 mm, and laminar channel for changing the gas flow profile was managed. The susceptor was surrounded by graphite foam. Temperature of the suscepotor was measured at inside wall of the susceptor by optical pyrometer. H2 flow rate for etching was 3 slm. An initial carbonization procedure was performed using 0.9 sccm propane at 1250 oC for 2-3 minutes. During the growth of SiC at 1300 °C, the flow rate of HMDS was 0.75-1.2 sccm and the flow rate of propane was 0.1 – 0.5 sccm. The hydrogen carrier gas flow rate was 3-10 slm. Typical growth rate was 4.5 micron /h. Uniform thick 3C-SiC was obtained. The samples were examined using ultra violet light spectrometer and RHEED.

This paper presents experimental atomic force microscope (AFM) observations of the surface morphology of as-grown (111) silicon-face 3C-SiC mesa heterofilms. Wide variations in 3C surface step structure are observed as a function of film growth conditions and film defect content. The vast majority of as-grown 3C-SiC surfaces consisted of trains of single bilayer height (0.25 nm) steps. Macrostep formation (i.e., step-bunching) was rarely observed, and then only on mesa heterofilms with extended crystal defects. As supersaturation is lowered by decreasing precursor concentration, terrace nucleation on the top (111) surface becomes suppressed, sometimes enabling the formation of thin 3C-SiC film surfaces completely free of steps. For thicker films, propagation of steps inward from mesa edges is sometimes observed, suggesting that enlarging 3C mesa sidewall facets begin to play an increasingly important role in film growth. The AFM observation of stacking faults (SF's) and 0.25 nm Burgers vector screw component growth spirals on the as-grown surface of defective 3C films is reported.

Silicon carbide (SiC) based gas sensors have the ability to meet the needs of a range of aerospace applications including leak detection, environmental control, emission monitoring, and fire detection. While each of these applications require that the sensor and associated packaging be tailored for that individual application, they all require sensitive detection. The sensing approach taken to meet these needs is the use of SiC as a semiconductor in a Schottky diode configuration due to the demonstrated high sensitivity of Schottky diode-based sensors. However, Schottky diode structures require good control of the interface between the gas sensitive metal and SiC in order to meet required levels of sensitivity and stability. Two examples of effort to better control the SiC gas sensitive Schottky diode interface will be discussed. First, the use of chrome carbide as a barrier layer between the metal and SiC is discussed. Second, we report the first use of atomically flat SiC to provide an improved SiC semiconductor surface for gas sensor deposition. An example of the demonstration of a SiC gas sensor in an aerospace applications is given. It is concluded that, while significant progress has been made, the development of SiC gas sensor systems is still at a relatively early level of maturity for a number of applications.

4H-SiC(0001), (000-1), and (11-20) have been directly oxidized by N2O at 1300°C, and the MOS interfaces have been characterized. The interface state density has been significantly reduced by N2O oxidation on any face, compared to conventional wet O2 oxidation at 1150°C. Planar n-channel MOSFETs fabricated on lightly-doped 4H-SiC(0001), (000-1) and (11-20) faces have shown an effective channel mobility of 26, 43, and 78 cm2/Vs, respectively. The mobility decreased with increasing the doping concentration of p-body. SIMS analyses have revealed a clear pile-up of nitrogen atoms near the MOS interface. The thickness of interfacial SiCxOy layer can be decreased by utilizing N2O oxidation. The crystal face dependence of interface structure is discussed.

The electric field dependence and anisotropy of the impact ionization coefficients of 4H-SiC are investigated by means of the avalanche breakdown behavior of p+n diodes. The breakdown voltages as a function of doping density and the multiplication factors of a leakage current are obtained using p+n diode fabricated on (0001) and (1120) 4H-SiC epitaxial wafers. The obtained impact ionization coefficients show large anisotropy; the breakdown voltage of a p+n diode on (1120) wafer is 60% of that on (0001) wafer. We have shown that anisotropy of the impact ionization coefficients is attributable to the anisotropy of saturation velocity originated from the electronic structure of 4H-SiC.

In the present work, strong room-temperature photoluminescence (PL) at 1540 nm is reported from erbium-implanted and post-annealed amorphous silicon carbide (a-SiC:Er) films. The stoichiometric SiC films were grown by thermal chemical vapor deposition (TCVD) at 800°C, and then implanted to Er fluence of 3×1015 ions/cm2 using 380 keV implantation energy. Post-implantation annealing was carried out at the temperature range of 550°C to 1350°C in argon (Ar) ambient. The resulting SiC films were characterized by Auger electron spectroscopy (AES), Rutherford backscattering (RBS), Fourier transform infrared spectroscopy (FTIR), nuclear reaction analysis (NRA), x-ray diffraction (XRD), and high-resolution transmission electron microscope (HRTEM). Clear PL behavior was seen from the annealed a-SiC:Er samples, even at room temperature, with PL intensity reaching a maximum for samples annealed at 900°C.

Additional studies of thermal quenching of Er luminescence from a-SiC:Er samples annealed at 900°C indicated that as the sample temperature increased from 14K to room temperature, the luminescence intensity at 1540 nm dropped by a factor of ∼ 3.6. Moreover, the PL spectra of the a-SiC:Er samples did not exhibit any defect-generated luminescence. It is suggested that the lower density of Si and C vacancies in the stoichiometric a-SiC:Er, as compared to its non-stoichiometric a-Si1-xCx counterpart, along with the incorporation of a higher Er dopant concentration, can effectively diminish defect-produced luminescence and lead to a significant improvement in PL performance.

These properties suggest that stoichiometric a-SiC:Er may be a good candidate for producing optoelectronic devices operating in the 1540 nm region.

Thermal oxidation of SiC by the afterglow method has opened new pathways of opportunity to address both thin film growth and defects that hinder electronic device development with this important semiconductor material. Oxide growth, with rates up to 700Å per hour, on SiC has been demonstrated using this technique over a temperature range from 400°C to 1100°C at 1 Torr total pressure. Electrical and physical properties of oxide films grown by conventional means or by the afterglow method were obtained with a novel, non-contact charge-voltage (Q-V) metrology approach. This instrument employs a combination of incremental contact potential difference values obtained in response to applied corona charge generated from air. The slope of the Q-V characteristic within a bias range corresponding to accumulation of the semiconductor provides an effective dielectric permittivity value for the grown film. Effective permittivity values for afterglow oxides grown on SiC approach that of SiO2 grown on silicon substrates whereas the values for oxides grown on SiC in an atmospheric steam oxidation process are always depressed relative to SiO2 on silicon, indicating that the latter process always produces low-k oxides. A mechanistic discussion regarding these observed differences between the two oxidation methods is presented along with suggestions for an integrated process and metrology approach to reduce defects in oxide films on SiC.

Single and stacked p-i-n sensing elements for image recognition and color extraction applications are presented. The aim of this work is to optimize the performance of the a-SiC:H thin films layers in order to enhance its performance when making part of the structure of large area image and color sensors. The efforts are focused mainly on doped n- and p-type layers at high and low doping levels with and without carbon. The structural and optoelectronic properties of the single layers were determined through infrared and visible spectroscopy, temperature-dependent conductivity, and were complemented by CPM measurements. Junction properties, carrier transport, photogeneration and collection efficiency are investigated from dark and illuminated current-voltage characteristics and spectral response measurements, with and without additional background illumination and under different light bias conditions. The spectral response dependence on the applied voltage and on optical bias was also studied. Results show that the spectral sensitivity is strongly dependent on the applied voltage, namely the maximum spectral sensitivity shifts with the voltage, and at certain wavelengths the spectral response goes down to zero, which allows a different selectivity, and enables color recognition.

The dependence of the aluminum incorporation on the total pressure in a hot wall vapor phase reactor for SiC homoepitaxial growth has been investigated. It was found that in the doping concentration range from 1·1017 cm−3 to 1·1019 cm−3 the incorporated aluminum concentration varies by the factor 3 to 4, when the reactor pressure is changed from 150 mbar to 250 mbar. Lower reactor pressure gives lower aluminum concentration. Periodically changing reactor pressure results in aluminum concentration periodically changing with depth in the epilayer. All results were measured electrically by capacitance-voltage measurements on nickel Schottky contacts. Additional experiments have been performed for n-type nitrogen doped SiC epilayers for comparison. The nitrogen doping concentration was found to be independent of the reactor pressure within the accuracy of the applied C-V measurements and the doping profile analysis method.

Semi-insulating (SI) 6H-SiC boules up to 110mm in diameter have been grown by Physical Vapor Transport (PVT). SI properties have been achieved by vanadiumc compensation, which resulted in the room temperature electrical resistivity exceeding 2×1011ωcm. Low temperature photoluminescence (LTPL) data shows the presence of the deep intrinsic defect level UD-1 in addition to V4+. The nitrogen-bound exciton (NBE) luminescence is weak in heavily vanadium compensated 6H-SiC.

SiC single crystals have been grown by seeded sublimation method using physical vapor transport (PVT) system designed and fabricated in our laboratory. A novel multi-segmented graphite insulation has been used for improved heat containment in the hot-zone. Numerical modeling was used to obtain the temperature field and predict various growth parameters. The grown crystals were characterized using AFM, SWBXT and chemical etching.

Molten KOH etchings were implemented to delineate structural defects in the n- and ptype 4H-SiC samples with different doping concentrations. It was observed that the etch preference is significantly influenced by both the doping concentrations and the conductivity types. The p-type Si-face 4H-SiC substrate has the most preferential etching property, while it is least for n+ samples. It has been clearly demonstrated that the molten KOH etching process involves both chemical and electrochemical processes, during which isotropic etching and preferential etching are competitive. The n+ 4H-SiC substrate was overcompensated via thermal diffusion of boron to p-type and followed by molten KOH etching. Three kinds of etch pits corresponding to threading screw, threading edge, and basal plane dislocations are distinguishably revealed. The same approach was also successfully employed in delineating structural defects in (0001) C-face SiC wafers.

High-dose Al implants in n-type epitaxial layers have been successfully annealed at 1600°C without any evidence of step bunching. Anneals were conducted in a silane ambient and at a process pressure of 150 Torr. Silane, 3% premixed in 97% UHP Ar, was further diluted in a 6 slm Ar carrier gas and introduced into a CVD reactor where the sample was heated via RF induction. A 30 minute anneal was performed followed by a purge in Ar at which time the RF power was switched off. The samples were then studied via plan-view secondary electron microscopy (SEM) and atomic force microscopy (AFM). The resulting surface morphology was step- free and flat.

An overview of SiC Power Devices is provided. Progress in 1200 V SiC Schottky diodes, 1200 V SiC BJTs, 10-20 kV SiC PiN diodes and 2 kV SiC Power MOSFETs will be described. SiC Schottky diodes have already been commercialized. The next step of inserting these diodes in Si IGBT modules is happening now. Emphasis is placed on the problems and issues at the SiC device/process interface which need to be urgently addressed such as the roughness created during the implant anneals, reliability of the gate oxide under positive and negative bias, low current gain of the BJTs, forward voltage instability in the pn junctions etc. Overcoming these issues in the near future will be critical to the successful commercialization of SiC devices.

Ta2Si silicide has been deposited by sputtering and thermally oxidized on 4H-SiC and Si substrates. A mixture of SiO2 and Ta2O5 insulator films has been obtained after oxidation in dry O2. Among the high-k dielectrics, tantalum pentoxide (Ta2O5) could be a valuable alternative due to its high dielectric constant. Atomic force microscopy (AFM), C-V measurements along with x-ray diffraction analysis have been carried out in order to study the feasibility of this material as gate dielectric for 4H-SiC MOS devices. Electrical characteristics of deposited and oxidized Ta2Si on 4H-SiC and Si samples have been obtained and compared. At the range of oxidation temperatures considered (850°C-950°C), the influence of diffusion processes between the Si substrate and Ta2Si layer during oxidation strongly influences the dielectric properties of the resulting insulator layer on Si substrates.

Argon ions (Ar+) were implanted into n-type 4H-SiC epitaxial layers at 600 °C. The energy of the ions was 160 keV and at a dose of 2 × 1016 cm−2. After post-implantation annealing at 1600 °C, Schottky diodes were fabricated on the ion implanted samples. Bulk n-type 4H-SiC samples were irradiated at room temperature with 1 MeV electrons at doses of 1 × 1016 to 5.1 × 1017 el/cm2. The current density of the beam was 0.91 μA/cm2. Deep Level Transient Spectroscopy (DLTS) was used to characterize the induced defects. DLTS studies of Ar+ implanted samples showed six defect levels at EC – 0.18 eV, EC – 0.23eV, EC – 0.31eV, EC – 0.38 eV, EC – 0.72 eV, and EC – 0.81 eV. Z1/Z2 defect is the dominant defect in the electron irradiated sample and anneals out completely after 10 minutes at 1000 °C. However, Z1/Z2 defect in Ar+ implanted samples was stable up to 1600 °C. It is suggested that the annealing behavior of Z1/Z2 depends on the source of its formation.