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A study of the optoelectonic properties of high-resistivity p-type hexagonal silicon carbide (6H-SiC) reveals that the 6H-SiC devices exhibit high-speed photovoltaic response to laser excitations. The study is performed using lateral photoconductive switches that measure the photovoltaic and photoconductive effects. 6H-SiC devices have an efficiency of 80%.

A study of the physical changes of As-grown Czochralski silicon samples subjected to different temperatures reveals that loss of oxygen at low temperatures obeys second-order kinetics. The samples used have different oxygen concentrations. The loss of oxygen according to second-order kinetics is explained by the diffusivity of oxygen, which is larger than the normal rate of diffusivity by a factor of 3.

SnO2 a-SiC:H Au subjected to irradiation of red light exhibits a two-way photocurrent multiplication. The photocurrent multiplication is explained by a model which is developed on the phenomenon of electron tunneling through Schottky barriers. A Fowler-Nordheim type conduction is exhibited by the dark current in the high applied voltage region of SnO2 SiC:H Au.

Deep level transient spectroscopy of n-type silicon carbide shows deep traps, caused by vanadium atoms. Lines in the IR spectrum in the same spectral range of 7000-7700 per cm confirm this. The presence of vanadium atoms is identified to be a bulk defect, occurring at Ec-0.71 eV. It results in the formation of semi-insulating substrates and the reduction in the lifetime of minority carriers.

Addition of silicon barrier enhancement layers to a-Si:H/a-SiC:H double barrier structure results in a negative differential resistance current/voltage curve having a high peak-to-valley ratio. The addition is done in the collecting and injecting diode regions. The enhancement layers reduce leakage current and increase resonant tunneling current, and are more effective than crystalline AlGaAs/GaAs double barrier diodes. A primary model simulating these data account for the validity of enhancement layers.

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and infrared (IR) absorption techniques are used to study the effects of 30 kiloelectric volts of positively charged nitrogen ions implanted in amorphous silicon carbide films, deposited on silicon substrates by radio frequency sputtering over a fluence range of 1 times 10 to the power 16 -2 times 10 to the power 17 ions cmto the power -2. The chemical state evolution of silicon, carbon and nitrogen, and the vibrational features of the film components are used to discover the ion-induced modifications of these films.

High concentrations of nitrogen donors, with a binding energy of 54 million electron volts, is found in the silicon carbide grown by the chemical vapor depositions process on silicon. Conventionally, the two donors are considered as the same. In the regions of low concentrations, the isolation substitutional nitrogen is the 54 million electron volt donors.

The feasibility of using n-type beta-silicon carbide asmaterial for high-temperature piezoresistive sensors is examined through a study of its gauge factor and temperature coefficient of resistivity at variousdoping densities. The material's piezoresistive characteristics is experimentally verified to have superior gauge factors over standard foil gauges and mechanical properties suited for sensing strain at high temperatures.

A proposed design for a high-gain amorphous silicon/amorphous silicon germanium bulk barrier phototransistor for infrared light detection is presented. Results show that high gain is generated by large bulk barrier lowering in situations of light illumination and dark current retardation. Also, the introduction of an additional amorphous silicon carbide thin-film layer at the base and collector interface.

A discussion of the calculation of the electrical and thermal parameters for silicon carbide devices is presented along with a theoretical analysis of the performance of power rectifiers and metal oxide semiconductors (MOS). Results show that the development of silicon carbide Schottky devices leads to power MOS field-effect transistors which are capable of very fast switching speeds in power circuits with high breakdown voltages.

The effects of radio frequency power and substrate temperature on the structural and optoelectronic properties of hydrogenated amorphous silicon alloys are studied. Various tests, such as Raman scattering, conductivity and absorption spectra measurements, are performed on alloy films deposited on various substrates. Results show that the hydrogen concentration in the film isinversely proportional to the substrate temperature. The total fraction of carbon incorporated in the film is also found to vary directly with the radio frequency power.

The effect of wet and dry oxidation processes on the electrical properties of metal-oxide-semiconductor (MOS) capacitors on silicon carbide structures is studied. Ultrasonically agitated silicon carbide substrates with thermal oxide layer deposition are subjected to wet and dry oxidation at a maximum temperature of 1250 degrees centigrade. The capacitance-voltage characteristicsof the MOS devices are then measured under illumination at a frequency range of100 hertz to one megahertz. Results show that the samples exhibit accumulation,depletion and inversion region under illumination.

Experiments were conducted to simplify and enhance thermomigration technology and overcome the drawbacks of multiple-channel circuitry. Silicon wafers were coated with silicon carbide powder and heated by infrared lamps to obtain a high wafer temperature and gradients, in order to decrease the liquid's random walk and increase the energy flow. Temperature gradients increased and average wafer temperatures rose 10 percent, due to increased radiant energy absorption in the wafer. The thermomigration of tiny aluminum pads through a silicon wafer was made possible by raising wafer temperature and gradients.

The phase stability of two MAX phases, [V.sub.3]Si[C.sub.2] and [V.sub.2]SiC is investigated, by means of first-principles total-energy calculation within the generalized-gradient approximation and the projector-augmented wave method. It is suggested that the two MAX compounds should be possible to synthesize as stable (or metastable) phases.

High-quality Schottky junctions are fabricated on n-type 4H SiC epitaxial layers grown by chemical-vapor deposition (CVD) on C- and Si-face substrates to understand the effect of growth direction on the growth mechanism and formation of defects. The Schottky junction fabricated on C-face SiC epilayers have displayed a lower leakage current, as compared with that of Si-face epilayers.

Electrical and optical activity of boron incorporated in p-type 4H- SiC layers was observed. Under cathodoluminescence (CL) excitation, efficiency of deep boron related luminescence in compensated material depends on the concentration of attendant impurities (Al, N) and the concentration ratio of AI to N atoms.

Research describing nanopipe/dislocation defects in silicon carbide wafers is presented. Physical insight into the nature of the defects is obtained by use of ballistic electron emission microscopy.

Research into the availability of using porous silicon as semi-insulating substrate for beta-SiC high temperature optical sensing devices is presented. The high resistivity and the flexibility of the porous silicon improve the high temperature optical performance of the beta-SiC device.

An investigation is presented into the electrical and recrystallization properties of MeV P implanted 6H-silicon carbide at room temperature and 850 deg C.

High-quality aluminum nitride thin films were fabricated on a heavily-doped n-type 6H silicon carbide substrate using pulsed laser. The thin films' dielecteric properties were examined at temperatures ranging from 25 to 450 degrees Celsius. Results show capacitor leakage current densities of low 10(super -8) A/cm2 at 25 degrees Celsius and mid 10(super -3) A/cm2 at 450 degrees Celsius for a 1.7 MV/cm dielectric field. The high-temperature leakage mechanism is believed to be Schottky emission with a zero-field barrier height of 1.76 electronvolt.

The finite-element semiconductor device SPISCES was used to predict the dc I-V characteristics of a 4H-silicon carbide JFET at 773 K and its performance in a Class A power amplifier As. It was predicted from calculations that gate leakage and breakdown effects will not impede the useful operation of a 4H-SiC JFET at 773 K. Results also indicate that a Class A power amplifier using a 4H-SiC JFET can run at low frequency at a voltage gain of 4.29, a power-added efficiency of 13.3% and a 1-dB compression point power density of 0.953 W/mm.

The turn-on performance of 4H-Silicon Carbide (SiC) npnp thyristors are influenced by factors such as critical charge density, residual voltage, spread velocity and the rise time constant of the anode current. A comparative analysis involving similar silicon and Gallium Arsenide thyristors revealed the superiority of SIC in terms of pulsed turn-on performance and rise time.

An edge termination technique for 4H-silicon carbide devices based on the self-aligned implantation of a neutral ion at the edge results in higher breakdown voltages than those obtained for mesa edge terminated diodes. Experimental study of argon implantation at the edges of Schottky barrier diodes shows a small spread in the breakdown voltage suggesting the removal of edge effects in the terminated diodes. The reduced edge electric field is related to the creation of a thin high resistivity layer at the surface beyond the edges of the diodes due to argon implantation.

Specific contact resistances of Ni ohmic contacts to 6H-SiC are measured at very high temperatures. The measurements are performed using the linear transmission line technique. The measurements reveal that the temperature is inversely proportional to the contact resistance.

Admittance spectroscopy helps analyze the nitrogen donor states of Schottky barriers developed at various frequencies on n-type epitaxial 6H-SiC layers. The spectroscopic measurements yield accurate values for the ionization energies of the donor states. Two electron traps present in the energy levels associate with cubic and hexagonal sites of nitrogen donor states.

The effect of electrochemical oxidation in nitric acid on the electronic properties of epitaxial graphene (EG) grown on silicon carbide substrates is examined. The electro-oxidized channel has displayed higher values for the on-off ratio and the mobility of the graphene field-effect, which is attributed to the availability of high-quality internal graphene layers after electro-oxidation of the more defective top layers.

The 3[omega] technique is used for studying the thermal conductivity of icosahedral boron arsenide ([Ba.sub.12][As.sub.2]) films grown on (0001) 6H-SiC substrates by chemical vapor deposition. The decrease in room temperature thermal conductivity due to decrease in growth temperature is attributed to the differences in the impurity concentration and microstructure and also Seebeck coefficients are determined for the samples.

The interaction of cesium (Cs) atom/ion with the oxidant and carbon cluster defects at the SiC/Si[O.sub.2] interface is examined by using atomistic scale computational methods and characterization methods. The results have shown that Cs has not reduced the penetration barrier of the impinging oxidant.

Several studies are conducted to explain the donor-acceptor pair luminescence that is exhibited by the different P-Al and N-Al pairs in the 3C-SiC compound. These studies also help in the determination of the ionization energy of the phosphorus donor present in the system.

A molecular dynamics (MDs) simulation and micromechanics bridging method are used for examining the thermoelastic properties of SiC/epoxy nanocomposites. A micromechanics-based scale bridging method is described that has handled both the elastic and residual fields of the nanocomposites with the help of the effective interface concept and sequential information transfer.

Intentionally doped n-type 4H-SiC films are grown on 4[degree] and 8[degree] off-axis substrates in order to examine the impact of electron concentration on the incorporation of electron traps [Z.sub.1/2] and E[H.sub.6/7]. Carrier lifetimes in 8[degree] material are slightly longer than in 4[degree] films for similar doping concentrations, which is associated with surface recombination and extended defects.

Free electron concentration and carrier mobility measurements on 4H-SiC metal-oxide-semiconductor inversion layers are described. The measured free carrier concentration is modeled by using the charge-sheet model and the mobility is modeled by existing mobility models.

The temperature dependence of electrical resistivities and deep levels in semi-insulating 6H-SiC bulk wafers is analyzed. The results have shown that although the deep levels have major impact on resistivity for semi-insulating n-type 6H-SiC, there are unobserved deep levels compensating acceptors.

The formation of the various recombination-induced stacking faults (SFs) within the 4H-SiC bipolar and unipolar devices is explained. The various conditions under which the SF contraction and forward voltage drift recovery is induced are also analyzed.

Several density-functional theory calculations are conducted to explain the electronic structures of the negatively-charged nitrogen-silicon-vacancy center present in cubic silicon carbide (3C-SiC). The results demonstrate that the 3C-SiC compound can be easily employed for the generation of a solid state qubit operation.

The dominant recombination processes controlling the carrier lifetime in n-type 4H-SiC epitaxial layers grown with low concentrations of the [Z.sub.1/2] defect are examined by analyzing the variation in the carrier lifetime with temperature. The studies have shown that further enhancement of the total lifetime under the high injection conditions of a device structure has required very thick epilayers, effectively passivated surface and interface recombination and a further reduction in the remaining [Z.sub.1/2] concentrations.

The effects of thermal oxidation on deep levels in the whole energy range of the band gap 4H-SiC are examined by using deep level transient spectroscopy. The dominant defect IP4 observed in p-type 4H-SiC after thermal oxidation is reduced by subsequent annealing in Ar, where these phenomena are explained by a model that excess interstitials are generated at the oxidizing interface, which has diffused into the bulk region.

Several studies are conducted to explain the impact of the forward current stress on the low frequency noise exhibited by the different 4H-SiC p-n junctions. The stress is shown to lead to the onset of the burst noise in these junctions.

Several capacitance-voltage measurement are conducted to analyze the electron states present at the 4H- SiC/Si[O.sub.2] interface. True interface, fast near interfaces and slow near interfaces are shown to be the three main states demonstrated by the analysis.

The deep level transient spectroscopy technique is employed to explain the different deep levels that are induced by the reactive ion etching in n- and p-type 4H- SiC compounds. The concentration of the defects is shown to decrease because of thermal oxidation.

The time-resolved free carrier absorption technique is employed to explain the different carrier recombination transients taking place in the 4H- SiC crystals. These crystals are shown to exhibit highly enhanced surface recombination rate at high excitation conditions.