Field Enhanced Diffusion with Optical Activation (FEDOA), a method developed in the authors' laboratory for adding impurities to diamond, has demonstrated that many types of impurities can be incorporated into natural diamond plates and CVD diamond films. This work reports the incorporation of hydrogen in type IIa diamond plates and CVD diamond films. The results indicate that hydrogen is attracted to diamond. Hydrogen is incorporated into different polycrystalline diamond films at different rates. The grain size of the diamond film seems to play a role in the rate of hydrogen incorporation. The best results for hydrogen storage (21% by mass) were with films with submicrometer grain sizes.
Summary form only given. In this work we report the reactive ion etching (RIE) of GaN using CF/sub 4//Ar and CHF/sub 3//Ar chemistries. The effects of RF plasma power, pressure and gas flow rates on the etch rate were investigated as well as the interaction of physical and chemical components of the etch process. We used 2.8 /spl mu/m, n-type GaN film, grown on Al/sub 2/O/sub 3/ substrate. It was patterned with evaporated aluminum, which was chemically removed after the etch process.
Recently the ternary compound CsPbCl/sub 3/ produced by co-evaporating CsCl and PbCl/sub 2/ has attracted much interest for its interesting optical characteristics. Indeed, aggregates with dimensions of about 10 nm are produced in the material as evidenced by luminescence spectroscopy and X-ray diffraction. Identification of the aggregates is based on a similarity of the observed emission properties with those of the bulk material. CsPbCl/sub 3/ is a wide-gap semiconductor with direct band-to-band transitions. The phase diagram of the CsCl-PbCl/sub 2/ system reveals the existence of complex ternary CsPbCl/sub 3/ (phase III semiconductor) and Cs/sub 4/PbCl/sub 6/ (phase VI, insulator) compounds. Varying the deposition rate the phase III is deposited together with the insulating phase VI. The crucible temperatures have also been optimized to control the deposition rate in order to achieve the ternary phase III only. The aim of this paper is to report on the preparation, optical and electrical characteristics of bulk and vacuum evaporated ternary compounds. To our knowledge this is the first time that the electrical behaviour in dark and in light is reported for these compounds. The correlation of the aggregate dimensions with the exciton absorption will be also introduced and discussed. X-ray diffraction spectroscopy is used as an independent evidence for aggregated phase creation. Samples used for this study have been grown by vacuum evaporation starting from Bridgman crystal chips of CsPbCl/sub 3/ or by co-evaporation of CsCl and PbCl/sub 2/ purified powders onto 7059 Coming glass substrates.
We report the application of the UV-extended multichannel ellipsometer in studies of the growth and layered structure of cBN films deposited on c-Si using pulsed dc sputtering of a B/sub 4/C target with rf substrate bias.
Silicon Carbide is a very interesting semiconductor material for high temperature, high frequency, and high power applications. The main reasons are its high saturation velocity, large thermal conductivity, high Schottky barriers, and high breakdown voltages. High quality 4H-SiC and 6H-SiC polytype substrates and epitaxial layers are commercially available today. An additional advantage of SiC is the native oxide that allows fabrication of MOS devices. A large effort has been devoted towards the development of high performance devices in SiC. The largest success has been for unipolar devices like Schottky diodes and different kinds of MESFETs. MOSFETs have also been fabricated in both 4H- and 6H-SiC. Unfortunately, the MOSFET performance was found to be much worse than expected, due to a very low surface mobility. Nevertheless, the technology developed is very interesting and includes possible large scale integration of digital circuits operating at very high temperatures. In this work we present numerical simulations of the device performance of different Field Effect Transistors (FETs). Both full band Monte Carlo simulations and macroscopic modeling using the drift-diffusion approach have been utilized in this work. The Monte Carlo simulations have been used to extract transport parameters and to evaluate the macroscopic models in a device configuration.
The principal author reports here the main elements of work performed as part of his 1999 Ph.D. dissertation (Matthew Keith West, ''Diffusion of Sulfur into Natural Diamond: Characterization and Applications in Radiation Detection''. Ph.D. Dissertation, University of Missouri-Columbia, USA (1999)). In this study a Field Enhanced Diffusion with Optical Activation (FEDOA) reactor was constructed, tested, and employed to diffuse sulfur and sodium into polished, natural diamond plates. Various chemical sources of sulfur were used for diffusion from the gaseous, liquid, and solid phases. Diffusion coefficients in the range of 10 � 15 cm 2 /s to 10 � 14 cm 2 /s for temperatures 450-1050 � C, have been calculated for sulfur from concentration profiles determined from secondary ion mass spectroscopy (SIMS) analysis. Sulfur demonstrated n-type behavior with an activation energy of 0.9 eV. Sodium was found to diffuse into diamond with an average diffusion coefficient of 7.2 � 10 � 14 cm 2 /s at 750 � C. The different sources of sulfur provided qualitative information about competing mechanisms in the diffusion process.
Nanocrystalline silicon carbide thin films were prepared by a modified vacuum arc method of deposition using a silicon carbide cathode. For modification of optical properties some films were doped by RE metals from special evaporator during deposition. Thin SiC films deposited at room temperature were amorphous and had substantial stress. The phase transition from amorphous silicon carbide to nanocrystalline silicon carbide occurred at deposition temperature 450-500/spl deg/C. The properties and structure of nanocrystalline SiC films mainly depended on the substrate temperature and energy of deposited ions.
Summary form only given. We report a parametric investigation of the etching of 4H-SiC bulk wafers and thin diamond like carbon (DLC) layers on the SiC substrates. The 4H-SiC samples were bulk substrates doped with N, and an amorphous DLC layer (/spl sim/500A thick) was deposited on the same SiC substrate by reactive pulse plasma assisted method. The reactive ion etching (RIE) method and fluorine containing plasma (CF/sub 4/) were employed and Ar and O/sub 2/ were used as a gas additive.
The author points out the improvement of tribological behaviour of a Co-Cr-Mo alloy surface modified with a nanocrystalline diamond layer by RF-PCVD. With this surface treatment it is possible to decrease the friction coefficient and wear rate of the implant alloy in respect to untreated material.
This paper presents results of charge carriers removal from 4H-SiC wafers. A new chemical reactor has been tested for forced diffusion purification (reversed diffusion) of SiC films. Different types of conditions have been used to purify SiC samples. A 5 mW (630-680 nm) laser has been used to improve results. I-V characteristic curves have been measured to verify changes in electrical properties of the samples. SIMS has been used to analyze the concentrations of impurities in the SiC samples before and after treatment. It has been demonstrated that the field enhanced by optical activation diffusion method can remove impurities such as N and B form SiC films. As a result, the electrical properties of the SiC wafers have been significantly improved during treatment, especially in cases where a laser is emplaced.
Summary form only given. Results of research on the electric properties of Ni contacts on n-type 4H-SiC are presented. The forward and reverse I-V measurements of Ni/4H-SiC Schottky rectifiers are demonstrated. The studies showed degradation of the structures over time. The lack of passivation probably caused the increase of leakage current. The scatter of Schottky diode parameters like the ideality factor, the saturation current density, the series resistance and the Schottky barrier height were studied. The Schottky barrier height was calculated from I-V characteristics measured at room temperature.
The features and advantages of multicomponent compound cathodes for vacuum electronic devices are discussed. The effects of recent experimental data on the effective work function of a composite cathode with cubic boron nitride as the principal phase, are presented. Methods to reduce the work function of new materials so as to develop high(er) efficiency cathodes, are proposed.
This paper presents results of impurity removal from 6H-SiC wafers. A new chemical reactor has been tested for Field Enhanced Diffusion by Optical Activation (FEDOA) purification (reversed diffusion) of SiC films. Different conditions have been used to purify SiC samples including temperature variation, electrical field variation, variations in electrical current and optical activation. A 5 mW (630-680 nm) laser was used for optical activation. It was observed that optical activation has a major effect on ion drift rates. It was also observed that the magnitude of the electrical current enhanced ion drift rates as well by a postulated current drag mechanism. I-V characteristic curves were obtained to verify changes in the electrical properties of the samples. SIMS was used to analyze the concentrations of impurities in the SiC samples before and after treatment. It has been demonstrated that the field enhanced diffusion by optical activation method can remove impurities such as N and B from SiC films. As a result, the electrical properties of the 6H-SiC wafers have been significantly improved during treatment especially in cases where a laser is emplaced.
Summary form only given. The market for biocompatibility materials and structures is growing steadily. Among these materials there are carbon layers, especially nanocrystalline (NCD) and diamond like carbon (DLQ) layers that are being increasingly investigated. These layers can act as biocompatible coatings as well as sensitive organic polar compounds. The layers under study were obtained on silicon substrate through low pressure plasma CVD methods. The layers were defined with the use of C-V and I-V characteristics. AFM and SEM methods were used to study the layer structure. An ellipsometric study was also conducted. This research allowed the authors to ascertain the fact that DLC and NDC layers act as dielectrics while their properties are very much dependent on the state of the layer-metal contacts. The impact of the environment for Al electrodes on the electrophysical parameters of DLC and NDC layers was also examined.
