Although many researchers have studied boron-doped diamond thin films in the past several years, there have been few reports on the effects of doping CVD-grown diamond films with phosphorous. For this work, polycrystalline diamond thin films were grown by hot filament chemical vapor deposition (HFCVD) on p-type silicon substrates. Phosphorous was introduced into the reaction chamber as an in situ dopant during the growth. The quality and orientation of the diamond thin films were monitored by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Current-voltage (I-V) data as a function of temperature for golddiamond film-silicon-aluminum structures were measured. The activation energy of the phosphorous dopants was calculated to be approximately 0.29 eV.

Epitaxial and implanted layers are generally characterized by Hall effect measurements using a pn-junction as electrical insulation of the layer from the substrate. Due to defects, low doping concentrations or thin layers the resistivity of epitaxial or implanted layers is comparable to the resistivity of the pn-junction and the substrate. This results in inefficient electrical insulation between both regions. To be able to determine the properties of epitaxial or implanted layers even in the case of substantial leakage current we developed a two-layer Hall effect measurement concept. This concept is based on the conventional van der Pauw technique applied to the layer and the substrate separately. In addition the current-voltage characteristic of the pn-junction is measured and modeled in the analysis as an ohmic resistor.

This two-layer concept is applied to epitaxial grown SiC and the results are compared with conventional van der Pauw technique. In addition both techniques are compared with the results of capacitance-voltage (CV) measurements and secondary ion mass spectroscopy (SIMS).

Undoped single crystalline aluminum nitride films were grown by metal organic chemical vapor deposition (MOCVD) at 1200 °C. The precursors used were trimethylaluminium (TMA) and ammonia (NH3) in a hydrogen carrier flow, at a pressure of 10 Torr. Silicon carbide substrates of the 4H or the 6H polytype with an epilayer on the silicon face, were used to grow the 200 nm thick A1N films. Aluminum was evaporated and subsequently patterned to form MIS capacitors for high frequency (400 kHz) capacitance voltage measurements at room temperature. It was possible to measure the structure and characterize accumulation, depletion and deep depletion. However, it was not possible to invert the low doped SiC epilayer at room temperature. From an independent optical thickness measurement the relative dielectric constant of aluminum nitride was calculated to be 8.4. The films were stressed up to 50 Volts (2.5 MV/cm) without breakdown or excessive leakage currents. These results indicate the possibility to replace silicon dioxide with aluminum nitride in SiC field effect transistors.

We present an optical study of the excitonic properties of epitaxial GaN using reflectivity and photoluminescence (PL) measurements. The values for the intrinsic exciton energies are found to be dependent on the built in strain developed due to the difference in thermal expansion coefficients between the GaN epilayer and the foreign substrate. For GaN on sapphire thecompressive biaxial strain causes an upshift of A and B excitons by typically 15 meV relative to the strain free sample, in accordance with previous data. For GaN on SiC, on the other hand, a downshift ˜ 8 meV in the free exciton energies is observed at 2K. Only two excitonic peaks about 18 meV apart, are resolved in reflectivity spectra for GaN on SiC, probably due to the overlapping of A and B excitons. The suggested explanation implies the reduction of the bandgap energy and of the valence band splitting under the action of a biaxial tensional strain in the GaN layer. For all structures the strain-induced shifts of the bandgap energy are much smaller at elevated temperatures, presumably reflecting the temperature dependence of the accumulated strain energy. The exciton-polariton structure of the GaN is also discussed. The enhanced intensity of the no-phonon (NP) A line compared to its longitudinal (LO) phonon replica is suggested to be partially attributed to strong defect scattering.

A series of GaN films grown by MBE on sapphire substrates with different nitrogen sources are characterized by optical transmission, spectroscopic ellipsometry (SE), photoluminescence (PL) and cross-sectional atomic force microscopy (AFM). The film thicknesses determined from broad spectral range transmission measurements and the AFM images are used in the analysis of the SE spectra. Interface roughnesses between the constituent layers, such as the substrate, the buffer and GaN layers are included in the modelling of the SE spectra and are also imaged by cross-sectional AFM. An effective medium type model is used for the modelling of interface and surface roughnesses in the SE spectra. The optical constants of the films in the band edge spectral range are determined in such a way as to simultaneously satisfy the transmission and the ellipsometry data.

CVD diamond could be an electroluminescent material. While its photoluminescent and cathodoluminescent properties are relatively well known, the electroluminescent ones have not been intensively investigated. The electroluminescent emission of CVD diamond is reminescent of the so-called “band A”; it is centered at 2.8 eV and extends from 2.6 to 3 eV. The luminescenceintensity increases linearly with the electric current and corresponds to a superquadratic regime of I-V characteristics in the dark and to a quadratic regime under a λ = 442 nm illumination. The I-V characteristics can be related to space charge limited current (SCLC) phenomena. Besides, the temperature behaviour of electroluminescence and of photoexcited current can be put into relation with the presence of a deep state in the bandgap where injected carriers from both electrodes recombine. The electroluminescent emission, even in a wavelength region far away from the photopic response, is clearly and strongly visible at naked eye. The luminescence efficiency is being discussed in order to consider CVD diamond as a material for optoelectronic devices.

Cathodoluminescence measurements at cryogenic temperatures are reported on boron- and phosphorus-doped CVD-diamond films grown on silicon substrates. Boron and phosphorus concentrations were determined by SIMS measurements; for boron, they reached from unintentional background doping levels up to 3500 ppm. At increasing boron concentrations, the radiative recombination of boron bound excitons (BEto) at 5.22 eV photon energy systematically broadens and shifts down to 4.99 eV whereas the free exciton emission (FEto) disappears for 40 ppm and higher. In the phosphorus-doped films we observe new lines at 5.16 eV and 4.99 eV which we ascribe to TO- and (TO+Or)-phonon assisted transitions of an exciton bound to a shallow impurity other than boron, possibly phosphorus or a phosphorus-related shallow complex.

Crystalline diamond coatings and, increasingly, diamond like amorphous carbon (DLC) films are used for tribological and protective layers for their hardness and chemical inertness. They are also under investigation for their electron emitting properties, with possible applications in field emission displays. DLC films were deposited by laser ablation using a KrF excimer laser and fluences between 0.5 and 2 J/cm2. FTIR measurements did not show the presence of hydrogen in the films. Raman spectra allowed for the determination of the nature of the graphitic and diamond bonds (sp2 and sp3) as well as information about the disorder and short range order in the films. For a better determination of the sp3-content, which is often hidden in the Raman spectra, a correlation with optical properties in the near IR to near UV region was established. These values depended strongly on the substrate temperature and the laser fluence. DLC formation could be demonstrated even at substrate temperatures close to room temperature. Vickers hardness values and first measurements on the electron emissivity of the films can be correlated to the diamond character and the preparation method of the films.

Nitrogen is the common n-type dopant of the various polytypes of silicon carbide. The nitrogen levels in 4H-SiC (at EC-53 meV and EC-100 meV) and in 6H-SiC (at EC-89 meV, EC- 100 meV, and EC-125 meV) have been studied in detail by temperature dependent Hall effect measurements, electron spin resonance (ESR), and thermal admittance spectroscopy. Until now, such detailed studies of the nitrogen levels in 15R-SiC have not been carried out.

Lely-grown 15R samples were used in these studies. The net carrier concentrations (ND-NA), determined by room temperature CV measurements, ranged from 1 × 1018 to 3 × 1018 cm−3. The nitrogen levels in 15R-SiC were studied using thermal admittance spectroscopy. Optical admittance spectroscopy (OAdS) was used to study the deeper defects in this polytype. It was found that optical transitions to the conduction band were inhibited in the heavily doped material.

The density-functional theory with ab initio pseudopotentials has been used to study the linear optical response of semiconductors. We present results for optical spectra where the effects of the macroscopic local-field and microscopic exchange-correlation interaction are included beyond diagonal and random-phase approximation. Quasiparticle corrections to the single-particle energies have been added in the polarization function. Numerical calculations are performed for the column-IV materials Si, SiC, and diamond as model substances.

Photoluminescence (PL) properties of microwave-assisted chemical-vapor- deposition (CVD) diamond have been studied using ultraviolet synchrotron radiation. The defect-related 5RL PL feature, which was not detected in cathodoluminescence (CL), was observed for both undoped and boron-doped (200ppm) CVD diamond. The defect formation in the thin near- surface layer is discussed in relation to dependence of PL spectra on incident photon energy. In the case of boron-doped diamond, the boron-related peak was detected at 2.3eV while the band-A feature was not observed at 2.9eV. PL excitation (PLE) spectra associated with these emissions are also discussed in relation to absorption coefficients at energies above the band gap.

The effect of annealing in air on internal structure and optical properties of hot filament CVD nanocrystalline diamond films was investigated. Oxidation of the films lead to selective removal of intercrystallite layers with formation of highly porous structure with characteristic dimensions of several nanometers. Dramatic changes in optical transmission and Raman spectra were also observed. The origin of the two Raman spectrum maxima at 1140 and 500 cm−1 is discussed. Hydrogen absorption and desorption processes in porous diamond were studied.

6H silicon carbide (SiC) substrates were implanted with nitrogen and aluminum at different doses and annealed in the temperature range from 1300°C-1700°C. Micro-Raman Spectroscopy (μ-RS) measurements were performed in two sample geometries (conventional plane-view and cross-sectional). Changes of the polytype from 6H- to a cubic (SiC)1-xAIN)x, and influences in the 6H-SiC wafer up to depths of 2μm were detected. The results obtained by crosssectional μ-RS are discussed in comparison to other results from Reflection High Electron Energy Diffraction (RHEED), Rutherford Backscattering (RBS), Auger Electron Spectroscopy (AES), Transmission Electron Microscopy (TEM), and Positron Annihilation Spectroscopy (PAS) measurements.

Photoreflectance was used to study the optical properties of single crystal hexagonal GaN film on (0001) sapphire substrate grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined as 3.400 eV, and the possible origin of the PR signal was attributed to the modulation of the surface field and lineshape broadening of defects. Optical absorption and cathodoluminescence of the GaN sample were measured, and the optical absorption edge of 3.39 eV and the cathodoluminescence emission peak of 3.461 eV at low temperature (15.6K) confirmed the results of Photoreflectance.

Thermomodulation spectra from the metalorganic chemical vapor deposition (MOCVD) grown GaN have been measured in the temperature range 20 K - 310 K. A theoretical model is established to explain the modulation spectrum by considering the modulation of epilayer thickness and dielectric constant. By performing the lineshape analysis, the bandgap energy and broadening parameter were determined in the temperature range. The nonlinear temperature coefficient (Varshni coefficient) of energy gap is measured to be 5.9×10−4 eV/K. The temperature dependence of broadening parameter is also measured for the first time.

The optical properties of single crystal hexagonal GaN films grown on (0001) sapphire substrate by metalorganic chemical vapor deposition were investigated. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance, respectively. The refractive index of GaN as a function of photon energy was drawn from the transmission spectrum. Furthermore, Raman scattering spectra were employed to study the phonon modes of the GaN film. The properties of LO phononplasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.

In this paper, we reported experimental results about optical and structural properties of amorphous silicon carbide (α-Si1-xCx). The films of a-Si1-xCx) were grown by CVD on substrate of quartz glass. Optical constants (n-refractive index, a-absorption coefficient, Eg-optical energy band gap) of these films were determined by transmission spectra. The radial distribution functions (RDFs) of α- Sil−xCx) films were drawn out from the data of x-ray diffraction spectra. According to the RDFs, we imagined the statistic scene from which we could obtain the information of atomic radial distribution. The bond lengths and bond numbers of Si-Si, Si-C, and C-C could be also determined by RDFs. From the analysis of Raman spectra, we obtained the information of their vibration state density, and discerned the peaks of bond vibration, which agreed well with the results of α-Si1-xCx) RDF.

Photovoltaic effects in ultraviolet photoemission spectroscopy of the in-situ “rehydrogenated”, and reconstructed (111) diamond surfaces are evaluated. We show that photovoltaic charging effects during photoemission studies of the in-situ “re-hydrogenated” (111)-(l×l):H diamond surface are significant at temperatures as high as room temperature. In contrast, experiments on the reconstructed (111 )-(2×l) diamond surface find no photovoltaic charging which suggests that the surface exhibits relatively high conductivity (effectively grounded surface). These results demonstrate that extra care should be taken in determining the Fermi level pinning position relative to the bands at diamond surfaces and interfaces. The assumption that the UPS photoelectron spectra reflect the equilibrium energy band arrangement should be experimentally confirmed in each case, especially when wide band gap materials are involved.

The field emission current from boron doped polycrystalline diamond films was characterized as a function of voltage and temperature. The motivation for the current-temperature measurements was to assess the thermal stability of the diamond emitters and gain some insight into a possible emission mechanism.

Results from the current-temperature (I-T) measurements found that the field emission current appeared independent of temperature. The best characterization of the results implied a temperature independent electron tunneling mechanism if not electron emission from the valence band of diamond.

The near band gap photoelectric emission and field emission properties of diamond are investigated. Our results find three characteristic photoelectric yield spectra which have been observed from both polycrystalline CVD diamond films and single crystal diamond. The categories correspond to differences in bulk doping/surface preparation and illustrate the importance of band bending at the surface. Field emission experiments also find that the same three categories have distinct field emission properties. Our field emission observations are discussed in terms of electron transport properties from the bulk to the surface.