Boron Nitride (BN) thin films are deposited on heated (650 °C ) silicon (100) substrates using Nd:YAG (532 nm) and KrF excimer (248 nm) laser ablation. The laser beam is focused on the hBN targets. The films are grown using a laser repetition rate of 10 Hz atenergy density 3.8 J/cm2. Argon gas is mixed with the reactant nitrogen gas and the total gas pressure in the chamber during deposition is 20 Pa. Auger Electron Spectroscopy shows that the N/B composition ratio depends on the mixture ratio of nitrogen and the relativeemission intensity of B + (345.1 nm). The surface morphology of the films prepared by the 532 nm laser is rough with large particulates, whereas much smoother surfaces with fewer and smaller particulates are obtained with the 248 nm laser. Fourier Transform IR measurement shows that the cBN phase in the films is enhanced by applying the negative RF self-bias voltage ( ˜ 200 V) on the substrate electrode.

Gallium nitride and its alloys are the most promising materials for short wave light emitters. If high quality GaN single crystals can be prepared, the GaN base light emitters should be fabricated directly on the lattice-matched GaN substrate.

In this work, GaN crystals in nano and micro scale with definite faces have been prepared by dc arc discharge using gallium and N2+NH3 as starting materials. Transmission electron microscope, selected area diffraction, x-ray microanalysis of energy dispersive spectroscopy, and x-ray diffraction investigation of the as grown GaN crystals show that the well faceted crystals are single crystalline GaN in wurtzite structure having lattice constants a0=3.18Å and c0=5.18Å. The crystal size of stoichoimetric GaN in wurtzite structure depends on the partial pressure of nitrogen in the plasma. The maximum crystal size in this work is about several micrometers.

We have grown silicon carbide (SiC) on ultrathin Si (about 300Å) and on thick Si (about 2000Å) on commercial SIMOX (from IBIS Corp and SOITEC, Inc.), and bulk Si. Electron diffraction and Rutherford backscattering spectroscopy (RBS)/channeling studies indicate epitaxial growth of singlecrystal β-SiC even at growth temperatures as low as 1100°C.

We have already demonstrated the fabrication of ultrathin Si, as thin as 140Å on SiO2 by using the low-energy SIMOX (LES) (20 to 30 keV) process to produce films of lower cost and excellent integrity compared to thinned commercial SIMOX. Based on these results, ultrathin Si-on-insulator (SOI) substrates appear to have great potential for device quality SiC films. However, the carbonization and/or growth of SiC on ultrathin Si requires further optimization because the processes for surface cleaning and growth of SiC on bulk Si substrates cannot be applied because of the thinness of the substrate layers. Additional carbonization work at higher temperatures has indicated the possibility of converting the entire Si top layer.

Hot filament chemical vapor deposition (HFCVD) was utilized to grow high quality diamond film on porous silicon (PS) substrates to a thickness of 5–6 μm. Boron-doped silicon substrates of <100> orientation and resistivity of 5–15 ohm-cm were anodized by the electrochemical process to form PS. A slurry of diamond paste (1/4 micron average grain size) was rubbed on the samples for a few seconds before introduction into the chamber. Diamond film growth on the PS has the advantages of shorter incubation time and higher nucleation density as evident from scanning electron microscopy (SEM). The results of X-ray diffraction confirm the growth of predominatly (111) oriented high quality diamond film. Electrical properties were also studied by sputtering circular gold contacts on top of diamond film and measuring current-voltage (I-V) characteristics.

A density-functional theory based nonorthogonal tight-binding scheme is used to investigate the nonpolar surfaces of GaN in the wurtzite and zinc-blende phases. In III-V semiconductors the nonpolar surfaces mainly reconstruct by a bond-length conserving rotation of the surface atoms. In contrast to that for all nonpolar GaN surfaces this bond-length is shortened by ≈3 − 4%. We furthermore find the rotation angle to be significantly smaller than could be expected from results for GaAs and GaP.

We present a detailed investigation of β-SiC (100) surface reconstructions. Minimal energy configurations at both C- and Si-terminations are determined by using a density-functional based molecular-dynamics method. We provide information on the energetic order of various metastable surfaces and describe the geometrical details. In addition, we also study Si- and C-enriched configurations.

Boron-doped homoepitaxial diamond films were grown on natural diamond (001) substrates using microwave-assisted plasma chemical vapor deposition techniques. The surface structures were investigated using scanning tunneling microscopy (STM). This showed a dimertype 2×1 reconstruction structure with single-layer steps where dimer rows on the upper terrace are normal to or parallel to the step edges. We found that dimer rows parallel to the step edges are much longer than those normal to the step edges. The nearly single-domain surface structure observed by STM is in agreement with the low-energy electron diffraction (LEED) patterns from these surfaces. The high atomic resolution STM image showed that the local 1×1 configurations exist.

We have performed molecular dynamics simulations of adatom diffusion on the SiC(001) surface and found that the barriers for carbon adatoms is less than that for silicon adatoms. The diffusion paths were also found to be temperature dependent and at high temperatures the adatom diffusion constant was found to of the order of 10−5 cm2 s−1.

The use of trimethylgallium-trimethylamine (TMG:TMN) adduct as alternative cation precursor for MOVPE of GaN was studied by means of in-situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase: epitaxy (MOVPE) of GaN. Dynamic changes in the mass spectra are reported for the gas phase reactions between trimethylgallium (TMG) and TMN in hydrogen (H2/D2) and ammonia (NH3/ND3) ambients. Evidence presented for the high temperature TMG:TMN adduct formation, followed by ethane elimination. The strength of the adduct bonding is comparable to that of TMG:NH3 and thus suppresses TMN displacement by ammonia. The thermal stability of TMG:TMN was found to be higher in ammonia ambient than it is in hydrogen. Kinetic parameters for some of the decomposition processes are given.

Buffer layers promote lateral growth of films due to a decrease in interfacial free energy between the film and substrate, and large 2-dimensional nucleation. Smooth surfaces of thebuffer layers are desired. Optimum conditions for GaN-buffer growth on the vicinal surface of 6H-SiC(0001) were determined by atomic force microscope (AFM). AFM analysis of the GaN nucleation layers led to an optimum growth conditions of the GaN-buffer layer which was confirmed by cross-sectional transmission electron microscopy, Hall measurements and photoluminescence spectra. Optimum growth conditions for GaN-buffer layer on SiC(0001) was determined to be 1 minute growing at 550°C.

Transmission electron microscopy (TEM) was used to investigate the interfacial microstructures and phases involved in the nucleation and growth of the oriented diamond on Ni substrates by a multi-step growth process. A molten surface layer is formed during the process, which appears to be critical for both promotion of the diamond nucleation and suppression of graphite formation. Cross-section TEM analysis revealed that a polycrystalline nickel carbide interfacial structure exists between the diamond particles and the single crystal Ni substrate. X-ray diffraction analysis (XRD) identified the carbide phase as Ni4C. It is suggested that the Ni4C is formed in the molten layer and stabilizes sp3C precursor for diamond nucleation.

The results of extensive theoretical studies of group IV impurities and surface and interface properties of nitrides are presented and compared with available experimental data. Among the impurities, we have considered substitutional C, Si, and Ge. CN is a very shallow acceptor, and thus a promising p-type dopant. Both Si and Ge are excellent donors in GaN. However, in AlGaN alloys the DX configurations are stable for a sufficiently high Al content, which quenches the doping efficiency. At high concentrations, it is energetically favorable for group IV impurities to form nearest-neighbor Xcation-XN pairs. Turning to surfaces, AIN is known to exhibit NEA. We find that the NEA property depends sensitively on surface reconstruction and termination. At interfaces, the strain effects on the band offsets range from 20% to 40%, depending on the substrate. The AIN/GaN/InN interfaces are all of type I, while the A10.5Ga0.5 N/A1N zinc-blende (001) interface may be of type II. Further, the calculated bulk polarizations in wurtzite AIN and GaN are -1.2 and -0.45 μC/cm2, respectively, and the interface contribution to the polarization in the GaN/AlN wurtzite multi-quantum-well is small.

Microstructure and extended defects in α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AIN (or GaN) buffer layers have been studied using transmission electron microscopy. The types and distribution of extended defects were correlated with the film growth mode and the layer nucleation mechanism which was characterized by scanning force microscopy. The nature of the extended defects was directly related to the initial three-dimensional growth. It was found that inhomogeneous nucleation leads to a grain-like structure in the buffer; the GaN films then have a columnar structure with a high density of straight edge dislocations at grain boundaries which are less likely to be suppressed by common annihilation mechanisms. Layer-by-layer growth proceeds in many individual islands which is evidenced by the observation of hexagonal growth hillocks. Each growth hillock has an open-core screw dislocation at its center which emits monolayer-height spiral steps.

The influence of Si doping on the structure of GaN grown by metal-organic chemicalvapor deposition (MOCVD) has been studied using transmission electron microscopy (TEM), x-ray diffraction and Raman spectroscopy. Undoped and low Si doped samples were compared with samples of increased dopant concentration. In addition, defect reduction due to different buffer layers (AIN and GaN) is discussed. Silicon doping improves surface morphology and influences threading dislocation arrangement. High doping leads to a more random distribution of dislocations. Based on this study it appears (for the same dopant concentration) that an AIN buffer layer can significantly reduce the number of threading dislocations, leaving the samples more strained. However, no significant reduction of threading dislocations could be observed in the samples with GaN buffer layer. These samples are the least strained.

CVD diamond films with nitrogen content varying from 10 ppm to 132 ppm have been studied by electron spin resonance (ESR), light-induced ESR (LESR) as well as spin-dependent conductivity (SDC). Two characteristic signals have been observed. A carbon-related defect line with g = 2.0029 ± 0.0002 and width 4 ± 1 G, is observed in ESR, LESR and SDC. The intensity of this line measured by ESR increases linearly with nitrogen content. For low-defect-density samples, or after illuminating the high-defect-density samples with UV light, a second signal is observed both in ESR and LESR, but not in SDC, with a central line at g = 2.0024 ± 0.001 and width 0.2 ± 0.1 G and related hyperfine satellites ≈30 G away from the central line. This line is assigned to isolated substitutional nitrogen, the so-called P1 center. The density of N-related paramagnetic states is strongly affected by illumination and heat treatments. Spin-dependent conductivity measurements show that the dark conductivity at room temperature in CVD-diamond is dominated by hopping at the g = 2.0029 defects.

Diamond thin films have been deposited on silicon substrates by hot-filament chemical vapor deposition (HF-CVD). Substrate temperature and methane concentration have been varied and the resulting structural properties of the deposited films studied. Raman spectroscopy, scanning electron microscopy and electron paramagnetic resonance (EPR) measurements were performed. The EPR measurements showed a single spectrum at g = 2.0027(2). The bulk concentration of the paramagnetic species, as determined from the total EPR absorption were found to vary in the range 1017 to 1019 cm−3. Low paramagnetic defect concentrations were found for samples exhibiting a low non-diamond carbon contribution to the Raman spectrum. These samples were those grown with a methane concentration of I % or less.

Hall effect, deep level transient spectroscopy, optical absorption, and optical admittance spectroscopy were employed to determine the position of the vanadium acceptor and vanadiumnitrogen complex in vanadium- and nitrogen-doped 4H and 6H SiC. Hall effect results indicate that the acceptor position in 4H(6H) SiC is 0.80(0.66) eV beneath the conduction band edge. The DLTS signature of the defect in the 4H polytype showed an ionization energy of 806 meV and a capture cross section of 1.8×10−16 cmr−2 The optical absorption measurements proved that the acceptor level investigated is related to isolated vanadium, and therefore the vanadium acceptor level. Based upon DLTS and SIMS measurements, the maximum solubility of vanadium in SiC was determined to the 3×10−17 crn3. An examination of polarized light experiments indicates that vanadium also complexes with another element to form electronic(at 5000 cm−1) and vibrational absorption(at 683 cm−1) bands. While the other constituent cannot be identified, evidence suggests that nitrogen is a likely candidate. This complex introduces a deep level at Ec−0.78 eV as determined using optical admittance spectroscopy.

We have calculated the electron mobilities in GaN and InN taking into consideration scattering by short range potentials, in addition to all standard scattering mechanisms. These potentials are produced by the native defects which are responsible for the high electron concentrations in nominally undoped nitrides. Comparison of the calculated mobilities with experimental data shows that scattering by short range potentials is the dominant mechanism limiting the electron mobilities in unintentionally doped nitrides with large electron concentrations. In the case of AlxGal1−xN alloys, the reduction in the electron concentration due to the upward shift of the conduction band relative to the native defect level can account for the experimentally measured mobilities. Resonant scattering is shown to be important when the defect and Fermi levels are close in energy.

Electrically active defects in both 4H and 6H polytypes of SiC have been observed through the use of deep level transient spectroscopy (DLTS). Schottky contacts were grown by vapor phase epitaxy (VPE) with doping concentrations, the epitaxial layer having a doping concentration in the range of 1014 cm−3 to 1017cm−3. Numerous levels have been found in the as-grown n-type 6H-SiC samples and secondary ion mass spectrometry (SIMS) and MeV electron irradiation have been employed to corrrelate the defect levels to impurities or structural defects. In contrast, only a single level is observed in the as-grown 4H-SiC samples.

Deep level defects in Mg compensated GaN grown by metal-organic vapor phase epitaxy were investigated using photocapacitance spectroscopy measurements on Schottky barrier diodes. Addition of magnesium resulted in the formation of a series of deep centers with optical threshold energies of 1.0, 1.2, 1.8, and 3.1 eV. Upon annealing the epitaxial GCN in nitrogen at 850°C the ind-gap levels disappeared and only the trapping level at 3.1 eV remained. The mid-gap levels are ascribed to Mg dopant complexes which may in part be responsible for low doping efficiency of Mg in the as-grown, doped GaN. The deep level at 3.1 eV commonly observed from all Mgdoped GaN most likely involves the Mg acceptor. The photo-excited state of the 3.1 eV level had relaxation times of the order of 103 sec at 295 K.