Room temperature Raman scattering measurements performed on undoped GaN films indicate that high crystalline quality wurtzite material has been deposited on the basal plane of sapphire. Photoluminescence study of these films show that thicker films (t > 4μm) are homogeneous along the growth direction. The PL spectra of Mg-doped films are dominated by an intense emission band around 3.1 eV associated with recombination processes involving donor-acceptor pairs.

Hydrogen incorporation during gas-phase growth of III-V nitrides is thought to play an important role in determining the apparent doping efficiency, due to unintentional passivation of dopants. Hydrogen implantation can also be used for electrical and optical isolation of neighboring devices, as in other lll-V materials such as GaAs. We have implanted 2H at 40 keV to doses of 5 × 1015 cm-2 at room temperature into epitaxial layers of GaN, AIN and InN grown by MOMBE on GaAs substrates, and measured the ion ranges and hydrogen redistribution upon subsequent furnace annealing. The hydrogen profiles remain unchanged for annealing temperatures up to 800–900°C for GaN and AIN, and 600° for InN. Samples were also deuterated from an ECR plasma at 250 or 400°C for 30 min, producing 2H incorporation depths of ≤ 1 μ in GaN. With annealing, there is no significant hydrogen redistribution observed at temperatures up 800°C. Hydrogen concentrations remain in the range ∼ 1019 cm-3 under these conditions. At 900°C considerable hydrogen outdiffusion to the surface occurs. The thermal stability of hydrogen in these III-V nitride films indicates the need for post-growth annealing at high temperatures to achieve appreciable doping efficiencies.

An infrared emission peak at 1.25 eV is observed from a GaN film which exhibits strong yellow luminescence peaking at 2.15 eV. It is most efficient at a temperature of 160 K. The full width at half maximum (FWHM) of the IR peak is 0.17±0.01 eV, which is about 1/3 that of the yellow peak.

This paper describes the trends in the electronic structure of diamond, silicon carbide, the group-Ill nitrides and some related materials. The relationships between the electronic band structures in the zincblende and wurtzite structures are adressed. For SiC, the discussion is extended to other poly types. The trends with ionicity and atomic number are explained. The purpose of this discussion is to help identify the similarities and differences between the various classes of wide bandgap semiconductors. The strain effects on the band structure are discussed and calculated elastic constants are given for SiC, GaN and AlN. Spectroscopie probes of the band structure such as pholoemission and UV-refiectivity are discussed for GaN and SiC. Materials with the formula II-IV-2 are proposed to be an interesting complement to the III-N's. In particular, BeCN2 is a direct gap semiconductor with elastic properties close to those of diamond and may also be useful as a bufferlayer for diamond growth.

Tunable second-harmonic (SH) transmission measurements were performed on a series of GaN films epitaxially deposited onto (OOOl)-oriented sapphire. Analysis of the nonlinear response showed an increase in the second-order nonlinear susceptibility (χ(2)ijk) when the photon energy of the SH field was tuned above the absorption edge in each respective film. Specifically, the magnitude of the χ(2)zxx element in χ(2)ijk reached a maximum of 0.5 × 10-7 e.s.u. just above the the fundamental bandgap with a dispersion similar to the predicted nonlinear response in wide-bandgap cubic zincblende II-VI semiconductors such as ZnSe.

The electrical properties associated with diamond charged particle- and photo-detectors were studied using charged particle-induced conductivity (CPIC) and photo-induced conductivity (PIC). The collection distance d, the product of the excess carrier mobility μ excess carrier lifetime T and electric field E, was used to characterize the diamonds. X-ray diffraction, Raman spectroscopy, photoluminescence, SEM and TEM were performed on CVD diamond detectors to investigate the limitations of the electrical properties. Correlations were found between the electrical properties and the material characterizations.

A measure of the electron mobility anisotropy in n-type 4H and 6H-SiC has been obtained using the Hall effect over the temperature range 80K<T<600K. Hall mobility and resistivity data are collected from appropriately oriented bar patterns fabricated into high quality epitaxial material grown on (1100) or (1120)surfaces having total impurity concentrations 1017-1018 cm-3. The observed mobility ratio for 4H is μ[1120]/[0001] and is independent of temperature. For 6H, the ratio μ[1100]/[0001] decreases from ∼6.2 at 80K to ∼5.0 at 150K and is essentially constant (∼4.8) above 200K. A donor level near 0.6 eV is occasionally observed in 4H which reduces the high temperature electron mobility and introduces an apparent temperature dependence to the mobility ratio if nonuniformly distributed.

The diffusion of oxygen, lithium, chlorine, and fluorine in CVD diamond films was performed under bias at 700 and 1000 °C. SIMS and Auger analyses were used to determine the impurity concentration. After diffusion, the concentrations of Li and O in the diamond films were found to be of the order of (3–4)×1019 cm-3. The fluorine concentration was of order of (l-2)×1017 cm-3. The conductivity was p-type. The change in the resistivity due to diffusion was nearly nine orders of magnitude for the sample diffused under electric field, and six orders of magnitude for the samples diffused without field. No dependence of the impurity concentration on the applied bias was observed except for fluorine. The fluorine concentration dependence on the electric field indicates that fluorine may have formed a shallow level in the diamond band gap. The fact that large concentrations of impurities can be diffused into diamond films at relatively low temperatures indicates the presence in the films of many lattice defects (including grain boundaries).

The valence-band offset at the zincblende AIN/GaN. AIN/InN and InN/GaN (110) interfaces are calculated self-consistently by means of the linear muffin-tin orbital method using up to 5+5 layer supercells. All interfaces have a type I-offset. Assuming interface orientation and polytype effects on the valence-band maximum to be reasonably small, a type I offset can also be expected for wurtzite interfaces. Our results are in very good agreement with experimental values for AIN/GaN, the only nitride interface for which they are available.

Subject index terms: band offsets, interfaces, hetero junctions, superlattices. III-nitrides.

Complex formation at indium and cadmium impurities implanted into samples of 3C-, 4H-and 6H- SiC was investigated by means of Perturbed Angular Correlation (PAC)-Spectroscopy. After annealing at 1600 K up to five different configurations characterized by their specific electric field gradients (EFG(i)) were observed in 6H- SiC, only four complexes in 4H- SiC; in the 3C- modification no complex was observed. All EFG's are axially symmetric and are oriented along the c- axis of the crystal. In a highly nitrogen doped 6H- SiC epi- layer an new EFG was observed. It is tentatively assigned to a close indium- nitrogen pair.

Time resolved photoluminescence and optically detected magnetic resonance experiments were performed on the 2.985 eV (N3) luminescence band in natural diamond and the 2.964 eV luminescence center in synthetic diamonds. For the N3 luminescence the resonance occurs in the 2E excited state of the center. On the 2.964 eV luminescence a strongly anisotropie resonance signal is observed. The frequency response of the magnetic resonance signals confirms the time resolved photoluminescence measurements.

Diamonds grown by the temperature gradient method using a nickel catalyst show an optical absorption band, extending from 2.5 eV to 2.56 eV, with a zero-phonon line at 2.51 eV. At 4 K this line exhibits fine structure; it is made up of 3 components at 2.509 eV, 2.510 eV and 2.511 eV. In absorption the fine structure components have the same relative intensity at different temperatures. We report on the effects of uniaxial stress on the zero-phonon transition at 77 K. We propose an interpretation of the results according to which the optical defect has a tetrahedral symmetry, and the 2.51 eV line occurs between two T2 states.

Free carrier absorption (FCA) in n-type 6H-SiC doped with nitrogen has been studied in the energy range 50–250 cm-1 using samples of different free carrier concentrations ranging from 2.0–1016cm-3 to 7.0–1017cm-3. The index of wave number dependence of FCA p varies between -1.4 and -0.55 depending on free carrier concentration and electron mobility. The experimental results are in good agreement with the classical expression for the FCA coefficient. Quantum mechanical expressions for the FCA coefficient do not reproduce the measured p values. It is supposed that this is due to fact that the requirement for the application of perturbation theory ΩT ≫ 1 is not fulfilled. We investigated the anisotropy of FCA with respect to the c-axis and find a strong difference between ∝ ┴ and ∝∥.

Aluminum nitride (AlN) films were grown on silicon (Si) substrates by chemical vapor deposition (CVD). The films were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The refractive index of the AlN films was determined by ellipsometry. Current-voltage and current-temperature characteristics were performed on metal-AlN-p+ Si structures with Pt, Au and Al as metal electrodes. The characteristics showed that at high field and high temperature the carrier conduction mechanism in the film was dominated by Frenkel-Poole emission. The relative dielectric constant of the AlN films was estimated to be 9.66+0.3 from capacitance-voltage-frequency (C-V-f) measurements on Au-AlN-p+ Si.

The content of bonded hydrogen in hot filament grown diamond films was determined by Fourier transform Infrared (FTIR) measurements before and after annealing. The quantity of bonded hydrogen was found to remain unchanged on annealing in diamond films with high amounts of microcrystalline diamond and amorphous carbon. The hydrogen content was found to decrease on annealing ∼9 times in diamond film of good crystalline quality. The change of the bulk hydrogen content did not seem to be linked to changes in resistivity of the samples.

A novel method has been developed to prepare highly conductive and wide band gap doped (B2H6/PH3) microcrystalline silicon carbide (μ-SiC) by excimer (ArF) laser crystallisation. Doped a-SiC:H films were prepared by Plasma Enhanced Chemical Vapour Deposition (PECVD), both with and without H2 dilution. After crystallisation, this material has Taue gap of around 2.0 eV and exhibits a dark conductivity as high as 20 (Ωcm)-1, more than ten orders of magnitude higher than before the laser irradiation. This is shown to be mainly due to the formation of SiC microcrystallites in the laser crystallised a-SiC:H.

In this paper, we report that this material can be utilised not only as the carrier injection layer in a-SiC:H based Thin Film Light Emitting Diodes (TFLEDs) but also as a luminescent layer. Blue light emission has been observed from a laser crystallised (LC) doped μc-SiC based electroluminescent device, the peak wavelength is around 490nm.

The simplicity of excimer (ArF) laser crystallisation and its capability to fabricate poly-Si TFTs, makes this a promising novel method to realise fully integrated Si large area multi-colour displays.

The effects of friction and wear were examined on plasma enhanced chemical vapor deposition (PECVD) diamond films deposited on tungsten substrates. The tribology of diamond on diamond was studied and the changes in surface roughness and the bearing ratio were determined before and after wear. The (111) textured heteroepitaxial films were studied morphologically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The changes in morphology involved a transition from the large as grown diamond crystallites with a mean diameter of 10 μm to a surface with grains as small as 100 nm. The nature of the wear-modified films will be discussed regarding the possible mechanisms for the surface changes.

Work partially supported by NASA Lewis Research Center grant NAG3–1430.

Micro- and Macro-photoluminescence techniques were employed in this research to investigate the role of nitrogen-doping on the optical spectra of chemical vapor deposited diamond films and to determine whether the origin of the broadband luminescence is due to vibronic interaction of the nitrogen centers. The temperature behavior of the broadband PL and of the 1.681 eV silicon related optical center were analyzed. The intensity of the broadband was found to exhibit a temperature dependence characteristic of optical emission from a continuous distribution of gap states while the temperature dependence of the 1.681 eV band followed the Boltzmann quenching process.

The X-band ESR of thin diamond films deposited from 99.5% H2/0.5% CH4 is compared to that of films similarly prepared from D2CD4 and H2/13CH4. The main line and the satellites at ±7.2 G are unaffected by annealing at T <. 1100°C, but their intensity is reduced upon annealing at T ∼ 1200°C. As the satellites are absent from the deuterated films, they are attributed to newly identified dangling bond-H centers, either on internal microvoid surfaces or embedded in the tetrahedral network. This is consistent with the 13C spin-lattice relaxation rate, which indicates that the distribution of paramagnetic centers is homogeneous to within ∼0.04 μm. However, they may be nonuniformly distributed on a finer scale, consistent with the concentrations in m ulti vacancies or stacking faults recently suggested by Fanciulli and Moustakas.

The 1H and 13C nuclear magnetic resonance (NMR) of thin diamond films deposited from naturally abundant (1.1 at.%) as well as 50% and 100% 13C-enriched CH4 heavily diluted in H2is described and discussed. Less than 0.6 at.% of hydrogen is found in the films which contain crystallites up to ∼15 μm across. The 1H NMR consists of a broad 50–65 kHz wide Gaussian line attributed to H atoms bonded to carbon and covering the crystallite surfaces. A narrow Lorentzian line was only occasionally observed and found not to be intrinsic to the diamonds. The 13C NMR demonstrates that >99.5% of the C atoms reside in a quaternary diamond-like configuration. The 13C spin-lattice relaxation times T1 are four orders of magnitude shorter than in natural diamond and believed to be due to 13C spin diffusion to paramagnetic centers, presumably carbon dangling bonds. Analysis of T1 indicates that within the 13C spin diffusion length of ∼0.05 μm these centers are uniformly distributed in the diamond crystallites, possibly concentrated on the internal surfaces of a relatively dense system of nanovoids.