We studied by deep level transient spectroscopy (DLTS) and capacitance-voltage (CV) measurements the effects of doping (Zn, S), nitrogen implantation and annealing of n-type GaN grown on sapphire by MOVPE. The DLTS spectra of the as grown samples show two defect levels which are assumed to be identical with recently reported levels [10, 11]. In N-implanted GaN a third level is introduced which is not detectable in our as grown samples. This levels concentration follows the increasing N-implantation density. The depth profiles of its concentration correlate with the distribution of implantation defects expected from Monte-Carlo simulation. After annealing at 900°C for 60s the additional defect level vanishes. The DLTS spectrum then resembles those of annealed as grown samples. The n-type carrier concentration (CV measurements) increases in samples with low N-implantation dose. This implantation effect can be removed also with the RTA step. The increasing carrier concentration provides evidence that the N vacancy is a donor in GaN. For Zn and S doped GaN deep defect levels has been found, which are reported here.

The growth surface of a 6H-SiC boule, grown by physical vapor transport, was examined using scanning force microscopy. The dimensions of surface/micropipe intersections and screw dislocation Burgers vectors have been determined from topographic data. All micropipes are positioned along the lines of super screw dislocations with a Burgers vectors of at least 4 times the c-axis repeat distance (15.2 Å). Perfect c-axis screw dislocations with Burgers vectors of only 15.2 Å are stable and do not have open cores. Measurements show that micropipe core radii, determined indirectly from the width of the craters formed at the surface/micropipe intersections, increase with the square of the dislocation Burgers vector.

Defect structures in (111) 3C-SiC single crystals, grown using the Baikov technique, have been studied using Synchrotron White Beam X-ray Topography (SWBXT). The major types of defects include complex growth sector boundary structures, double positioning twins, stacking faults on { 111 } planes, inclusions and dislocations (including growth dislocations and partial dislocations bounding stacking faults). Detailed stacking fault and double positioning twin configurations are determined using a combination of Nomarski interference microscopy, SEM and white beam x-ray topography in both transmission and reflection geometries. Possible defect generation phenomena are discussed.

Steps at the AIN/SiC interface have been investigated by HREM. Some of them do not introduce any defects. Others steps present a dislocation character which can contribute to relieve the strain due to the lattice mismatch. A third kind of steps gives rise to a prismatic planar fault for which a model is given. A reaction between prismatic and basal stacking faults is analyzed.

In some materials, Van der Merwe's equilibrium theory of strain relief is believed to explain the sudden transition from pseudomorphic growth of a thin film to a progressively relaxed state. We show, for the first time for GaN, how an accurate estimate of the critical thickness of a thin film can be extrapolated from suitable measurements of lattice constants as a function of film thickness using synchrotron X-ray. We do this both for an elementary elastic energy function, in which the interactions between the dislocations are ignored, and for a more realistic energy estimate due to Kasper. The method is found to work quantitatively for thin films of GaN on AIN. The critical thickness is determined to be 29 ± 4 Å.

Comparisons between the wetting characteristics of (0001)si 6H-SiC and (111) Si surfaces in various acids and bases were made. It was found that 10:1 HF dipped Si (111) surfaces were hydrophobic where as the (0001)si 6H-SiC surfaces were hydrophilic. (0001)si 6H-SiC surfaces capped with a 20Å Si layer, however, were hydrophobic after HF dipping and exhibited outgassing levels on annealing which were several orders of magnitude lower than SiC wafers dipped in HF without the capping layer. Annealing the Si capped (0001)si 6H-SiC surfaces in UHV at 1100°C for 5 min. was found to be sufficient to thermally desorb the Si capping layer and produce a (3×3) Si rich, oxygen free (0001)si 6H-SiC surface.

The surface stoichiometry, surface morphology and electrical conductivity of AIN, GaN, InN, InGaN and InAIN was examined at rapid thermal annealing temperatures up to 1150 °C. The sheet resistance of the AIN dropped steadily with annealing, but the surface showed signs of roughening only above 1000 °C. Auger Electron Spectroscopy (AES) analysis showed little change in the surface stoichiometry even at 1150 °C. GaN root mean square (RMS) surface roughness showed an overall improvement with annealing, but the surface became pitted at 1000 °C, at which point the sheet resistance also dropped by several orders of magnitude, and AES confirmed a loss of N from the surface. The InN surface had roughened considerably even at 650 °C, and scanning electron microscopy (SEM) showed significant degradation. In contrast to the binary nitrides the sheet resistance of InAIN was found to increase by ˜ 102 from the as grown value after annealing at 800 °C and then remain constant up to 1000 °C, while that of InGaN increased rapidly above 700 °C. The RMS roughness increased above 800 °C and 700 °C respectively for InAIN and InGaN samples. In droplets began to form on the surface at 900 °C for InAIN and at 800 °C for InGaN, and then evaporate at 1000 °C leaving pits. AES analysis showed a decrease in the N concentration in the top 500 Å of the sample for annealing ≥800 °C in both materials.

Crystals of cubic silicon carbide (3C-SiC) were grown in an RF-induction furnace on graphite substrates by atmospheric pressure chemical vapor deposition (APCVD) from a single precursor, methyltrichlorosilane (MTS) in hydrogen. The deposits were characterized by micro-Raman spectroscopy, x-ray diffraction, and atomic force and scanning electron microscopies. Above ˜1600°C preferential 〈110〉 growth directions were identified for the majority of the crystals. At intermediate deposition temperatures (1600–1700°C) the dominant morphology consisted of yellow prismatic crystals heavily twinned along {111 }and {111} At substrate temperatures exceeding ˜1750°C hexagonally-shaped {1111} oriented 3C-SiC platelets were formed with alternating {001 }/{ 101} edges. The dependence of nucleation density, film morphology and film orientation on deposition conditions will be discussed with emphasis on the growth of high quality single crystals of 3C-SiC.

The dopant incorporation efficiencies of SiC bulk single crystals were investigated by the measurement of optical absorption coefficients and chemical analysis by Glow Discharge Mass Spectroscopy. The SiC crystals were grown on the seed with the {1100} face by a sublimation method. The grown ingot consisted of approximately three parts, which were the regions grown with the {1100} face (I), the {110n} face (II) and the {110n} face (III) as a growing front. The nitrogen concentrations in these parts were in the order of II>I>III. The wafers exhibited the color distributions in the c-plane due to the difference of the growing facet. The nitrogen incorporation efficiencies were discussed in terms of atomic structure on the surface. The aluminum concentration in the crystal grown on a {1100}-faced seed was in the medium between those in crystals grown on Si-face and C-face. On the other hand, the boron concentration was similar to that of Si-face grown crystal, and higher than that of C-face grown crystal.

Hot-filament chemical vapor deposited (HFCVD) boron doped polycrystalline diamond thin films having low volume resistivity were grown on sapphire. The films were characterized using scanning electron microscope (SEM), X-ray diffraction, and current-voltage measurements. SEM micrographs show good crystalline structure with preferred (100) orientation normal to the surface of the film. X-ray diffraction pattern revealed diamond characteristics with the four typical diamond peaks present. Finally, the obtained I-V characteristics indicated that the film's volume resistivity is at least two orders of magnitude lower than those of HFCVD polycrystalline diamond thin films grown on silicon under similar growth conditions.

The activation of acceptors was investigated for Mg-doped, heteroepitaxial layers of GaN grown by metalorganic chemical vapor deposition. After growth the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500°C to 775°C. The samples were studied by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy in the as-grown condition and after each temperature step. The thermal treatment leads to the formation of acceptors which are characterized by an activation energy for ionization in the range between 165 meV and 182 meV. These acceptors are attributed to Mg atoms substituting for Ga in the GaN lattice. The experimental results for the acceptor activation are consistent with the dissociation of electrically inactive acceptor-hydrogen complexes. The reversibility of this process is investigated by the exposure of the activated, p-type GaN samples to atomic hydrogen in a remote-plasma hydrogenation system at 600°C and reactivating at 850°C.

We have applied frequency-dependent capacitance measurements and admittance spectroscopy on metalorganic vapor phase epitaxy GaN:Mg to study the electronic states associated with Mg doping. Samples with different Mg doping levels were grown and annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. After a 800 °C anneal, frequency-dependent measurements show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high frequency modulation. The net ionized acceptor concentrations was found to be greater at a higher Mg doping level. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of at least one impurity-related acceptor level with an activation energy of ∼ 140 meV. A reduction in the annealing temperature was found to lead to a lower net ionized acceptor concentration, as well as a higher activation energy.

Hydrogen plasma passivation effects are studied for undoped AlGaN layers grown by MOCVD. Hydrogen treatment at 200°C for lh led to a substantial decrease in carrier concentration accompanied by an increase in electron mobility. The magnitude of the near-band edge absorption tails also dramatically decreased after hydrogen passivation. The effect is explained by pairing of negatively charged hydrogen acceptors with positively charged native donors commonly believed to be related to nitrogen vacancies. The bond strength in such hydrogen complexes increases as the composition of AlGaN moves towards AIN, as revealed by results of post hydrogenation annealing.

Preliminary results of theoretical studies of hydrogen and hydrogen-related defects in cubic GaN are reported. Our calculations contrast with those of other authors in that the host crystal is represented by molecular clusters rather than periodic supercells, and that they are obtained using an all-electron methodology rather than the single effectiveparticle approach of density-functional theory. Our results confirm some predictions of other authors but conflict with others.

We have calculated electronic structure, energetics and migration for hydrogen and hydrogen complexes in GaN employing state-of-the-art first-principles calculations. Using these results in combination with previous detailed investigations about native defects we have calculated the concentration of hydrogen and dopants for different growth conditions. Our results reveal a fundamental difference in the behavior of hydrogen in p-type and n-type material. In particular, we explain why hydrogen has little effect on donor impurities and why H concentrations are low in n-type GaN. We discuss why hydrogen is beneficial for acceptor incorporation in GaN, and identify the limitations of this process.

6H polytype silicon carbide (SiC) samples of n-type have been implanted with 50 keV H+ ions and subsequently annealed at temperatures between 200 °C and 1150 °C. Using depth profiling by secondary ion mass spectrometry motion of hydrogen is observed in the implanted region for temperatures above 700 °C. A diffusion coefficient of ∼10−14 cm2/s is extracted at 800°C with an approximate activation energy of ∼3.5 eV. Hydrogen displays strong interaction with the implantation-induced defects and stable hydrogen-defect complexes are formed. These complexes anneal out at temperatures in excess of 900°C and are tentatively identified as Carbon-Hydrogen centers at a Si vacancy.

Beryllium (Be), magnesium (Mg) and silicon (Si) impurities in zinc-blende galliumnitride (c-GaN) are investigated by the tight binding-linear combination muffin-tin orbitals (TBLMTO) method using a 64-atom supercell. Be and Mg impurities at a Ga site, respectively induce partially empty acceptor-like bands at the valence band edge, which result in p-type conductivity of doped c-GaN. Si impurity in the Ga sublattice creates a partially occupied impurity subband overlapping with the conduction band edge and is responsible for the measured n-type conductivity. The impurity levels of a Si at a N site are located deep in the gap and do not influence much the conductivity of c-GaN. The shell-projected, total and partial densities of states and the charge density maps are used to elucidate the energy and spatial localizations of the impurity states

Impurity conduction (or hopping conduction) has been observed in the more heavily n-type 4H-SiC samples by both temperature dependent resistivity measurements and thermal admittance spectroscopy. The measured activation energies ɛ 3 for hopping were 4–5 meV and 2.3–3.0 meV respectively. No evidence of hopping conduction was seen by either method in the sample where ND-NA < 1018 cm-3. The thermal admittance spectrum of the lightly n-type sample showed the two nitrogen levels at 53 and 100 meV.

Epitaxial layers of A1xGa1-xN were grown by MOCVD on sapphire substrates and characterized by temperature dependent Hall effect, optical absorption, SIMS and photoluminescence. The concentration of native donors was found to decrease with increase of growth temperature. Deep levels found in A1GaN layers were interpreted as A1 double donor state and T2 donor state of nitrogen vacancy.

Four CVD diamond films grown on tungsten carbide were used for diffusion. Diffusion was performed in a hydrogen atmosphere. Three methods of diffusion were used: conventional diffusion due to concentration gradient, forced diffusion under a dc electric bias with thermal ionization and forced diffusion with optical and thermal ionization of boron acceptor level in diamond. The temperature dependence of the electrical conductivity of the diffused samples was measured in the temperature range 300–600 K. The increase of approximately six order of magnitude in conductivity of the films doped by forced diffusion was obtained. The samples diffused with boron by conventional diffusion due to concentration gradient showed only one order of magnitude increase in electrical conductivity.