Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

We report recent results from the photometric follow-up study we are conducting in the context of the SAURON project. We use ground-based MDM V −band and Spitzer/IRAC 3.6 μm imaging to characterise our sample of E, S0 and Sa galaxies photometrically. Combined with SAURON integral-field spectroscopic observations, this information allows us to explore and understand the location of these galaxies on the Fundamental Plane relation, providing an important diagnostic tool to study their formation and evolution.

I. Construction for the Brocard points.

Let ABC be a triangle. Describe a circle touching AB in A and passing through C; draw the chord AP parallel to BC. Join BP meeting this circle in Ω

We investigate the well-known correlations between the dynamical mass-to-light ratio M/L and other global observables of elliptical (E) and lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates that dark matter in early-type galaxies contributes ~30% of the total mass inside one Re, in agreement with previous studies, with significant variations from galaxy to galaxy. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast rotating galaxies have lower dark matter fractions than the slow rotating and generally more massive ones.

Pendeo-epitaxy has been applied to nonpolar a-plane GaN layers in order to observe if such process will lead to defect reduction in comparison with direct growth on this plane. Uncoalesced and coalesced a-plane GaN layers with thicknesses 2μm and 12μm, respectively, have been studied by conventional and high resolution electron microscopy. The following structural defects have been observed in pendeo-epitaxial layers: (1) basal stacking faults, (2) threading dislocations, and (3) prismatic stacking faults. A drastic decrease in the density of threading dislocations and stacking faults was observed in ‘wing’ areas with respect to ‘seed’ areas. Cross-section images reveal cracks and voids at the areas where two coalesced wings meet each other. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the types I1, I2 and I3. The I3 type basal stacking fault, predicted theoretically, was observed experimentally for the first time.

Homoepitaxial films of 4H-SiC(1120) and 8° off-axis 4H-SiC(0001) have been grown and characterized. The number of domains and the range of full-width half-maxima values of the x-ray rocking curves of the [1120]-oriented wafers were smaller than the analogous values acquired from the (0001) materials. Hydrogen etching of the former surface for 5 and 30 minutes reduced the RMS roughness from 0.52 nm to 0.48 nm and to 0.28 nm, respectively; the RMS roughness for a 30 μm (1120) film was 0.52 nm. Micropipes in the substrates did not thread beyond the film-substrate interface. The separation distance between stacking faults was determined to be 10 μm by transmission electron microscopy. Hall mobilities and carrier concentrations of 12,200 cm2/Vs and 3.1×1014 cm−3 and 800 cm2/Vs and 7.4×1014 cm−3 were measured at 100°K and 300°K, respectively. Photoluminescence indicated high purity. 4H-SiC(1120) PiN devices exhibited average blocking voltages to 1344 V and a minimum average forward voltage drop of 3.94 V.

Crystalline damage created by ion-implantation of dopant impurities in ZnO (0001) substrates was characterized as a function of atomic mass of implanted species using triple-axis (2θ-ω/ω) x-ray diffraction and Rutherford backscattering (RBS). The former revealed the presence of implantation-induced strain through the broadening of the isometric and asymmetric 2θ-ω reflections. However, RBS indicated that the damage introduced during implantation of these ions was insufficient to transform the crystalline lattice into a completely amorphous state. Additional XRD characterization as a function of annealing temperature of the implanted materials showed a reduction in the broadening of the isometric reflections, indicating that structural recovery of implanted ZnO crystals can be achieved.

The band alignment of SiO2 and GaN is important for passivation of high voltage devices and for gate insulator applications. In this study XPS and UPS techniques are employed to determine the electronic states as SiO2 is deposited onto a clean GaN surface. The substrate was epitaxially grown n-type GaN on 6H-SiC (0001) substrates with an AlN (0001) buffer layer. The GaN surface was atomically cleaned via a 860°C anneal in an NH3 atmosphere. For the clean GaN surface, upward band bending of ~0.3 ±0.1 eV was measured, and the electron affinity was measured to be ~2.9 eV. Layers of Si were deposited on the GaN surface via Molecular Beam Epitaxy (MBE), and the Si was oxidized by a remote O2 plasma. The oxidation of the Si occurred without oxidizing the GaN. Densification of the created SiO2 film was achieved by annealing the substrate at 650°C. Surface analysis techniques were performed after each process, and yielded a valence band offset of ~2.0 eV, and a conduction band offset of ~3.6 eV for the GaN-SiO2 interface.

We have shown that Zr-based metallization can effectively remove hydrogen from the p-type GaN subsurface, which eventually leads to the formation of an ohmic contact. As the release of hydrogen starts at ∼900°C, the thermal stability of the contact system is of particular importance. The remarkable thermal behavior of the ZrN/ZrB2 metallization is associated to the microstructure of each individual Zr-based compound, as well as to the interfacial crystalline accommodation.

Acceptor (Mg)-doped AlGaN/GaN heterostructures were grown via MOVPE and compared to similarly doped GaN standard films grown in the same reactor. Chemical analysis of the films, via secondary ion mass spectrometry (SIMS), revealed comparable Mg concentrations of ∼2×1019 atoms/cm3 in all films. The Mg-doped GaN standard sample had a sheet conductance of 7-μS compared to a sheet conductance of 20-μS for an AlGaN/GaN heterostructure. The sheet conductance of the AlGaN/GaN heterostructures was higher due to piezoelectric acceptor doping and modulation doping effects in addition to conventional Mg acceptor doping.

Single crystalline (0001) gallium nitride layers, capped with a thin epitaxial aluminum nitride layer, were implanted with magnesium and subsequently annealed in vacuum to 1150-1300 °C for 10-60 minutes. Photoluminescence (PL) measurements showed the typical donor acceptor pair (DAP) transition at 3.25 eV after annealing at high temperatures, which is related to optically active Mg acceptors in GaN. After annealing at 1300 °C a high degree of optical activation of the implanted Mg atoms was reached in the case of low implantation doses. Electrical measurements, performed after removing the AlN-cap and the deposition of Pd/Au contacts, showed no p-type behavior of the GaN samples due to the compensation of the Mg acceptors with native n-type defects.

Single crystalline (0001) gallium nitride layers were implanted with beryllium and subsequently annealed within the range of 300-1100 °C for 10-60 minutes under a flux of atomic nitrogen obtained using a rf plasma source. The nitrogen flux protected the GaN surface from decomposition in vacuum at high temperatures. SIMS measurements revealed that no long range diffusion of the implanted Be occurred at 900 or 1100 °C. XRD spectra showed defect-related peaks in the as-implanted samples; these peaks disappeared upon annealing at 900 °C and higher for 10 minutes. Photoluminescence (PL) easurements showed one new line at 3.35 eV which provided strong evidence for the presence of optically active Be acceptors.

Acceptor (Mg)-doped AlGaN/GaN heterostructures were grown via MOVPE and compared to similarly doped GaN standard films grown in the same reactor. Chemical analysis of the films, via secondary ion mass spectrometry (SIMS), revealed comparable Mg concentrations of ∼2×1019 atoms/cm3 in all films. The Mg-doped GaN standard sample had a sheet conductance of 7-μS compared to a sheet conductance of 20-μS for an AlGaN/GaN heterostructure. The sheet conductance of the AlGaN/GaN heterostructures was higher due to piezoelectric acceptor doping and modulation doping effects in addition to conventional Mg acceptor doping.

Structural transformations in Ni/Si-based contacts to GaN occurring under heat treatment have been studied using transmission electron microscopy and secondary ion mass spectrometry. Transition from non-ohmic to ohmic behavior correlates with reaction between Ni and Si, and decomposition of the initially formed interfacial Ni:Ga:N layer. Transport of dopant atoms from metallization into GaN testifies in favour of the SPR process of ohmic contact formation

Single crystalline (0001) gallium nitride layers, capped with a thin epitaxial aluminum nitride layer, were implanted with magnesium and subsequently annealed in vacuum to 1150-1300 oC for 10-60 minutes. Photoluminescence (PL) measurements showed the typical donor acceptor pair (DAP) transition at 3.25 eV after annealing at high temperatures, which is related to optically active Mg acceptors in GaN. After annealing at 1300 °C a high degree of optical activation of the implanted Mg atoms was reached in the case of low implantation doses. Electrical measurements, performed after removing the AlN-cap and the deposition of Pd/Au contacts, showed no p-type behavior of the GaN samples due to the compensation of the Mg acceptors with native n-type defects.

GaN films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. SEM and TEM analysis are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.

We have shown that Zr-based metallization can effectively remove hydrogen from the p-type GaN subsurface, which eventually leads to the formation of an ohmic contact. As the release of hydrogen starts at ∼900°C, the thermal stability of the contact system is of particular importance. The remarkable thermal behavior of the ZrN/ZrB2 metallization is associated to the microstructure of each individual Zr-based compound, as well as to the interfacial crystalline accommodation.