Research on proactive and reactive aggression has identified covariates unique to each function of aggression, but hypothesized correlates have often not been tested with consideration of developmental changes in or the overlap between the types of aggression. The present study examines the unique developmental trajectories of proactive and reactive aggression over adolescence and young adulthood and tests these trajectories’ associations with key covariates: callous–unemotional (CU) traits, impulsivity, and internalizing emotions. In a sample of 1,211 justice-involved males (ages 15–22), quadratic growth models (i.e., intercepts, linear slopes, and quadratic slopes) of each type of aggression were regressed onto quadratic growth models of the covariates while controlling for the other type of aggression. After accounting for the level of reactive aggression, the level of proactive aggression was predicted by the level of CU traits. However, change in proactive aggression over time was not related to the change in any covariates. After accounting for proactive aggression, reactive aggression was predicted by impulsivity, both at the initial level and in change over time. Results support that proactive and reactive aggression are unique constructs with separate developmental trajectories and distinct covariates.

Accuracy of atom probe tomography measurements is strongly degraded by the presence of phases that have different evaporation fields. In particular, when there are perpendicular interfaces to the tip axis in the specimen, layers thicknesses are systematically biased and the resolution is degraded near the interfaces. Based on an analytical model of field evaporated emitter end-form, a new algorithm dedicated to the 3D reconstruction of multilayered samples was developed. Simulations of field evaporation of bilayer were performed to evaluate the effectiveness of the new algorithm. Compared to the standard state-of-the-art reconstruction methods, the present approach provides much more accurate analyzed volume, and the resolution is clearly improved near the interface. The ability of the algorithm to handle experimental data was also demonstrated. It is shown that the standard algorithm applied to the same data can commit an error on the layers thicknesses up to a factor 2. This new method is not constrained by the classical hemispherical specimen shape assumption.

More than two decades of III-N materials research has led to the production of visible spectrum commercial light-emitting diodes (LEDs) and laser diodes (LDs). Commercial c-plane LEDs are currently limited by efficiency droop which describes the decline in efficiency with increasing input current density. Laser-based sources, however, provide peak efficiencies at much higher current densities and may circumvent efficiency droop limitations. The potential benefits of non-basal plane (NBP) orientations could accelerate the evolution of solid-state lighting from LED to LD sources. Here, we review the progress in long-wavelength (440–590 nm) NBP quantum well LD research and discuss applications in solid-state lighting, visible light communication and smart lighting.

The transport properties of doped and undoped, high quality, plasma-assisted molecular beam epitaxy grown tin dioxide (SnO2) thin films are reviewed. Intentional doping can vary the SnO2 resistivity over more than seven orders of magnitude from a transparent conducting oxide-like conductivity up to the semi-insulating range. A region of high unintentional n-type conductivity was identified in the substrate interface region and had to be accounted for. Sb was a well-behaved shallow donor up to the regime of conducting oxides. In and Ga were too deep acceptors to achieve p-type conductivity but were suitable to render SnO2 semi-insulating. While the surface accumulation layer strongly influenced contact properties, its conductance was negligible. The methodology used here for studying the transport can also be applied to other semiconducting oxides.

Compound semiconductors belong to the most important materials for optoelectronic applications. Many of them exhibit favorable optical properties, such as a direct energy band gap (in contrast to silicon) and high-absorption coefficients over a wide spectral range. Moreover, varying the composition of the compound or substituting some of its elements often allows for controlled band gap engineering and optimization for specific applications. Because many compound semiconductors enable efficient conversion of light into electricity and vice versa, they are commonly used materials for optoelectronic devices.

We studied the effect of extended defects on electrical characteristics of Si doped n-type nonpolar a-plane GaN films. The n-type GaN layers were grown on co-loaded reduced defect density sidewall lateral epitaxial overgrowth (SLEO) a-plane GaN templates and high defect density planar a-plane GaN templates by metalorganic chemical vapor deposition (MOCVD). The highest conductivity value was observed at the carrier concentration of 1.05 × 1019 cm−3 as 261.12 cm2/Vs for SLEO a-GaN and 106.77 cm2/Vs for the planar a-plane GaN samples. At the same doping level, the carrier compensation for SLEO samples was ∼12% less than planar samples.

The performance of conventional c-plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-plane GaN.

The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘semipolar’ planes. A semipolar plane is any plane that may not be classified as a c-, a- or m- plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and planes, for example). It is expected that devices grown on these semipolar planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on semipolar planes is comparable to that for growth on the c-plane.

We demonstrate the first green InGaN/GaN LED grown on a planar semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the semipolar green LEDs.

Ammonothermal growth of GaN was studied to determine its eventual utility for mass production of GaN bulk crystals. Dissolution of GaN in supercritical ammonia with 1 M NaNH2 was investigated through a weight loss method. The time dependence of the weight loss was examined at 500°C and 525°C. Since the weight loss did not reach saturation as a function of time, the solubility limit was not realized. However, experiments demonstrate that GaN has a negative temperature dependence of solubility in supercritical ammonobasic solutions. Based on this result, GaN was grown via fluid transport from metallic Ga to a free-standing GaN single crystal seed by placing the seed crystal in a higher temperature zone and the nutrient in a lower temperature zone. GaN films with thickness of 5 μm (Ga face) and 4 μm (N face) were simultaneously grown on the seed in three days. The surface morphology, optical property, and defect density were found to be different for films on Ga face and N face.

Scanning Kelvin probe microscopy (SKPM) and conductive atomic force microscopy (C-AFM) are used to image surfaces of GaN grown by molecular beam epitaxy (MBE). Numerical simulations are used to assist in the interpretation of SKPM images. Detailed analysis of the same area using both techniques allows imaging of surface potential variations arising from the presence of negatively charged dislocations and dislocation-related current leakage paths. Correlations between the charge state of dislocations, conductivity of leakage current paths, and possibly dislocation type can thereby be established. Approximately 25% of the leakage paths appear to be spatially correlated with negatively charged dislocation features. This is approximately the level of correlation expected due to spatial overlap of randomly distributed, distinct features of the size observed, suggesting that the negatively charged dislocations are distinct from those responsible for localized leakage paths found in GaN. The effects of charged dislocation networks on the local potential profile is modeled and discussed.

We have studied the structural and optical properties of a series of (In,Ga)/GaN multiple quantum wells with identical thicknesses but varied In content grown by plasma-assisted molecular beam epitaxy. Careful choice of the growth parameters returns samples with smooth and abrupt interfaces. The shift of the photoluminescence transition energy with externally applied biaxial tension was investigated. We observed a red-shift for small In contents while a blue-shift was detected for higher In contents. This result is in qualitative agreement with band profile calculations taking into account both the band gap deformation potentials and the piezoelectric polarization in these structures. However, the magnitude of the shift is well in excess of the calculated one. We attribute this finding to a substantial deviation of the piezoelectric constants from those calculated for unstrained material. Finally, we estimate the piezoelectric polarization of InGaN/GaN for linear and non-linear terms in strain.

InGaN multi-quantum-well laser diodes have been fabricated on fully-coalesced laterally epitaxially overgrown (LEO) GaN on sapphire. The laterally overgrown ‘wing’ regions as well as the coalescence fronts contained few or no threading dislocations. Laser diodes fabricated on the low-dislocation-density wing regions showed a reduction in threshold current density from 8 kA/cm2 to 3.7 kA/cm2 compared the those on the high-dislocation ‘window’ regions. Laser diodes also showed a two-fold reduction in threshold current density when comparing those on the wing regions to those fabricated on conventional planar GaN on sapphire. The internal quantum efficiency also improved from 3% for laser diodes on conventional GaN on sapphire to 22% for laser diodes on LEO GaN on sapphire.

Vapor-phase processes such as chemical vapor deposition (CVD) and reactive ion etching are the primary methods for the production-scale synthesis and processing of many high-quality thin-film materials. For example, these processes are widely used in the microelectronics industry for synthesis and lithography of the various semiconducting, insulating, and conducting layers in devices. Understanding the means of controlling the microstructure and composition of these materials is of great technological interest. However a difficulty often encountered in developing vapor-phase processes is an undesirable dependence on trial-and-error methods for optimizing the many process parameters. These parameters include gas composition, flow rate, pressure, and substrate temperature, all of which are typically changing with time. This reliance on empirical methods can be attributed to the tremendous chemical and physical complexity of vapor-phase processes and the lack of appropriate in situ measurement techniques for the vapor-phase environment.

We have initiated a program to apply synchrotron x-ray analysis techniques as real-time probes of film and surface structure during vapor-phase processing. X-rays have a combination of properties which makes them particularly well-suited for these studies. Unlike electrons, x-rays have a sufficiently low absorption to penetrate vapor-phase processing environments and chamber walls. Unlike visible light, x-rays have wavelengths and energies suitable for study of atomic-scale structure and chemistry. A growing number of in situ synchrotron x-ray investigations of film growth and processing demonstrate the power of these techniques.

Periodically loaded line phase shifter circuits using voltage tunable BaSrTiO3 (BST) parallel plate capacitors have been demonstrated at X-band. The first such phase shifter circuit was capable of 100° of phase shift with an insertion loss of 7.6 dB at 10 GHz. Subsequently, the monolithic fabrication procedure was refined resulting in an improved phase shifter circuit with 200° of phase shift and an insertion loss of 6.2 dB at 10 GHz. In addition to promising loss performance (32°/dB) at 10 GHz, the circuits reported here have several desirable features such as moderate control voltages (20 V), room temperature operation, and compatibility with monolithic fabrication techniques.

InGaN multi-quantum-well laser diodes have been fabricated on fully-coalesced laterally epitaxially overgrown (LEO) GaN on sapphire. The laterally overgrown ‘wing’ regions as well as the coalescence fronts contained few or no threading dislocations. Laser diodes fabricated on the low-dislocation-density wing regions showed a reduction in threshold current density from 8 kA/cm2 to 3.7 kA/cm2 compared the those on the high-dislocation ‘window’ regions. Laser diodes also showed a twofold reduction in threshold current density when comparing those on the wing regions to those fabricated on conventional planar GaN on sapphire. The internal quantum efficiency also improved from 3% for laser diodes on conventional GaN on sapphire to 22% for laser diodes on LEO GaN on sapphire.

We have used atomic force microscopy (AFM) to study the effect of common substrate surface treatments for the metal-organic chemical vapor deposition (MOCVD) of GaN on sapphire. It appears that contaminants play a major role in the surface chemistry and strongly influence the morphology of the treated surfaces. In order to investigate the role of these contaminants, we have introduced the concept of “controlled contamination” (CC), namely, exposure of the sapphire surfaces to controlled amounts of potential contaminants in-situ and investigation of the resulting sapphire morphology. The results showed that sapphire, considered to be a very stable oxide surface, is clearly reactive in the GaN MOCVD chemical environment at the high temperatures (HT) employed, allowing us to use CC for obtaining sapphire substrates with controlled roughness. Nevertheless, epitaxial growth using the two-step GaN MOCVD process appears to be very robust and practically insensitive to the (submicronscale) substrate morphology.