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The strain relief and dislocation motion in III-nitride films that are grown on step-free 4H-SiC mesas are studied. The results show that the nucleation of threading dislocations in the absence of interfacial steps is an extremely difficult process, which proves that the strain relief for such III-nitride films is not dominated by the greater excess stress driving dislocation tilt.

Ultraviolet photoluminescence, transmission electron microscopy and KOH etching were used to characterize extended defects in 4H-SiC epilayers grown at high growth rates (18 μm/h). Layers exhibited high densities of in-grown stacking faults and dislocation half-loops. The stacking faults were 8H Shockley-type faults. The Burgers vector of the dislocation half-loops was in the (0001) basal plane. Both defects nucleate within the epilayer at early stages of growth. Defect nucleation is directly correlated with high initial growth rate and is not related to any defects/heterogeneities in the substrate or epilayer. Epilayer growth by nucleation of two-dimensional islands is proposed as a possible mechanism for the formation of both defects, through nucleation of faulted Si-C bilayers. [ABSTRACT FROM AUTHOR]

This manuscript presents the first observation of the space-charge-limited current (SCLC) conduction mechanism in individual heterostructure nanowires (NWs). This effect is exploited to extract size-dependent carrier densities and to demonstrate surface-dominated behavior for these technologically relevant nanostructures. Mobile carrier densities were shown to increase from 2.5 × 1016 to 5.6 × 1017 cm-3, as NW width decreased from 200 to 50 nm. This size-dependent behavior is a consequence of the increasing influence of near-surface confined carriers as widths decrease. Traps impact the SCLC response and were characterized as an exponential band edge tail with an average characteristic energy of 75 meV. In addition to the specific materials properties extracted, these results further demonstrate the tendency for low-dimensional materials (1D NWs) to exhibit SCLC at much lower injection fluxes compared to their higher dimensional (2D heterostructure field-effect transistors) counterparts. [ABSTRACT FROM AUTHOR]

Atomic layer deposition was employed to deposit relatively thick (∼30 nm) aluminum oxide (Al2O3) using trimethylaluminum and triply-distilled H2O precursors onto epitaxial graphene grown on the Si-face of silicon carbide. Ex situ surface conditioning by a simple wet chemistry treatment was used to render the otherwise chemically inert graphene surface more amenable to dielectric deposition. The obtained films show excellent morphology and uniformity over large (∼64 mm2) areas (i.e., the entire sample area), as determined by atomic force microscopy and scanning electron microscopy. X-ray photoelectron spectroscopy revealed a nearly stoichiometric film with reduced impurity content. Moreover, from capacitance-voltage measurements a dielectric constant of ∼7.6 was extracted and a positive Dirac voltage shift of ∼1.0 V was observed. The graphene mobility, as determined by van der Pauw Hall measurements, was not affected by the sequence of surface pretreatment and dielectric deposition. [ABSTRACT FROM AUTHOR]

The dominant recombination processes controlling the carrier lifetime in n-type 4H–SiC epitaxial layers grown with low concentrations of the Z1/2 defect (the dominant bulk lifetime killer), where Z1/2 no longer determines the lifetime, have been investigated by studying the variation in the carrier lifetime with temperature. The temperature dependent lifetimes were obtained primarily by low-injection photoluminescence decay for several low-Z1/2 epilayers over a wide temperature range. The results were fitted to simulations of the temperature dependent recombination rate, where bulk, surface and interface recombination was considered. No significant contribution from other bulk defects was observed, and upper limits to the bulk recombination rate were found to be consistent with the low Z1/2 concentrations measured in these materials. There was also no significant contribution from carrier capture at the epilayer/substrate interface, which is consistent with behavior expected at low injection for low-doped epilayers grown on n+ substrates. Corresponding high-injection measurements exhibited very different behavior, consistent with the surface/interface under flat-band conditions. Consequently, it is concluded that for low-Z1/2 materials, control of the carrier lifetime has not been transferred from Z1/2 to another bulk defect, but is instead dominated by surface and interface recombination. Simulations suggest that further enhancement of the total lifetime under the high injection conditions of a device structure would require very thick epilayers, effectively passivated surface and interface recombination and a further reduction in the remaining Z1/2 concentrations. The temperature dependence of the low-injection carrier lifetime was also found to provide a method to estimate the surface band bending and the surface defect density. [ABSTRACT FROM AUTHOR]

The impact of surface depletion on the electronic properties of semiconductor nanowires (NWs) is explored both theoretically and experimentally. The impact of dopant concentration, surface barrier height, and NW radius on surface depletion and extracted material properties are determined by solving Poisson’s equation for the cylindrical system. The theoretical results reveal a size-dependent systematic error in carrier concentration extraction, which is verified through experiment. Interrogation of GaN NWs with radii from 15 to 70 nm exposed an error that reaches over an order of magnitude for the samples studied. These data compared favorably to an analytical treatment assuming physically reasonable material properties. While this manuscript focuses on GaN, the systematic error discussed will be present for any semiconducting NW, which exhibits surface band bending and therefore influences the behavior and characterization of a wide range of semiconducting nanoelements. [ABSTRACT FROM AUTHOR]

Bulk growth of 4H-SiC is challenging due to the required high growth temperatures and gradients used in sublimation physical vapor transport that are difficult to control, particularly over large diameter boules. We used x-ray diffraction mapping to show concave crystal plane curvature in substrates from five commercial suppliers with two suppliers producing wafers with <=2° curvature. The extent of curvature varied little for substrates from any particular supplier. Maps of peak position and full width at half maximum from symmetric and asymmetric reflections were used to identify defective regions in the crystal. Closer examination of the rocking curves in the defective regions found a low density of low angle grain boundaries only in substrates from one supplier. [ABSTRACT FROM AUTHOR]

Presents a study that characterized electron cyclotron resonance plasmas by vacuum ultraviolet spectroscopy. Method of the study; Results and discussion; Conclusion.

Provides information on a study that reported the growth of gallium nitride films using the electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy method. Methodologies used; Results and discussion; Conclusions.

Recent breakthroughs in bulk crystal growth of β-Ga2O3 by the edge-defined film-fed technique has led to the commercialization of large-area β-Ga2O3 substrates. Standard epitaxy approaches are being utilized to develop various thin-film β-Ga2O3 based devices including lateral transistors. This article will discuss the challenges for metal organic chemical vapor deposition (MOCVD) of β-Ga2O3 and the design criteria for use of this material system in power electronic device structures. [ABSTRACT FROM AUTHOR]

Details a study which investigated the influence of plasma etching on the electrical properties of n-type gallium nitride thin films. Experimental procedures; Influence of the presence of hydrogen in the etching plasma on free-electron density; Description of the annealing behavior of the thin films.