Влияние давления при эпитаксии на свойства слоев GaN

Growth of GaN layers by MOVPE on sapphire substrates at various pressures, including above atmospheric, was studied. It is shown that epitaxy at higher pressures does not change the crystal perfection of the layers, the electron mobility, and the impurities incorporation, but leads to the formation of a surface with a smaller lateral scale of inhomogeneities. The epitaxy pressure also affects the ratio of the intensity of the band-edge and impurity-related lines in the photoluminescence spectra and the leakage currents in the reverse-biased Schottky barrier.

Исследование однородности состава по толщине слоев GaInAsP, полученных на подложках InP методом газофазной эпитаксии

GaInPAs/InP heterostructures grown by low pressure (0.1 bar, 600 oC) metal-organic chemical vapor phase deposition were investigated. The thicknesses of grown GaInAsP layers were about 1 µm. For the epitaxial layers Ga_1-xIn_xP_1-yAs_y) with average compositions of x = 0.77 – 0.87 and y = 0.07 – 0.42 the variation of V group elements content y with the epilayer depth were revealed, weher the compositions of V-group elements were changed up to Δy = 0.1 atomic fractions in V group elements sublattice. In most cases, y change occurs in a GaInAsP region up to 200 nm thick adjacent to the InP. In some cases, y changes throughout the whole GaInPAs layer thickness. Fo the epitaxial layers with a satisfactory crystal perfection the less was the mismatch between the substrate and the GaInPAs epitaxial layer, the smaller was the value of Δy. For GaInPAs layers characterized by a low degree of crystal perfection and a high lattice mismatch between GaInAsP and InP layers, the value of Δy was about zero. These data let us suggest that the incorporation of atoms of the V group in the epitaxial layer strongly depends on elastic deformation of the growing monolayer, that is mismatched with the underlying crystal surface.

Исследование влияния структурных дефектов на спектры фотолюминесценции в n-3C-SiC

Photoluminescence (PL) spectra have been studied in 3 C -SiC/4 H -SiC heterostructures and 3 C ‑SiC single crystals. It was shown that epitaxial 3 C -SiC layers grown on 4 H -SiC substrates have a markedly poorer crystal perfection than do 3 C -SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3 C -SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3 C -SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

Электронографическое изучение структуры эпитаксиального графена, сформированного путем термического разложения SiC(0001) в атмосфере Ar и в высоком вакууме

The structure of epitaxial graphene formed by thermal destruction of silicon carbide surface in the conditions of vacuum synthesis and in an Ar environment has been studied by reflection electron diffraction. As a result of the conducted study it is found the notably more homogeneous graphene coating of buffer layer on the SiC surface under the graphene formation on the polytypes 4H- и 6H- SiC(0001) surfaces in the inert environment as against the graphene synthesis in vacuum. The dependence of quality of the covering from degree of initial single crystal perfection is shown.

Влияние метода формирования высокоомного буферного слоя GaN на свойства гетероструктур InAlN/GaN и AlGaN/GaN с двумерным электронным газом

AlGaN/AlN/GaN and InAlN/AlN/GaN structures with 2D electron gas have been grown on sapphire substrates by metal-organic vapor-phase epitaxy. The suppression of the parasitic conductivity of buffer GaN layers was provided either by intentionally raising the density of edge dislocations or by doping with iron (GaN:Fe). It was shown that using GaN buffer layers with a better crystal perfection and more planar surface results in the electron mobility in the 2D channel for carriers becoming 1.2–1.5 times higher.

How do specimen preparation and crystal perfection affect structure factor measurements by quantitative convergent-beam electron diffraction?

The effectiveness of tripod polishing and crushing as methods of mechanically preparing transmission electron microscopy specimens of hard brittle inorganic crystalline materials is investigated via the example of cerium hexaboride (CeB6). It is shown that tripod polishing produces very large electron-transparent regions of very high crystal perfection compared to the more rapid technique of crushing, which produces crystallites with a high density of imperfections and significant mosaicity in the case studied here where the main crystallite facets are not along the natural {001} cleavage planes of CeB6. The role of specimen quality in limiting the accuracy of structure factor measurements by quantitative convergent-beam electron diffraction (QCBED) is investigated. It is found that the bonding component of structure factors refined from CBED patterns obtained from crushed and tripod-polished specimens varies very significantly. It is shown that tripod-polished specimens yield CBED patterns of much greater integrity than crushed specimens and that the mismatch error that remains in QCBED pattern matching of data from tripod-polished specimens is essentially nonsystematic in nature. This stands in contrast to QCBED using crushed specimens and lends much greater confidence to the accuracy and precision of bonding measurements by QCBED from tripod-polished specimens.