The structure of InAlGaN layers grown by metal organic vapour phase epitaxy: effects of threading dislocations and inversion domains from the GaN template.

Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer surface, and this is related to the change in growth kinetics on top and at the immediate surroundings of the ID.

The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells.

In this work, we analyse the microstructure and local chemical composition of green-emitting Inx Ga1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.

Effective absorption correction for energy dispersive X-ray mapping in a scanning transmission electron microscope: analysing the local indium distribution in rough samples of InGaN alloy layers.

We have applied our previous method of self-consistent k*-factors for absorption correction in energy-dispersive X-ray spectroscopy to quantify the indium content in X-ray maps of thick compound InGaN layers. The method allows us to quantify the indium concentration without measuring the sample thickness, density or beam current, and works even if there is a drastic local thickness change due to sample roughness or preferential thinning. The method is shown to select, point-by-point in a two-dimensional spectrum image or map, the k*-factor from the local Ga K/L intensity ratio that is most appropriate for the corresponding sample geometry, demonstrating it is not the sample thickness measured along the electron beam direction but the optical path length the X-rays have to travel through the sample that is relevant for the absorption correction.

Influence of nanoscale faceting on the tunneling properties of near broken gap InAs/AlGaSb heterojunctions grown by selective area epitaxy.

We report on the selective area molecular beam epitaxy of InAs/AlGaSb heterostructures on a GaSb (001) substrate. This method is used to realize Esaki tunnel diodes with a tunneling area down to 50 nm × 50 nm. The impact of the size reduction on the peak current density of the diode is investigated, and we show how the formation of the InAs facets can deeply affect the band-to-band tunneling properties of the heterostructure. This phenomenon is explained by the surface-dependent incorporation of Si dopant during growth.

Defect structure in heteroepitaxial semipolar (1122) (Ga, Al)N.

The defect structures in semipolar (1122)-GaN, AlN layers grown on m-sapphire by metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are characterized by transmission electron microscopy. The epitaxial relationships are identified as [1010](GaN) || [1120]sap and [1213](GaN) || [0001]sap. Defects are identified as mostly partial dislocations, I1-basal and prismatic stacking faults. The density of dislocations is of the order of 5.5 × 10(9) cm(-2). They are Frank-Shockley partial dislocations with b = 1/6<2023> (90%), Shockley partial dislocations with b = 1/3<1010> (8%) and perfect dislocations of a-type with b = 1/3<1120> (2%). This is in contrast with the growth in c- or a-orientations, where the large majority of extended defects consists of perfect dislocations. Upon MBE regrowth of GaN on MOVPE GaN, no additional defects are generated, although the defects in the substrate propagate through the overgrown layer. However, in the case of MBE deposition of AlN on MOVPE GaN, new threading dislocations of the type b = 1/3<1123> are generated taking stepped and curved structures along their lines.

High Curie temperature for La(0.7)Sr(0.3)MnO(3) thin films deposited on CeO(2) /YSZ-based buffered silicon substrates.

Two kinds of epitaxial structures were grown by standard pulsed laser deposition on (001) Si, namely La(0.7)Sr(0.3)MnO(3)/Bi(4)Ti(3)O(12)/CeO(2) /YSZ/Si (BTO-based), and La(0.7)Sr(0.3)MnO(3)/SrTiO(3)/CeO(2) /YSZ/Si (STO-based) multilayers. The samples were investigated by means of x-ray diffraction, transmission electron microscopy, magnetic and transport measurements. The Curie temperature T(C) of the BTO-based samples was found to be higher (360 K) than for the typical reference epitaxial LSMO film grown on (001) SrTiO(3) single crystal (345 K), due to high compressive in-plane strain. The STO-based samples show high structural quality, low roughness and high T(C) (350 K), making them interesting candidates for use in innovative LSMO-based bolometers or spintronic devices operating at room temperature.