1,721,031 research outputs found
Advanced TEM Analysis of Strain-Balanced Si/SiGe Resonant Tunnelling Diode Structures
No full textWe present a TEM analysis of a series of Si/SiGe resonant tunnelling diode structures which contain Si1-xGex quantum wells (x of 0.4 and 1.0) grown on a range of (001) Si1-yGey virtual substrates (y of 0.15, 0.2 and 0.3). It is found that the dislocation density in the graded region of the virtual substrate increases with the y parameter, as expected. The subsequent effect of this, however, is to increase the amplitude of RMS roughness of the substrate surface, which ranges from 2.0 to 6.7 rim. Quantum wells with x = 0.4 are found to be highly planar; however, at x = 1.0 the wells undulate significantly due to misfit strain
How InGaAs islands form on GaAs substrates: the missing link in the explanation of the Stranski-Krastanow transition
No full textThe structure of epitaxial InGaAs / GaAs layers during early stages of growth, just at the onset of islanding, is investigated ex-situ by atomic force microscopy and transmission electron microscopy. Nano-scale compositional measurements of uncapped islands by electron energy-loss imaging in cross-section allow the quantification of In gradients in the islanded layers. The In composition at the island apices is shown to be more than twice the nominal composition, while In depletion of the surrounding flat regions to a similar degree is observed. These lateral compositional inhomogeneities occur as soon as a sufficiently In enriched surface layer has been built up and are considered the driving force for the Stranski-Krastanow transition
Electron energy loss spectroscopic profiling of semiconductor hetero- and nano-structures: theory, implementation, applications
No full textThe method of energy loss spectroscopic profiling (ELSP) in a transmission
electron microscope is described, with emphasis on the implementation for a post-columnar
energy filter and the optimisation of both energy and spatial resolution. Applications to thin film
semiconductors (SiGe / Si, ZnMgSSe / ZnSe and Cd(Mn,Mg)Te / CdTe), to oxide layers
(SrTiO3 / (La0.7Ca0.3)MnO3) and to nano-particles (LaPO4:Ce) demonstrate the potential of this
technique for solving physical, chemical or technological problems related to diffusion and
segregation of elements otherwise not readily accessible. Possible quantification procedures and
recent results are presented
Structural characterisation of MBE grown zinc-blende Ga1-xMnxN/GaAs(001) as a function of Ga flux
Get PDFGa1-xMnxN films grown on semi-insulating GaAs(001) substrates at 680°C with fixed Mn flux and varied Ga flux demonstrated a transition from zinc-blende/wurtzite mixed phase growth for low Ga flux (N-rich conditions) to zinc-blende single phase growth with surface Ga droplets for high Ga flux (Ga-rich conditions). N-rich conditions were found favourable for Mn incorporation in GaN lattice. α-MnAs inclusions were identified extending into the GaAs buffer layer
Analysis of Terahertz-Emitting SiGe Quantum Cascade Structures by Transmission Electron Microscopy
No full textTest structures have been grown onto SiGe virtual substrates, with the first being to identify the effect on quantum well morphology of increasing Ge concentration have used a combination of energy dispersive X-ray microanalysis, electron energy-loss imaging and scanning transmission electron microscopy to measure the compositions of the various quantum wells. There is increasing interest in developing optical device structures in the far infrared (THz) region of the electromagnetic spectrum, an area that until had been relatively inaccessible for many science and engineering applications. The significant interest stems from possible applications relating to imaging and sensing in medical-related areas. Transmission electron microscopy and scanning transmission electron microscopy have been used to characterize the microstructure of quantum wells grown over a range of different germanium concentrations. Quantum well structures subsequently grown onto a 20% SiGe virtual substrate with a Ge concentration of 30% were found to be highly uniform and free of morphological distortions
Nucleation, crystallisation and phase segregation in HfO2 and HfSiO
No full textHafnia and hafnium silicate thin films and bulk powders were analysed using thermal analysis, X-ray diffraction and transmission electron microscope techniques to improve understanding of the crystallisation mechanism of the dielectric material. It was found that thin films exhibit instability under device processing conditions. Starting precursors greatly affect the crystallisation pathway in the bulk materials. By studying these phenomena a better understanding of the chemistry involved during crystallisation can be gained
Growth and surface characterization of piezoelectric AlN thin films on silicon (100) and (110) substrates
Get PDFThis work investigates the fundamental growth of c-axis oriented piezoelectric AlN thin films by RF reactive sputtering on p-type (100) and (110) silicon substrates. Substrates are treated with a 1% HF solution before deposition to remove the native oxide followed by backsputtering using argon ions. X-ray diffraction shows a (0001) oriented columnar texture of AlN grains which is the preferred orientation for piezoelectric applications. TEM shows the presence of a 4 nm thick semi-crystalline interface between silicon and the AlN layer. A basic growth mechanism is proposed from microstructural observations
Nanoscale characterisation of MBE-grown GaMnN / (001) GaAs
Get PDFThe growth of cubic (Ga,Mn)N/(001)GaAs heterostructures by plasma assisted molecular beam epitaxy has been appraised as a function of Ga:N ratio, Mn concentration and growth temperature. The combined analytical techniques of EFTEM, EDX, CBED and dark field imaging have been used to appraise the Mn distributions within (Ga,Mn)N epilayers. Improved incorporation efficiency of Mn is associated with growth under N-rich conditions, but Mn incorporation may be enhanced under Ga-rich conditions at reduced growth temperatures. The surfactant behaviour of Mn during the growth of this spintronic system determines the resultant alloy composition
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