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Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowire constituents have been monitored prior to and after cleaning from native oxides. The cleaning process mainly affected the Asoxides and was accompanied by an energy shift of the core-level spectra towards lower binding energy, suggesting that the As-oxides turn the nanowire surfaces to n-type. After cleaning, both As and Ga core-levels revealed an energy shift of about -0.3 eV for core/shell compared to core reference nanowires. With respect to depth dependence and in agreement with calculated strain distribution and electron quantum confinement, the observed energy shift is interpreted by band bending of core-levels at the heterointerface between the GaAs nanowire core and the InAs shell. [ABSTRACT FROM AUTHOR]

Using plan-view and cross-sectional scanning tunneling microscopy, the shape and composition of InAs/GaAs quantum dots are investigated before and after capping by GaAs. During capping, the original pyramidally shaped quantum dots become truncated, resulting in a flat (001) top facet and steeper side facets. The InAs quantum dots are found to be intermixed at their top with GaAs due to material rearrangement. Since the bottom interface of quantum dots and wetting layer is always sharp, this intermixing occurs during capping and not during quantum dot growth. Considering strain energies, a model for the capping is presented. [ABSTRACT FROM AUTHOR]

Abstract: We present a synchrotron-based XPS investigation on the interface between InAs and Al2O3 or HfO2 layers, deposited by ALD at different temperatures, for InAs substrates with different surface orientations as well as for InAs nanowires. We reveal the composition of the native Oxide and how the high-κ layer deposition reduces Oxide components. We demonstrate some of the advantages in using synchrotron radiation revealing the variation in Oxide composition as a function of depth into the subsurface region and how we can indentify Oxides even on nanowires covering only a small fraction of the surface. [Copyright &y& Elsevier]

Thin high-κ oxide films on InAs, formed by atomic layer deposition, are the key to achieve high-speed metal-oxide-semiconductor devices. We have studied the native oxide and the interface between InAs and 2 nm thick Al2O3 or HfO2 layers using synchrotron x-ray photoemission spectroscopy. Both films lead to a strong oxide reduction, obtaining less than 10% of the native As-oxides and between 10% and 50% of the native In-oxides, depending on the deposition temperature. The ratio of native In- to As-oxides is determined to be 2:1. The exact composition and the influence of different oxidation states and suboxides is discussed in detail. [ABSTRACT FROM AUTHOR]

Thin high-κ oxide films on InAs, formed by atomic layer deposition, are the key to achieve high-speed metal-oxide-semiconductor devices. We have studied the native oxide and the interface between InAs and 2 nm thick Al2O3 or HfO2 layers using synchrotron x-ray photoemission spectroscopy. Both films lead to a strong oxide reduction, obtaining less than 10% of the native As-oxides and between 10% and 50% of the native In-oxides, depending on the deposition temperature. The ratio of native In- to As-oxides is determined to be 2:1. The exact composition and the influence of different oxidation states and suboxides is discussed in detail. [ABSTRACT FROM AUTHOR]

Cross-sectional scanning tunneling microscopy is used to study the spatial structure and composition of self-assembled InAs nanostructures grown on InGaAsP lattice matched to the InP substrate. Images of the (110) and [formula] cleavage surfaces reveal InAs quantum dashes of different lateral extensions. They are found to be about 60 nm long, about 15 nm wide, about 2 nm high, and to consist of pure InAs. Furthermore, the quaternary InGaAsP matrix material below, in between, and above the quantum-dash layers shows a strong lateral contrast variation, which is related to a partial decomposition into columns of more InAs-rich and more GaP-rich regions. The effect is particularly pronounced along the [110] direction. A quantitative analysis of this strain-induced contrast yields a decomposition characterized by variations of the group-III and/or group-V concentrations in the order of ±10%. The data strongly indicate that the strain at the growth surface induced by the decomposition of the underlying matrix material plays an important role for the nucleation and formation of the quantum dashes as well as for their unexpected stacking over interlayer distances as large as 40 nm. Despite of the observation that the quantum dashes enforce the decomposition, which was already developed directly at the InGaAsP/InP interface without any influence of the subsequently grown InAs quantum dashes. [ABSTRACT FROM AUTHOR]