Direct nucleation, morphology and compositional tuning of InAs1-x Sb x nanowires on InAs (111) B substrates.

III-V ternary nanowires are interesting due to the possibility of modulating their physical and material properties by tuning their material composition. Amongst them InAs1-x Sb x nanowires are good candidates for applications such as Infrared detectors. However, this material has not been grown directly from substrates, in a large range of material compositions. Since the properties of ternaries are alterable by tuning their composition, it is beneficial to gain access to a wide range of composition tunability. Here we demonstrate direct nucleation and growth of InAs1-x Sb x nanowires from Au seed particles over a broad range of compositions (x = 0.08-0.75) for different diameters and surface densities by means of metalorganic vapor phase epitaxy. We investigate how the nucleation, morphology, solid phase Sb content, and growth rate of these nanowires depend on the particle dimensions, and on growth conditions such as the vapor phase composition, V/III ratio, and temperature. We show that the solid phase Sb content of the nanowires remains invariant towards changes of the In precursor flow. We also discuss that at relatively high In flows the growth mechanism alters from Au-seeded to what is referred to as semi In-seeded growth. This change enables growth of nanowires with a high solid phase Sb content of 0.75 that are not feasible via Au-seeded growth. Independent of the growth conditions and morphology, we report that the nanowire Sb content changes over their length, from lower Sb contents at the base, increasing to higher amounts towards the tip. We correlate the axial Sb content variations to the axial growth rate measured in situ. We also report spontaneous core-shell formation for Au-seeded nanowires, where the core is Sb-rich in comparison to the Sb-poor shell.

Schottky barrier and contact resistance of InSb nanowire field-effect transistors.

Understanding of the electrical contact properties of semiconductor nanowire (NW) field-effect transistors (FETs) plays a crucial role in the use of semiconducting NWs as building blocks for future nanoelectronic devices and in the study of fundamental physics problems. Here, we report on a study of the contact properties of Ti/Au, a widely used contact metal combination, when contacting individual InSb NWs via both two-probe and four-probe transport measurements. We show that a Schottky barrier of height [Formula: see text] is present at the metal-InSb NW interfaces and its effective height is gate-tunable. The contact resistance ([Formula: see text]) in the InSb NWFETs is also analyzed by magnetotransport measurements at low temperatures. It is found that [Formula: see text] in the on-state exhibits a pronounced magnetic field-dependent feature, namely it is increased strongly with increasing magnetic field after an onset field [Formula: see text]. A qualitative picture that takes into account magnetic depopulation of subbands in the NWs is provided to explain the observation. Our results provide solid experimental evidence for the presence of a Schottky barrier at Ti/Au-InSb NW interfaces and can be used as a basis for design and fabrication of novel InSb NW-based nanoelectronic devices and quantum devices.

Demonstration of Sn-seeded GaSb homo- and GaAs-GaSb heterostructural nanowires.

The particle-assisted epitaxial growth of antimonide-based nanowires has mainly been realized using gold as the seed material. However, the Au-seeded epitaxial growth of antimonide-based nanowires such as GaSb nanowires presents several challenges such as for example direct nucleation issues and crystal structure tuning. Therefore, it is of great importance to understand the role of seed material choice and properties in the growth behavior of antimonide-based nanowires to obtain a deeper understanding and a better control on their formation processes. In this report, we have investigated the epitaxial growth of GaSb and GaAs-GaSb nanowires using in situ-formed tin seeds by means of metalorganic vapor phase epitaxy technique. This comprehensive report covers the growth of in situ-formed tin seeds and Sn-seeded GaSb nanowires on both GaAs and GaSb (111)B substrates, as well as GaAs-GaSb nanowires on GaAs (111)B substrates. The growth behavior and structural properties of the obtained GaSb nanowires are further investigated and compared with the Au-seeded counterparts. The results provided by this study demonstrate that Sn is a promising seed material for the growth of GaSb nanowires.

Morphology and composition controlled Ga(x)In(1-x)Sb nanowires: understanding ternary antimonide growth.

Antimonide-based nanowires represent an important new class of material with great promise for both fundamental physics studies and various device applications. We report a comprehensive study on understanding the growth behaviour of GaxIn1-xSb nanowires on GaAs substrates using Au nanoparticles. First, the effect of growth parameters on the morphology and composition of GaxIn1-xSb nanowires is extensively studied over the entire compositional range (from 3 to ~100% of In). Second, the obtained compositional results are explained by a kinetic model, suggesting an Arrhenius-type behavior for the trimethylindium (TMIn) precursor. Third, the particle composition is fully investigated and the implications for growth are discussed with reference to our calculated Au-Ga-In phase diagram. Fourth, a mechanism is presented to explain the temperature-dependent morphology and radial growth of the GaxIn1-xSb nanowires. Finally, we demonstrate homogeneous compositions in both axial and radial directions and the nanowires remain entirely twin-free zinc blende. The understanding gained from this study together with the potential to precisely tailor the band gap, wavelength and carrier mobilities allows fabrication of various GaxIn1-xSb-based nanowire devices.

Self-catalyzed MBE grown GaAs/GaAs(x)Sb(1-x) core-shell nanowires in ZB and WZ crystal structures.

We have investigated the growth of self-catalyzed GaAs/GaAs(x)Sb(1-x) core-shell nanowires directly on Si(111) substrates by molecular beam epitaxy. The compositions of the GaAs(x)Sb(1-x) shells are tuned in a wide range where the Sb-content is varied from 10 to ~70%, covering the miscibility gap. In addition, the GaAs(x)Sb(1-x) shells are grown on both zinc blende (ZB) and wurtzite (WZ) crystal structures. Morphological and structural characterizations of the grown nanowires indicate successful transfer of the GaAs core crystal structure to the GaAs(x)Sb(1-x) shells for both ZB and WZ nanowires, with slower shell growth rate on the WZ segments.

Uniform and position-controlled InAs nanowires on 2" Si substrates for transistor applications.

This study presents a novel approach for indirect integration of InAs nanowires on 2'' Si substrates. We have investigated and developed epitaxial growth of InAs nanowires on 2'' Si substrates via the introduction of a thin yet high-quality InAs epitaxial layer grown by metalorganic vapor phase epitaxy. We demonstrate well-aligned nanowire growth including precise position and diameter control across the full wafer using very thin epitaxial layers (<300 nm). Statistical analysis results performed on the grown nanowires across the 2'' wafer size verifies our full control on the grown nanowire with 100% growth yield. From the crystallographic viewpoint, these InAs nanowires are predominantly of wurtzite structure. Furthermore, we show one possible device application of the aforementioned structure in vertical wrap-gated field-effect transistor geometry. The vertically aligned InAs nanowires are utilized as transistor channels and the InAs epitaxial layer is employed as the source contact. A high uniformity of the device characteristics for numerous transistors is further presented and RF characterization of these devices demonstrates an f(t) of 9.8 GHz.