Selective area molecular beam epitaxy of InSb on InP(111): from thin films to quantum nanostructures.

InSb is a material of choice for infrared as well as spintronic devices but its integration on large lattice mismatched semi-insulating III-V substrates has so far altered its exceptional properties. Here, we investigate the direct growth of InSb on InP(111)substrates with molecular beam epitaxy. Despite the lack of a thick metamorphic buffer layer for accommodation, we show that quasi-continuous thin films can be grown using a very high Sb/In flux ratio.

InGaAs quantum dot chains grown by twofold selective area molecular beam epitaxy.

Increasing quantum confinement in semiconductor quantum dot (QD) systems is essential to perform robust simulations of many-body physics. By combining molecular beam epitaxy and lithographic techniques, we developed an approach consisting of a twofold selective area growth to build QD chains. Starting from 15 nm-thick and 65 nm-wide in-plane InGaAs nanowires on InP substrates, linear arrays of InGaAs QDs were grown on top, with tunable lengths and separations.

Ultrahigh vacuum Raman spectroscopy for the preparation of III-V semiconductor surfaces.

Raman spectroscopy is well-suited for the characterization of semiconductor materials. However, due the weakness of the Raman signal, the studies of thin semiconductor layers in complex environments, such as ultrahigh vacuum, are rather scarce. Here, we have designed a Raman apparatus based on the use of a fiber optic probe, with a lens collecting the backscattered light directly inserted in ultrahigh vacuum.

Improving the intrinsic conductance of selective area grown in-plane InAs nanowires with a GaSb shell.

The nanoscale intrinsic electrical properties of in-plane InAs nanowires grown by selective area epitaxy are investigated using a process-free method involving a multi-probe scanning tunneling microscope. The resistance of oxide-free InAs nanowires grown on an InP(111)substrate and the resistance of InAs/GaSb core-shell nanowires grown on an InP(001) substrate are measured using a collinear four-point probe arrangement in ultrahigh vacuum. They are compared with the resistance of two-dimensional electron gas reference samples measured using the same method and with the Van der Pauw geometry for validation.

Mid-wave infrared sensitized InGaAs using intraband transition in doped colloidal II-VI nanocrystals.

Narrow bandgap nanocrystals (NCs) are now used as infrared light absorbers, making them competitors to epitaxially grown semiconductors. However, these two types of materials could benefit from one another. While bulk materials are more effective in transporting carriers and give a high degree of doping tunability, NCs offer a larger spectral tunability without lattice-matching constraints.

In-plane InGaAs/Ga(As)Sb nanowire based tunnel junctions grown by selective area molecular beam epitaxy.

In-plane InGaAs/Ga(As)Sb heterojunction tunnel diodes are fabricated by selective area molecular beam epitaxy with two different architectures: either radial InGaAs core/Ga(As)Sb shell nanowires or axial InGaAs/GaSb heterojunctions. In the former case, we unveil the impact of strain relaxation and alloy composition fluctuations at the nanoscale on the tunneling properties of the diodes, whereas in the latter case we demonstrate that template assisted molecular beam epitaxy can be used to achieve a very precise control of tunnel diodes dimensions at the nanoscale with a scalable process. In both cases, negative differential resistances with large peak current densities are achieved.

Engineering a Robust Flat Band in III-V Semiconductor Heterostructures.

Electron states in semiconductor materials can be modified by quantum confinement. Adding to semiconductor heterostructures the concept of lateral geometry offers the possibility to further tailor the electronic band structure with the creation of unique flat bands. Using block copolymer lithography, we describe the design, fabrication, and characterization of multiorbital bands in a honeycomb InGaAs/InP heterostructure quantum well with a lattice constant of 21 nm.

Morphology and valence band offset of GaSb quantum dots grown on GaP(001) and their evolution upon capping.

This work presents a detailed study of GaSb quantum dot (QD) epitaxy on (001) GaP substrates by means of molecular beam epitaxy. Despite the large mismatch between GaP and GaSb, we show that in the nucleation-diffusion regime, the QD size distribution follows the predictions of the scaling theory. Scanning transmission electron microscopy analysis of grown QDs reveal that they are plastically relaxed by 60° pairs of misfit dislocations and the valence band offset measured by x-ray photoelectron spectroscopy on such QDs amounts to 0.

Nonstoichiometric Low-Temperature Grown GaAs Nanowires.

The structural and electronic properties of nonstoichiometric low-temperature grown GaAs nanowire shells have been investigated with scanning tunneling microscopy and spectroscopy, pump-probe reflectivity, and cathodoluminescence measurements. The growth of nonstoichiometric GaAs shells is achieved through the formation of As antisite defects, and to a lower extent, after annealing, As precipitates. Because of the high density of atomic steps on the nanowire sidewalls, the Fermi level is pinned midgap, causing the ionization of the subsurface antisites and the formation of depleted regions around the As precipitates.

Impact of P/In flux ratio and epilayer thickness on faceting for nanoscale selective area growth of InP by molecular beam epitaxy.

The impact of the P/In flux ratio and the deposited thickness on the faceting of InP nanostructures selectively grown by molecular beam epitaxy (MBE) is reported. Homoepitaxial growth of InP is performed inside 200 nm wide stripe openings oriented either along a [110] or [1-10] azimuth in a 10 nm thick SiO2 film deposited on an InP(001) substrate. When varying the P/In flux ratio, no major shape differences are observed for [1-10]-oriented apertures.