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The effect of growth temperature and subsequent annealing on the epitaxy of both single- and few-layer TaSe 2 on Se-terminated GaP(111) B substrates is investigated. The selective growth of the 1T and 1H phases is shown up to 1 ML according to X-ray and ultraviolet photoelectron spectroscopies. The 1H monolayer, favored at low temperatures, exhibits a very homogeneous coverage after annealing, while the 1T ML, grown at high temperatures, is characterized by a better in-plane orientation. Moreover, X-ray photoelectron diffraction spectroscopy performed on 1T submonolayers shows a negligible amount of mirror twins. By contrast, in multilayers, scanning transmission electron microscopy always reveals a mixture of 2H a and 3R polytypes with very few 1T. In addition, the multilayers become Se-deficient above 500 °C, and a new interfacial phase identified as Ta 1+ x Se 2 or TaP appears. Finally, the optimized multilayers grown between 250 and 500 °C exhibit a similar metallic behavior with a resistivity comparable to the bulk one with valuable outcomes in the formation of electrical contacts for two-dimensional (2D) material-based devices.

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) B 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. The quality of the films is further studied with Hall measurements on large-scale devices to assess the impact of the InSb surface and InSb/InP interface on the electronic properties. Taking advantage of the optimized growth conditions for the formation of thin films, the selective area molecular beam epitaxial growth of nanostructures is subsequently investigated. Based on cross-sectional transmission electron microscopy and scanning near-field optical microscopy in the middle-wave infrared, ultra-thin and very long in-plane InSb nanowires as well as more complex nanostructures such as nano-rings and crosses are achieved with a good structural quality., (© 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

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 In 0.53 Ga 0.47 As nanowires on InP substrates, linear arrays of In 0.53 Ga 0.47 As QDs were grown on top, with tunable lengths and separations. Kelvin probe force microscopy performed at room temperature revealed a change of quantum confinement in chains with decreasing QD sizes, which was further emphasized by the spectral shift of quantum levels resolved in the conduction band with low temperature scanning tunneling spectroscopy. This approach, which allows the controlled formation of 25 nm-thick QDs with a minimum length and separation of 30 nm and 22 nm respectively, is suitable for the construction of scalable fermionic quantum lattices., (© 2024 IOP Publishing Ltd.)

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. The solution has been tested for the preparation of III-V semiconductor surfaces, which requires the recovery of their atomic reconstruction. The surfaces were either protected with a thin As amorphous layer or covered with a native oxide prior to their treatment. The analysis of the Raman spectra, which was correlated with the study of the surfaces with low temperature scanning tunneling microscopy at the end of the cleaning process, shows the high potential of Raman spectroscopy for monitoring the cleanliness of III-V semiconductor heterostructures in situ., (© 2023 Author(s). Published under an exclusive license by AIP Publishing.)

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) B 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. A significant improvement of the conductance is achieved when the InAs nanowires are fully embedded in GaSb, exhibiting an intrinsic sheet conductance close to the one of the quantum well counterpart., (© 2023 IOP Publishing Ltd.)

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. Here, we investigate the potential of sensitizing InGaAs in the mid-wave infrared throughout the intraband transition of self-doped HgSe NCs. Our device geometry enables the design of a photodiode remaining mostly unreported for intraband-absorbing NCs. Finally, this strategy allows for more effective cooling and preserves the detectivity above 10 8 Jones up to 200 K, making it closer to cryo-free operation for mid-infrared NC-based sensors.

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., (© 2022 IOP Publishing Ltd.)

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 In 0.53 Ga 0.47 As/InP heterostructure quantum well with a lattice constant of 21 nm. Thanks to an optimized surface quality, scanning tunnelling spectroscopy reveals the existence of a strong resonance localized between the lattice sites, signature of a p-orbital flat band. Together with theoretical computations, the impact of the nanopatterning imperfections on the band structure is examined. We show that the flat band is protected against the lateral and vertical disorder, making this industry-standard system particularly attractive for the study of exotic phases of matter.

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 0.5 eV. After capping, the QD morphology is strongly modified with a large P/Sb exchange-segregation reaction, which even leads to the formation of core-shell nanostructures. Remarkably the resulting QD layer is coherent to the substrate without any remaining misfit dislocation and exhibits still strong composition modulations.

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. Controlling their incorporation offers a way to obtain unique electronic and optical properties that depart from the ones found in conventional GaAs nanowires.

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. On the other hand, the InP nanostructure cross sections strongly evolve for [110]-oriented apertures for which (111)B facets are more prominent and (001) ones shrink for large P/In flux ratio values. These results show that the growth conditions allow tailoring the nanocrystal shape. They are discussed in the framework of the equilibrium crystal shape model using existing theoretical calculations of the surface energies of different low-index InP surfaces as a function of the phosphorus chemical potential, directly related to the P/In ratio. Experimental observations strongly suggest that the relative (111)A surface energy is probably smaller than the calculated value. We also discuss the evolution of the nanostructure shape with the InP-deposited thickness.