GaN-based spin light-emitting diodes (spin-LEDs) are attractive for realizing room-temperature spin-controlled light emission in efficient, color-tunable devices. In this work, we demonstrate spin injection in a GaN spin-LED fabricated on a Si substrate using wafer-bonding technology. An inverted n-i-p LED structure with n-type GaN on top facilitates the injection of spin-polarized electrons from a ferromagnetic Au/Co/MgO spin-injector layer grown by molecular beam epitaxy. At room temperature, an electroluminescence circular polarization of approximately 8% is measured under an applied 1 T out-of-plane magnetic field in a surface-emitting geometry. After considering contributions from the Zeeman effect and magnetic circular dichroism, about 6% circular polarization is attributed to the pure spin injection into GaN. This work is focused on the detailed structural and interface characterization of the spin-LED and allows to understand its spin and optoelectronic properties. These results highlight the potential of GaN-based spin-optoelectronic devices compatible with Si platforms.

Aluminum nitride (AlN)-based acoustic filters are key devices of radio-frequency communications. However, the performance of electroacoustic resonators remains limited by the crystalline quality of the piezoelectric AlN material. An innovative material strategy that combines different types of materials (2D and 3D materials) and growth techniques is presented here to enhance the crystalline quality of thick AlN films grown on silicon-based substrates. Building upon previous works showing the efficacy of 2D MoS2 in sputtered-AlN texturing, this paper demonstrates how an in situ thermochemical treatment of the sputtered-AlN/MoS2 seed layers succeeded by a metal organic vapor phase epitaxy (MOVPE) AlN regrowth significantly enhances the crystalline quality of the AlN layer and avoids the detrimental stack delamination at the weak AlN/MoS2 interface. This paper shows that a delicate balance in the thickness of the sputtered-AlN film should be found to facilitate species diffusion toward the underlying MoS2 without compromising its texturizing properties for the subsequent MOVPE AlN regrowth. The sputtered-AlN/MoS2 seed layers involve a nanometric AlN film of less than 5 nm deposited onto three monolayers of MoS2. The heat treatment induces an unexpected chemical and structural nanometric reorganization at the interface, converting the initial lamellar MoS2 film into a discontinuous covalently bonded MoNxOy film, followed by the appearance of metallic Mo nanoparticles at an elevated temperature. Subsequent MOVPE AlN regrowth on the annealed seed layer stacks enables the growth of thick AlN films of up to 600 nm with a mosaicity of less than 0.3 degrees without delamination or cracks. This approach not only facilitates the integration of thick AlN films on Si-based wafers but also opens avenues for growing III-N or other 3D materials on Si through the intercalation of 2D materials.

To fabricate native and monolithic full color micro-displays with a pixel pitch below 10 µm, the three primary colors should be achieved with the InGaN alloy. The prerequisite is to get an efficient red emission with thin InxGa1-xN quantum well (QW) width and an In content of 35%. However, the In content is limited to 25% when grown on GaN. A full InGaN structure combined with different types of relaxed InGaN pseudo-substrates are used to reduce the strain in the active zone. Red electroluminescence was obtained until 650 nm. Homogeneous red emitting InGaN based QWs were also demonstrated.

In this paper, we investigate the Al2O3/GaN critical buried interface of the next generation of gallium nitride (GaN)‐based transistors using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and hard X‐ray photoelectron spectroscopy (HAXPES). Results highlight that gallium oxidation at this interface is enhanced when increasing the Al2O3 thickness from 3 up to 20 nm. Gallium oxidation is reduced when using both O3 and H2O as oxidant precursors, compared with only H2O during the growth of Al2O3. In addition, the O3/H2O‐based Al2O3 favors a reduction of contaminants such as hydrogen and carbon but enhances the presence of halides (Cl− and F−) at this Al2O3/GaN interface.

AbstractFull color micro-displays with a pixel pitch of below 10 µm are needed for augmented and virtual reality applications. In the native emission approach, high efficiency Red-Green-Blue (RGB) pixels could be achieved using monolithically integrated InGaN based micro-LEDs. Here, we report the growth of high optical quality RGB InGaN/InGaN quantum wells grown on InGaN nanopyramids of diameter less than 1 µm by metal organic vapor phase epitaxy. We synthesized the nanopyramids by nanoselective area growth using an in situ patterned epitaxial graphene on SiC as an embedded mask. The RGB emission properties at different locations on the sample are dependent on the size of the InGaN nanopyramids. Advanced correlative analysis conducted on the same transmission electron microscopy lamella reveal a fully or at least nearly relaxed In0.13Ga0.87N core and very regular quantum wells emitting in the red range (620 nm) along the pyramid sidewalls with an In content up to 40%.

Colloidal InSb quantum dots (QDs) are a potential alternative to toxic Pb- and Hg-chalcogenide QDs for covering the technologically important near-infrared/shortwave infrared (NIR/SWIR) spectral range. However, appropriate Sb precursors are scarce and obtaining narrow size distributions is challenging. Tris(dimethylamido)antimony (Sb(NMe2)3) is an appealing choice due to its commercial availability and non-pyrophoric character but implies the reduction of antimony from the +3 to the required -3 state. In reported works, strong reducing agents such as lithium triethylborohydride are used, which lead to the fast co-reduction of both Sb3+ and In3+. The downsides of this approach are reproducibility issues and the risk of forming metal nanoparticles due to the different reduction kinetics of Sb3+ and In3+. Here, indium(I) halides are explored as simultaneous indium source and mild reducing agent for the antimony precursor. The wavelength of the excitonic absorption peak of the phase-pure InSb QDs obtained with this approach can be tuned from 630 to 1890 nm, which corresponds to a size range of approximate to 2-7 nm. The synthesis can also be conducted in a heat-up manner, which facilitates the scale-up and paves the way for the use of InSb QDs in applications such as NIR/SWIR photodetectors, cameras, biological imaging, and telecommunications. A method for the preparation of colloidal InSb quantum dots of low size distribution is presented using indium(I) halides and tris(dimethylamido)antimony as precursors. The size can be controlled in a broad range giving access to an excitonic absorption feature tunable from 630 to 1890 nm. image

In the pursuit of ultrathin and highly sensitive photodetectors, a promising approach involves leveraging the combination of light-sensitive two-dimensional (2D) semiconducting transition-metal dichalcogenides, such as MoS2 and the high electrical conductivity of graphene. Over the past decade, exfoliated 2D materials and electron-beam lithography have been used extensively to demonstrate feasibility on single devices. But for these devices to be used in the real-world systems, it is necessary to demonstrate good device performance similar to lab-based devices with repeatability of the results from device to device and a path to large scale manufacturing. To work in this way, a fabrication process of MoS2/graphene vertical heterostructures with a wafer-scale integration in a CMOS compatible foundry environment is evaluated here. Large-scale atomic layer deposition on 8 inch silicon wafers is used for the growth of MoS2 layers which are then transferred on a 4 inch graphene-based wafer. The MoS2/graphene phototransistors are fabricated collectively, achieving a minimum channel length of 10 mu m. The results measured on dozen of devices demonstrate a photoresponsivity of 50 A W-1 and a remarkable sensitivity as low as 10 nW at 660 nm. These results not only compete with lab-based photodetectors made of chemical vapor deposition grown MoS2 layers transferred on graphene, but also pave the way for the large-scale integration of these emerging 2D heterostructures in optoelectronic devices and sensors.

In this work we present the effect of inductively coupled plasma reactive ion etching (ICP-RIE) combined with atomic layer etching (ALE) on the Al2O3/GaN interface for MOSc-HEMT devices. Time of flight secondary ion mass spectrometry (ToF-SIMS) and hard x-ray photoelectron spectroscopy (HAXPES) highlight an increase of the N/Ga ratio near the interface after etching. ToF-SIMS profiles also show the presence of impurities (H, C, B) at this interface. Atomic force microscopy (AFM) also illustrates a change of the GaN surface morphology for the etched sample.

This scientific paper describes the chemical study of different Al2O3/GaN interfaces found in the new generation of high electron mobility transistors developed for power electronics applications. The stake for these interfaces is the limitation, ideally the absence of an oxidized gallium layer hampering the good electrical behavior of the semiconductor. These structures have been studied through time-of-flight secondary ion mass spectrometry (ToF-SIMS), magnetic SIMS (M-SIMS), and atomic force microscopy (AFM) analyses. Two structures were considered: a bilayer Al2O3 10 nm–GaOx 2 nm on GaN and a Al2O3 10 nm single layer deposited on preliminary etched GaN. The first sample was used as a dedicated reference sample where an actual gallium oxide layer was grown, whereas the second one was a technologically relevant structure. Several experimental conditions were compared for the ToF- and M-SIMS analyses; in particular, three angles of incidence for the primary Cs+ sputter beam (65°, 61°, 45°) were used, leading to diverse depth resolutions and roughnesses, as revealed by surface topography analysis provided by AFM. Among the different incidence angles, it was found that the best experimental conditions were those obtained by ToF-SIMS analysis with an incidence angle of 45°, generating the least roughness.

Graphene/lead sulfide (PbS) quantum dot (QD) hybrid infrared photodetectors have gained a lot of attention in recent times due to their high resolution and cost effective fabrication process. In spite of exhibiting remarkably high responsivity, such hybrid detectors are slow as a result of their internal gain mechanism process. In this work, we present a convenient strategy to modulate the correlation between their responsivity and response time giving access to high resolution fast photodetectors in the broadband wavelength range for imaging purpose. Using a layer-by-layer deposition technique including simultaneous ligand exchange and surface passivation at each layer, homogeneous PbS QD films on chemical vapour deposition grown single layer graphene could be achieved. The obtained hybrid phototransistors exhibit a high responsivity of 108A W-1and sensitivity down to 0.1 pW incident light power in the near-infrared wavelength range. By modulating the incident light at a modulation frequency up to 50 kHz, we achieve a response time as low as 5μs while preserving a much higher responsivity (144 A W-1) compared to existing commercial room temperature infrared photodetectors.

Layered semiconductor gallium selenide (GaSe) is considered a potential candidate for optoelectronic applications because of its direct band gap. Monocrystalline material is, however, a prerequisite to fully exploit these properties in devices, where one-dimensional nano-objects could be considered as a model system. As a consequence of their large surface-to-volume ratio, nano-objects such as nanoribbons are interesting for photodetection applications. Here, we report the vapor-liquid-solid growth of GaSe nanoribbons by MOCVD on 300 mm silicon substrates. A growth model is proposed on the basis of a comprehensive study of the impact of the growth parameters on the nanoribbon morphology. The nanoribbon microstructure is investigated by HR-STEM and Raman spectroscopy characterizations. HR-STEM and TEM cross-sectional observations coupled with EDX analyses reveal a monocrystalline nanoribbon core covered with a native gallium-oxide shell. Test devices are made by contacting individual nanoribbon. The current versus voltage (I-V) characteristic obtained over a range of temperature (-50 to 100 degrees C) in the dark and under white light illumination is fitted on the basis of a back-to-back Schottky diode model. A stable and repeatable dynamic photoresponse is measured from the GaSe nanoribbons, with an I-ON/I-OFF ratio of 17 at room temperature.

Decreasing the thickness of semiconductors to the few monolayer limit often results in structural relaxation and the appearance of new properties. Herein, the bistability of 2ML thick CdTe, where the zinc blende structure of the bulk phase is metastable and the stable (ground) state is represented by an inverted structure with Cd atoms sandwiched by Te planes, is demonstrated. The thermodynamic stability of both phases is demonstrated by the absence of imaginary modes in the phonon dispersion spectra of both phases fully relaxed at 0 K. Both phases are direct‐gap semiconductors and the transformation from the zinc blende phase to the inverted phase is accompanied by a marked increase of the bandgap from 0.13 to 1.03 eV. In combination with the stable α‐CdTe phase, results demonstrate the polymorphism of ultrathin CdTe. A pronounced property contrast between the phases suggests the possible use of few‐monolayer CdTe for memory applications.

The introduction of magnetism in two-dimensional (2D) materials represents an intense field of research nowadays and the quest to reach above-room-temperature ordering temperatures is still underway. intrinsic ferromagnetism was discovered in 2017 in CrI3 and Cr2Ge2Te6 in the monolayer form with low Curie temperatures. An alternative method to introduce magnetism into conventional 2D materials is substitutional doping with magnetic impurities similarly to three-dimensional diluted magnetic semiconductors. The case of Mn-doped transition metal dichalcogenide (MoS2, MoSe2, WS2, WSe2) monolayers is very interesting because combining out-of-plane ferromagnetism and valley contrast leads to ferrovalley materials. In this work, we focus on the incorporation of Mn in MoSe2 by molecular beam epitaxy on graphene which has been rarely addressed up to now. By using a multiscale characterization approach, we demonstrate that Mn atoms are incorporated into the MoSe2 monolayer up to 5 atomic percent. However, when incorporated into the film, Mn atoms tend to diffuse to the grain edges forming undefined MoxMnySez phase at grain boundaries after completion of the MoSe2 monolayer. This segregation leaves the crystalline and electronic structure of MoSe2 unmodified. Above 5%, the saturation of Mn content in MoSe2 leads to the formation of epitaxial MnSe clusters.

Pauline Hauchecorne123 Mickael Martin1, Farzan Gity4, Hanako Okuno5, Jérémy Moeyaert1, Shubhadeep Bhattacharjee4, Bérangère Hyot3, Paul K. Hurley4, Thierry Baron1 1 Univ. Grenoble Alpes, CNRS, CEA/LETI Minatec, LTM, F-38054 Grenoble Cedex, France 2 Univ. Grenoble Alpes, F-38000 Grenoble, France 3 Univ. Grenoble Alpes, CEA-LETI, 17 Avenue des Martyrs, F-38054 Grenoble, France 4 Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork T12 R5CP, Ireland 5 Univ. Grenoble Alpes, CEA, IRIG-MEM, 38000 Grenoble, France pauline.hauchecorne@cea.fr

In this work, the growth of InGaN on epitaxial graphene by molecular beam epitaxy is studied. The nucleation of the alloy follows a three-dimensional (3D) growth mode in the observed temperature range of 515 °C-765 °C, leading to the formation of dendrite-like islands. Careful Raman scattering experiments show that the graphene underneath is not degraded by the InGaN growth. Moreover, lateral displacement of the nuclei during an atomic force microscopy (AFM) scan demonstrates weak bonding interactions between the InGaN and the graphene. Finally, a longer growth time of the alloy gives rise to a compact thin film in a partial epitaxial relationship with the SiC underneath the graphene.

We report on Kelvin probe force microscopy (KPFM) and density functional theory (DFT) investigations of charge transfers in vertical heterojunctions between tungsten diselenide (WSe2) layers and graphene on silicon carbide substrates. The experimental data reveal the existence of an interface dipole, which is shown by DFT to originate from the neutralization of the graphene n-doping by an electron transfer towards the transition metal dichalcogenide (TMD) layer. The relative vacuum level shift probed by KPFM between the TMD and the substrate stays constant when passing from monolayer to bilayer graphene, which confirms that the Schottky-Mott model can be rigorously applied to these interfaces by taking into account the charge transfer from the substrate to the TMD. DFT calculations show that the first TMD layer absorbs almost all the excess charges contained in the graphene, and that the second TMD layer shall not play a significant role in the electrostatics of the system. Negatively charged defect at the TMD edges contribute however to the electrostatic landscape probed by KPFM on both TMD layers.

Semiconductor alloys ZnSnxGe1-xN2 have theoretical crystal structure and electronic structure similar to that of InGaN alloys. These promises of direct and tunable band gaps are very attractive to unlock a suite of functionality for these nitride semiconductors, namely for the use in long wavelength light emitters and light absorbers for solar cells. We report here a structural, electrical and optical investigation of sputtered ZnSnxGe1-xN2 films for 0 <= x <= 1 by gradually substituting germanium with fin. Compared to InGaN alloys which suffer from a miscibility gap and exhibit phase segregation beyond similar to 20% In, ZnSn(x)Ge(1-x)N(2 )form advantageously a continuous alloy for 0 <= x <= 1. Its adjustable lattice parameter a (from 3.22 angstrom to 3.41 angstrom) according to Vegard's law as well as the linear variation of the vibration modes by Fourier transform infrared spectroscopy indicate that the ZnSnxGe1-xN2 alloying is achievable without phase separation. The single chemical environment measured by Mossbauer spectroscopy for Sn4+ ions, whatever Sn content in ZnSnxGe1-xN2, confirms the continuous nature of alloying. Samples exhibit semiconducting properties, including optical band gaps and electronic behaviors with temperature. The experimental observations show that the resistivity in ZnSnxGe1-xN2 alloys can cover several orders of magnitude from a "quasi-metallic" (for ZnSnN2) to a "quasi-insulating" (for ZnGeN2) behavior and that the band gap is tunable from 2.1 eV to 3.04 eV with a nearly linear dependence on the composition. Thus, ZnSnxGe1-xN2 materials offer a solution for bandgap tunability in nitride semiconductors, and may enable enhanced functionality such as efficient green and red light emitters and light absorbers for photosynthetic devices.

Infrared (IR) photodetectors have a wide range of applications in various fields such as telecommunication, thermal imaging, remote sensing, night assistance car driving etc. Combining highly efficient light absorbing nanomaterials with high mobility 2D materials, a new kind of hybrid photodetector has been introduced which dramatically increases the responsivity and gain of the photodetector. Such low dimensional IR phototransistor based on graphene/PbS QD hybrid was first proposed in literature [1, 2] in 2012. Later in 2017, a highresolution broadband image sensor based on such hybrid materials was demonstrated [3], which is sensitive to ultraviolet, visible and infrared light (300–2000 nm).

The Hall effect can be extended by inducing a temperature gradient in lieu of electric field that is known as the Nernst (-Ettingshausen) effect. The recently discovered spin Nernst effect in heavy metals continues to enrich the picture of Nernst effect-related phenomena. However, the collection would not be complete without mentioning the valley degree of freedom benchmarked by the valley Hall effect. Here we show the experimental evidence of its missing counterpart, the valley Nernst effect. Using millimeter-sized WSe _2 mono-multi-layers and the ferromagnetic resonance-spin pumping technique, we are able to apply a temperature gradient by off-centering the sample in the radio frequency cavity and address a single valley through spin-valley coupling. The combination of a temperature gradient and the valley polarization leads to the valley Nernst effect in WSe _2 that we detect electrically at room temperature. The valley Nernst coefficient is in good agreement with the predicted value.