Influence of the reactor environment on the selective area thermal etching of GaN nanohole arrays

Selective area thermal etching (SATE) of gallium nitride is a simple subtractive process for creating novel device architectures and improving the structural and optical quality of III-nitride-based devices. In contrast to plasma etching, it allows, for example, the creation of enclosed features with extremely high aspect ratios without introducing ion-related etch damage. We report how SATE can create uniform and organized GaN nanohole arrays from c-plane and (11–22) semi-polar GaN in a conventional MOVPE reactor. The morphology, etching anisotropy and etch depth of the nanoholes were investigated by scanning electron microscopy for a broad range of etching parameters, including the temperature, the pressure, the NH3 flow rate and the carrier gas mixture. The supply of NH3 during SATE plays a crucial role in obtaining a highly anisotropic thermal etching process with the formation of hexagonal non-polar-faceted nanoholes. Changing other parameters affects the formation, or not, of non-polar sidewalls, the uniformity of the nanohole diameter, and the etch rate, which reaches 6 µm per hour. Finally, the paper discusses the SATE mechanism within a MOVPE environment, which can be applied to other mask configurations, such as dots, rings or lines, along with other crystallographic orientations

Nanoporous GaN by selective area sublimation through an epitaxial nanomask: AlN versus Si x N y

Abstract Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4–0.65 range. The characteristics of these porous layers were compared to those obtained with a Si x N y nanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a Si x N y nanomask were compared

InGaN islands and thin films grown on epitaxial graphene

International audienceIn this work is studied the growth of InGaN on epitaxial graphene by molecular beam epitaxy. The nucleation of the alloy follows a three-dimensional (3D) growth mode, in the explored temperature range of 515-765°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 scan demonstrate weak bonding interactions between InGaN and graphene. Finally, a longer growth time of the alloy gives rise to a compact thin film in partial epitaxial relationship with the SiC underneath the graphene

Growth mode and electric properties of graphene and graphitic phase grown by argon-propane assisted CVD on 3C-SiC/Si and 6H-SiC

The present work is proposing a comparative analysis of the graphitization, achieved by argon-propane assisted chemical vapor deposition, of 6H-SiC(0001) bulk substrates and 3C-SiC heteroepilayers deposited on (111) and (100) silicon. We have investigated the influence of the experimental parameters of the graphitization (pressure, propane flow rate and duration) both on the structural and the electrical properties of the graphitic/graphene phases developed at the samples surface. In particular, the growth mode has been highlighted. It has been shown that, in our experimental conditions, the formation of graphene is only a transitory step followed by a stage of rapid over-deposition of the surface by a highly disordered graphitic phase. This can be understood by a surface chemical potential variation accompanied by a balance between some mass transport at the surface (which could include sublimation) and a deposition regime. It shows that the process time must be properly adjusted to conserve the graphene at the surface. Furthermore, it is shown that the graphene sheet resistance is significantly dependent on the surface uniformity and can be tuned by varying the process pressure

Role of magnetic polarons in ferromagnetic GdN

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