arXiv subjects

Huaide Zhang

Publications and source records attributed to Huaide Zhang.

5 recordsLinked to original sources

arXiv2026

Two-step growth of (In,Ga)N pseudo-substrates on GaN templates by plasma-assisted molecular beam epitaxy

(In,Ga)N layers are grown by plasma-assisted molecular beam epitaxy on GaN templates. We introduce a two-step protocol that involves switching the growth conditions from initially N-stable to metal-stable. Reflection high-energy electron diffraction as well as scanning electron and atomic force microscopy reveal that the first step results in a rough intermediate surface with open pits, whereas the final surface is smooth. The narrow linewidth of the photoluminescence band indicates an excellent compositional homogeneity of the upper layer. Its in-plane lattice constant is determined to be $\approx$3.26 Åfrom X-ray diffraction measurements. This combination of favorable properties makes these layers attractive as pseudo-substrates for the growth of red-emitting (In,Ga)N light-emitting diodes. In particular, the approach presented here does not require any complex external processing and is, thus, scalable and economical.

cond-mat.mtrl-sci↗

arXiv2026

Simultaneously monitoring Ga adsorption and desorption kinetics on GaN(0001) using four in situ techniques

We present a systematic investigation of Ga adsorption and desorption kinetics on the wurtzite GaN(0001) surface using four in situ techniques operated simultaneously: reflection high-energy electron diffraction, laser reflectometry, line-of-sight quadrupole mass spectrometry, and optical pyrometry. Flux- and temperature-dependent experiments are performed for Ga coverages ranging from the submonolayer to the droplet regime. Despite their distinct transient responses, the signals from all four techniques and their trends with surface coverage are quantitatively reproduced by a unified kinetic model of Ga adsorption, diffusion, and desorption. An Arrhenius analysis of the Ga adlayer desorption yields an activation energy of (2.87 $\pm$ 0.04) eV.

physics.app-ph↗

arXiv2025

Fabrication of (In,Ga)N pseudo-substrates by a three-step growth protocol without ex-situ processing

We fabricate (In,Ga)N pseudo-substrates with a total thickness of ~1 um grown on GaN templates using plasma-assisted molecular beam epitaxy. In a three-step process, we change growth conditions from N-rich to metal-rich in order to sequentially form a roughened GaN layer, relaxed (In,Ga)N nanostructures, and a coalesced, smooth (In,Ga)N layer. Samples are analyzed by scanning electron and atomic force microscopy, X-ray diffraction, as well as photo- and cathodoluminescence spectroscopy. Compared to a reference layer grown directly on GaN, the pseudo-substrate exhibits a higher In content (~0.3), strain relaxation degree (~80%), narrower photoluminescence linewidth, and larger area fraction of bright regions in cathodoluminescence maps, showing the benefits of the three-step growth protocol. This straightforward approach does not necessitate any ex-situ processing and could enable the scalable fabrication of (In,Ga)N pseudo-substrates for high-efficiency red-emitting (In,Ga)N devices.

cond-mat.mtrl-sci↗

arXiv2024

Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile suboxide: The examples of Ga and Ge

The delivery of an elemental cation flux to the substrate surface in the oxide molecular beam epitaxy (MBE) chamber has been utilized not only for the epitaxial growth of oxide thin films in the presence of oxygen but also in the absence of oxygen for the growth temperature calibration (by determining the adsorption temperature of the elements) and in-situ etching of oxide layers (e. g., Ga2O3 etched by Ga). These elemental fluxes may, however, leave unwanted cation adsorbates or droplets on the surface, which traditionally require removal by in-situ superheating or ex-situ wet-chemical etching with potentially surface-degrading effects. This study demonstrates a universal in-situ approach to remove the residual cation elements from the surface via conversion into a volatile suboxide by a molecular O2-flux in an MBE system followed by suboxide evaporation at temperatures significantly below the elemental evaporation temperature. We experimentally investigate the in-situ etching of Ga and Ge cation layers and their etching efficiency using in-situ line-of-sight quadrupole mass spectrometry (QMS) and reflection high-energy electron diffraction (RHEED). The application of this process is demonstrated by the in-situ removal of residual Ga droplets from a SiO2 mask after structuring a Ga2O3 layer by in-situ Ga-etching. This approach can be generally applied in MBE and MOCVD to remove residual elements with vapor pressure lower than that of their suboxides, such as B, In, La, Si, Sn, Sb, Mo, Nb, Ru, Ta, V, and W.

cond-mat.mtrl-sci↗

arXiv2023

Machine learning-enabled tomographic imaging of chemical short-range atomic ordering

In solids, chemical short-range order (CSRO) refers to the self-organisation of atoms of certain species occupying specific crystal sites. CSRO is increasingly being envisaged as a lever to tailor the mechanical and functional properties of materials. Yet quantitative relationships between properties and the morphology, number density, and atomic configurations of CSRO domains remain elusive. Herein, we showcase how machine learning-enhanced atom probe tomography (APT) can mine the near-atomically resolved APT data and jointly exploit the technique's high elemental sensitivity to provide a 3D quantitative analysis of CSRO in a CoCrNi medium-entropy alloy. We reveal multiple CSRO configurations, with their formation supported by state-of-the-art Monte-Carlo simulations. Quantitative analysis of these CSROs allows us to establish relationships between processing parameters and physical properties. The unambiguous characterization of CSRO will help refine strategies for designing advanced materials by manipulating atomic-scale architectures.

cond-mat.mtrl-sci↗