arXiv subjects

Junlei Zhao

Publications and source records attributed to Junlei Zhao.

25 records · Page 2Linked to original sources

arXiv2023

Orientation-Dependent Atomic-Scale Mechanism of $β$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ Thin Film Epitaxial Growth

$β$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ has gained intensive interests of research and application as an ultrawide bandgap semiconductor. Epitaxial growth technique of the $β$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ thin film possesses a fundamental and vital role in the $\mathrm{Ga}_{2}\mathrm{O}_{3}$-based device fabrication. In this work, epitaxial growth mechanisms of $β$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ with four low Miller-index facets, namely (100), (010), (001), and ($\overline{2}$01), are systematically explored using large-scale machine-learning molecular dynamics simulations at the atomic scale. The simulations reveal that the migration of the face-centered cubic stacking O sublattice plays a predominant role in rationalizing the different growth mechanisms between (100)/(010)/(001) and ($\overline{2}$01) orientations. The resultant complex combinations of the stacking faults and twin boundaries are carefully identified, and shows a good agreement with the experimental observation and ab initio calculation. Our results provide useful insights into the gas-phase epitaxial growth of the $β$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ thin films and suggest possible ways to tailor its properties for specific applications.

cond-mat.mtrl-sci↗

arXiv2023

Universal radiation tolerant semiconductor

Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta double polymorph Ga2O3 structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in gamma-Ga2O3. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the beta-to-gamma Ga2O3 transformation, as a function of the increased disorder in beta-Ga2O3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that gamma/beta double polymorph Ga2O3 structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors.

cond-mat.mtrl-sci↗

arXiv2023

Complex $\mathrm{Ga}_{2}\mathrm{O}_{3}$ Polymorphs Explored by Accurate and General-Purpose Machine-Learning Interatomic Potentials

$\mathrm{Ga}_{2}\mathrm{O}_{3}$ is a wide-bandgap semiconductor of emergent importance for applications in electronics and optoelectronics. However, vital information of the properties of complex coexisting $\mathrm{Ga}_{2}\mathrm{O}_{3}$ polymorphs and low-symmetry disordered structures is missing. In this work, we develop two types of kernel-based machine-learning Gaussian approximation potentials (ML-GAPs) for $\mathrm{Ga}_{2}\mathrm{O}_{3}$ with high accuracy for $β$/$κ$/$α$/$δ$/$γ$ polymorphs and generality for disordered stoichiometric structures. We release two versions of interatomic potentials in parallel, namely soapGAP and tabGAP, for excellent accuracy and exceeding speedup, respectively. We systematically show that both the soapGAP and tabGAP can reproduce the structural properties of all the five polymorphs in an exceptional agreement with ab initio results, meanwhile boost the computational efficiency with $5\times10^{2}$ and $2\times10^{5}$ computing speed increases compared to density functional theory, respectively. The results show that the liquid-solid phase transition proceeds in three different stages, a "slow transition", "fast transition" and "only Ga migration". We show that this complex dynamics can be understood in terms of different behavior of O and Ga sublattices in the interfacial layer.

cond-mat.mtrl-sci↗

arXiv2022

Lattice-aligned gallium oxynitride nanolayer for GaN surface enhancement and function extension

Gallium nitride (GaN), as a promising alternative semiconductor to silicon, is of well-established use in photoelectronic and electronic technology. However, the vulnerable GaN surface has been a critical restriction that hinders the development of GaN-based devices, especially regarding device stability and reliability. Here, we overcome this challenge by converting the GaN surface into a gallium oxynitride (GaON) epitaxial nanolayer through an in-situ two-step "oxidation-reconfiguration" process. The oxygen plasma treatment overcomes the chemical inertness of the GaN surface, and the sequential thermal annealing manipulates the kinetic-thermodynamic reaction pathways to create a metastable GaON nanolayer with wurtzite lattice. This GaN-derived GaON nanolayer is a tailored structure for surface reinforcement and possesses several advantages, including wide bandgap, high thermodynamic stability, and large valence band offset with GaN substrate. These enhanced physical properties can be further leveraged to enable GaN-based applications in new scenarios, such as complementary logic integrated circuits, photoelectrochemical water splitting, and ultraviolet photoelectric conversion, making GaON a versatile functionality extender.

physics.app-ph↗

arXiv2021

Two-dimensional Ferroelectric Ga2O3 Bilayers with Unusual Strain-engineered Interlayer Interactions

Two-dimensional (2D) van der Waals (vdW) materials and their bilayers have stimulated enormous interests in fundamental researches and technological applications. Recently, a group of 2D vdW III2-VI3 materials with out-of-plane ferroelectricity have attracted substantial attentions. In this work, the structural, electronic and optical properties of 2D ferroelectric Ga2O3 bilayer system are systematically studied using ab-initio computational method. Intrinsic dipoles of the two freestanding monolayers lead to three distinct dipole models (one ferroelectric and two antiferroelectric models). The stable stacking configurations of ferroelectric and antiferroelectric dipole models can be transferred with polarization reversal transition of the monolayers without additional operation. Interlayer perturbation effects combined with biaxial-strain engineering lead to high tunablility of the electronic and optical properties of the bilayer systems. Surprisingly, the results reveal a phase transition from vdW to ionic interlayer interaction induced by in-plane biaxial tensile strain. Detailed analyses suggest a transition mechanism based on the ionic bonding nature of the Ga2O3 system, involving interlayer rearrangement of anions to compensate the symmetry breaking of the heavily distorted ionic folding configurations. These insights can open new prospects for future experimental synthesis, characterization and application of 2D Ga2O3 atomic-thin layered systems.

cond-mat.mtrl-sci↗

arXiv2021

Phase Transition of Two-Dimensional Ferroelectric and Paraelectric Ga2O3 Monolayer: A Density Functional Theory and Machine-Learning Study

Ga2O3 is a wide-band-gap semiconductor of great interest for applications in electronics and optoelectronics. Two-dimensional (2D) Ga2O3 synthesized from top-down or bottom-up processes can reveal brand new heterogeneous structures and promising applications. In this paper, we study phase transitions among three low-energy stable Ga2O3 monolayer configurations using density functional theory and a newly developed machine-learning Gaussian approximation potential, together with solid-state nudged elastic band calculations. Kinetic minimum energy paths involving direct atomic jump as well as concerted layer motion are investigated. The low phase transition barriers indicate feasible tunability of the phase transition and orientation via strain engineering and external electric fields. Large-scale calculations using the newly trained machine-learning potential on the thermally activated single-atom jumps reveal the clear nucleation and growth processes of different domains. The results provide useful insights to future experimental synthesis and characterization of 2D Ga2O3 monolayers.

cond-mat.mtrl-sci↗

arXiv2018

Migration barriers for surface diffusion on a rigid lattice: challenges and solutions

Atomistic rigid lattice Kinetic Monte Carlo is an efficient method for simulating nano-objects and surfaces at timescales much longer than those accessible by molecular dynamics. A laborious part of constructing any Kinetic Monte Carlo model is, however, to calculate all migration barriers that are needed to give the probabilities for any atom jump event to occur in the simulations. One of the common methods of barrier calculations is Nudged Elastic Band. The number of barriers needed to fully describe simulated systems is typically between hundreds of thousands and millions. Calculations of such a large number of barriers of various processes is far from trivial. In this paper, we will discuss the challenges arising during barriers calculations on a surface and present a systematic and reliable tethering force approach to construct a rigid lattice barrier parameterization of face-centred and body-centred cubic metal lattices. We have produced several different barrier sets for Cu and for Fe that can be used for KMC simulations of processes on arbitrarily rough surfaces. The sets are published as Data in Brief articles and available for the use.

cond-mat.mtrl-sci↗