Molecular Beam Epitaxy Growth of Tetragonal FeS Films on SrTiO3(001) Substrates

We report the successful growth of the tetragonal FeS film with one or two unit-cell （UC） thickness on SrTiO33（001） substrates by molecular beam epitaxy. Large lattice constant mismatch with the substrate leads to high density of defects in single-UC FeS, while it has been significantly reduced in the double-UC thick film due to the lattice relaxation. The scanning tunneling spectra on the surface of the FeS thin film reveal the electronic doping effect of single-UC FeS from the substrate. In addition, at the Fermi level, the energy gaps of approximately 1.5？meV are observed in the films of both thicknesses at 4.6？K and below. The absence of coherence peaks of gap spectra may be related to the preformed Cooper-pairs without phase coherence.

Molecular Beam Epitaxy Growth and Scanning Tunneling Microscopy Study of Pyrite CuSe2 Films on SrTiO3

We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide （CuSe2 ） films on SrTiO3 （001）. Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the Stranski-Krastanov （layer-plus-island） mode with a preferential orientation of （111）. Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2 ×√3 and √x ×√3-R30°. The Cu termi- nation is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.

Development of in situ characterization techniques in molecular beam epitaxy

Ex situ characterization techniques in molecular beam epitaxy(MBE)have inherent limitations,such as being prone to sample contamination and unstable surfaces during sample transfer from the MBE chamber.In recent years,the need for improved accuracy and reliability in measurement has driven the increasing adoption of in situ characterization techniques.These techniques,such as reflection high-energy electron diffraction,scanning tunneling microscopy,and X-ray photoelectron spectroscopy,allow direct observation of film growth processes in real time without exposing the sample to air,hence offering insights into the growth mechanisms of epitaxial films with controlled properties.By combining multiple in situ characterization techniques with MBE,researchers can better understand film growth processes,realizing novel materials with customized properties and extensive applications.This review aims to overview the benefits and achievements of in situ characterization techniques in MBE and their applications for material science research.In addition,through further analysis of these techniques regarding their challenges and potential solutions,particularly highlighting the assistance of machine learning to correlate in situ characterization with other material information,we hope to provide a guideline for future efforts in the development of novel monitoring and control schemes for MBE growth processes with improved material properties.

High Lattice Match Growth of InAsSb Based Materials by Molecular Beam Epitaxy

High lattice match growth of InAsSb based materials on GaSb substrates is demonstrated. The present results indicate that a stable substrate temperature and the optimal flux ratios are of critical importance in achieving a homogeneous InAsSb based material composition throughout the growth period. The quality of these epilayers is assessed using a high-resolution x-ray diffraction and atomic force microscope. The mismatch between the GaSb substrate and InAsSb alloy achieves almost zero, and the rms surface roughness of InAsSb alloy achieves around 1.7A over an area of 28μm × 28μm. At the same time, the mismatches between GaSb and InAs/InAs0.73Sb0.27 superlattices （SLs） achieve approximately 100 arcsec （75 periods） and zero （300 periods）, with the surface rms roughnesses of InAs/InAs0.73Sb0.27 SLs around 1.8 A （75 periods） and 2.1A （300 periods） over an area of 20 μm×20 μm, respectively. After fabrication and characterization of the devices, the dynamic resistance of the n-barrier-n InAsSb photodetector near zero bias is of the order of 10^6Ω·cm^2. At 77K, the positive-intrinsic-negative photodetectors are demonstrated in InAsSb and InAs/InAsSb SL （75 periods） materials, exhibiting fifty-percent cutoff wavelengths of 3.8μm and 5.1μm, respectively.

Epitaxial growth triggered core-shell Pd@RuP nanorods for high-efficiency electrocatalytic hydrogen evolution

Ru with Pt-like hydrogen bond strength,knockdown cost(~1/3 of Pt),and eximious stability is a competitive replacement for Pt-based catalysts towards the hydrogen evolution reaction(HER)in water splitting.The design of Ru-based catalysts via interface construction,crystal phase control,and specific light element doping to realize the impressive promotion of limited activity and stability remains challenging.Herein,we report the fabrication of Pd@RuP core-shell nanorods(NRs)via an epitaxial growth method,where ultrathin RuP shells extend the face-centered cubic(fcc)crystal structure and(111)plane of the Pd NRs core.Density functio nal theory results confirm that the core-s hell interface engineering and P doping synergistically accelerate electron transfer and moderate the d-band center to generate a suitable affinity for H*,thus optimizing HER kinetics.Compared with Pd@Ru NRs and Pt/C,the Pd@RuP NRs exhibit preferable electrocatalytic stability and superior activity with a low overpotential of 18 mV at 10 mA cm-2in the alkaline HER process.Furthermore,the integrated Pd@RuP//RuO2-based electrolyzer also displays a low operation potential of 1.42 V to acquire 10 mA cm-2,demonstrating great potential for practical water electrolysis.Our work presents an efficient avenue to design Ru-based electrocatalysts via epitaxial growth for extraordinary HER performance.

Epitaxial growth of trilayer graphene moiré superlattice

The graphene-based moiré superlattice has been demonstrated as an exciting system for investigating strong correlation phenomenon. However, the fabrication of such moiré superlattice mainly relies on transfer technology. Here, we report the epitaxial growth of trilayer graphene(TLG) moiré superlattice on hexagonal boron nitride(h BN) by a remote plasma-enhanced chemical vapor deposition method. The as-grown TLG/h BN shows a uniform moiré pattern with a period of ~ 15 nm by atomic force microscopy(AFM) imaging, which agrees with the lattice mismatch between graphene and h BN. By fabricating the device with both top and bottom gates, we observed a gate-tunable bandgap at charge neutral point(CNP) and displacement field tunable satellite resistance peaks at half and full fillings. The resistance peak at half-filling indicates a strong electron–electron correlation in our grown TLG/h BN superlattice. In addition, we observed quantum Hall states at Landau level filling factors ν = 6, 10, 14,..., indicating that our grown trilayer graphene has the ABC stacking order. Our work suggests that epitaxy provides an easy way to fabricate stable and reproducible two-dimensional strongly correlated electronic materials.

Preface to Special Issue on Towards High Performance Ga_(2)O_(3) Electronics: Epitaxial Growth and Power Devices(Ⅰ)

There is currently great optimism within the electronics community that gallium oxide(Ga_(2)O_(3)) ultra-wide bandgap semiconductors have unprecedented prospects for eventually revolutionizing a rich variety of power electronic applications. Specially, benefiting from its ultra-high bandgap of around 4.8 eV, it is expected that the emerging Ga_(2)O_(3) technology would offer an exciting platform to deliver massively enhanced device performance for power electronics and even completely new applications.

Epitaxial Growth of 150mm Silicon Epi\|Wafers for Advanced IC Applications

With the device feature's size miniaturization in very large scale integrated circuit and ultralarge scale integrated circuit towards the sub\|micron and beyond level, the next generation of IC device requires silicon wafers with more improved electrical characteristics and reliability as well as a high perfection of the wafer surface. Compared with the polished wafer with a relatively high density of crystal originated defects (e. g. COPs), silicon epi\|wafers can meet such high requirements. The current development of researches on the 150mm silicon epi\|wafers for advanced IC applications is described. The P/P\++ CMOS silicon epi\|wafers were fabricated on a PE2061 Epitaxial Reactor (made by Italian LPE Company). The material parameters of epi\|wafers, such as epi\|defects, uniformity of thickness and resistivity, transition width, and minority carrier generation lifetime for epi\|layer were characterized in detail. It is demonstrated that the 150mm silicon epi\|wafers on PE2061 can meet the stringent requirements for the advanced IC applications.

Growth of Thin Silicon on Sapphire (SOS) Film Materials and Device Applications

The increasing emphasis on the sub\|micron CMOS/SOS devices has placed a demand for high quality thin silicon on sapphire (SOS) films with thickness of the order 100-200nm. It is demonstrated that the crystalline quality of as\|grown thin SOS films by chemically vapor deposition method can be greatly improved by solid phase epitaxy (SPE) process: implantation of self\|silicon ions and subsequent thermal annealing. Subsequent regrowth of this amorphous layer leads to a great improvement in silicon layer crystallinity and channel carrier mobility, respectively by double crystal X\|ray diffraction and electrical measurements. Thin SPE SOS films would have application to the high\|performance CMOS circuitry.

Three-dimensionally oriented organization of hexagonal MIL-96 microplates toward superior film microstructure

Preferential orientation control of metal—organic framework(MOF)films is advantageous for maximizing pore uniformity and minimizing grain-boundary defects.Nonetheless,the preparation of MOF films with both in-plane and out-of-plane orientations remains a grand challenge.In this study,we reported the preparation of three-dimensionally oriented MIL-96 layers through combining morphology control of MIL-96 seeds with addition of polyvinylpyrrolidone surfactants and arachidonic acids.The three-dimensionally oriented MIL-96 film was readily obtained through in-plane epitaxial growth.It is anticipated that the aforementioned protocol can be effective for obtaining diverse MOF films with a three-dimensionally oriented organization.

Heteroepitaxy and Kinetic Study of GaAs/Ge/GaAs Multilayer Material

GaAs/Ge/GaAs multilayer heterostructure material has been prepared in situ in chloride system with improved double bubble bottle and double reaction chamber. In order to control the growth process, the effect of various parameters on the growth rate of heteroepitaxy of GaAs on Ge substrate (GaAs/Ge) and that of Ge on GaAs substrate (Ge/GaAs) has been studied and their growth mechanism discussed. It is found that the growth mechanism of GaAs/Ge is similar to that of GaAs/GaAs, both are controlled by chemical reaction rate on the surface, but the growth rate of the former is much higher than that of latter due to the catalytic effect of Ge. The growth mechanism of Ge/GaAs is temperature dependent. When T around 800 approximately 700°C, it is controlled by diffusion transport and when t < 700°C, it is controlled by surface chemical reaction. On the basis of the growth mechanism study, a good quality GaAs/Ge/GaAs multilayer heterostructure material with smooth surface morphology and sharp interface was prepared under the optimum conditions.

Epitaxial Growth of YBCO Thin Films on LaAlO_3 Substrate with CeO_2 Buffer Layer

By the r. f. magnetron sputtering method, the CeO_2 buffer layers were prepared on (100) LaAlO_3 sub-strates. The results of X-ray diffraction and Ф-scan indicated that the CeO_2 films were unique ( 100)-orientedand epitaxial. The YBa_2Cu_3O_(7-6)(YBCO) films, which were deposited on the CeO_2/LaAlO_3 by d. c. magnetronsputtering, exhibited transition temperatures of 89～91 K,and had critical current densities exceeding 10￣6 A/cm￣2 at 77 K in zero magnetic field.

Epitaxial growth of antimony nanofilms on HOPG and thermal desorption to control the film thickness

Group-V elemental nanofilms were predicted to exhibit interesting physical properties such as nontrivial topological properties due to their strong spin-orbit coupling,the quantum confinement,and surface effect.It was reported that the ultrathin Sb nanofilms can undergo a series of topological transitions as a function of the film thickness h:from a topological semimetal(h>7.8 nm)to a topological insulator(7.8 nm>h>2.7 nm),then a quantum spin Hall(QSH)phase(2.7 nm>h>1.0 nm)and a topological trivial semiconductor(h<1.0 nm).Here,we report a comprehensive investigation on the epitaxial growth of Sb nanofilms on highly oriented pyrolytic graphite(HOPG)substrate and the controllable thermal desorption to achieve their specific thickness.The morphology,thickness,atomic structure,and thermal-strain effect of the Sb nanofilms were characterized by a combination study of scanning electron microscopy(SEM),atomic force microscopy(AFM),and scanning tunneling microscopy(STM).The realization of Sb nanofilms with specific thickness paves the way for the further exploring their thickness-dependent topological phase transitions and exotic physical properties.

The Growth and Microstructure of GaAs Embedded with Al Nanocrystals

The preparation and the microstructure of GaAs embedded with Al nanocrystals prepared by Laser molecular beam epitaxy were investigated.The microstructure of the sample was observed by transmission electron microscope.The reflection high-energy electron diffraction(RHEED)pattern varied from the stripe pattern to the spot pattern at the beginning of the Al nanocrystals growth,and then the spot pattern tended to change to the stripe pattern.There was a large lattice mismatch between Al and GaAs substrate,and Al formed three-dimensional islands on the GaAs substrate,which led to the RHEED transformation into the spot pattern.Otherwise,the dislocations would be formed between the GaAs layer and Al islands due to the large lattice mismatch.Meanwhile,there was some polycrystal of GaAs around the Al islands.

Low Temperature Growth of GaAs on Si byIon Beam Cluster Technique

Ion cluster beam (ICB) technique has many advantages in depositing thin film. In present study some characters of epitaxial layer of GaAs on Si by ICB have been investigated. these include: comparison of crystalline quality between ICB deposited GaAs and vacuum deposited GaAs, and to reveal defects by etching on GaAs-Si interface. The experimental results are discussed.

Effect of Oxygen Partial Pressure on Epitaxial Growth and Properties of Laser-Ablated AZO Thin Films

Al-doped ZnO（AZO） thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures（P_（O2））.The effect of P_（O2） on the crystal structure,preferred orientation as well as the electrical and optical properties of the films was investigated.The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure,showing a significant c-axis orientation.The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P_（O2）.At the optimum oxygen partial pressures of 10- 15 Pa,the AZO thin films were epitaxially grown on c-sapphire substrates with the（0001） plane parallel to the substrate surface,i e,the epitaxial relationship was AZO（000 1） // A1_2O_3（000 1）.With increasing P_（O2）,the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly,which led to an enhancement in electrical conductivity of the AZO thin films.All the films were highly transparent with an optical transmittance higher than 85%.

Review of a direct epitaxial approach to achieving micro-LEDs

There is a significantly increasing demand of developing augmented reality and virtual reality(AR and VR) devices,where micro-LEDs(μLEDs) with a dimension of ≤ 5 μm are the key elements. Typically, μLEDs are fabricated by dry-etching technologies, unavoidably leading to a severe degradation in optical performance as a result of dry-etching induced damages. This becomes a particularly severe issue when the dimension of LEDs is ≤ 10 μm. In order to address the fundamental challenge, the Sheffield team has proposed and then developed a direct epitaxial approach to achievingμLEDs, where the dry-etching technologies for the formation of μLED mesas are not needed anymore. This paper provides a review on this technology and then demonstrates a number of monolithically integrated devices on a single chip using this technology.

Investigation into epitaxial growth optimization of a novel AlGaN/GaN HEMT structure for application in UV photodetectors

In this work,a novel ultraviolet(UV)photodetector(PD)based on AlGaN/u-GaN/p-GaN/u-GaN heterojunction high electron mobility transistor(HEMT)has been developed.This HEMT epilayer is grown using the metal-organic chemical vapor deposition(MOCVD)technique,and the growth parameters,including the AlGaN growth temperature,preheating temperature of the p-GaN layer,and NH3/N2 flow rate,are optimized to improve the quality of the epilayer.The optimized epilayer exhibits a flat surface with a root mean square value of 0.146 nm and low dislocation density.The p-GaN thickness in epitaxial wafers has a significant influence on electrical and UV photoresponse.With a p-GaN of 1µm,the UV PD demonstrates a significant switching ratio and transconductance of 107 and 127.3 mS mm^(-1),respectively.Acting as a UV PD,it also exhibits a high light on/off ratio(I_(light)/I_(dark))of 6.35×10^(5),a high responsivity(R)of 48.11 A W^(-1),and a detectivity(D*)of 6.85×10^(12)Jones under 365-nm UV illumination with light power density of 86.972 mW cm^(-2).The high-performance HEMT and UV detectors,which incorporate p-GaN etchless technology,have been refined through advancements in epitaxial growth and structural design.These improvements solidify the groundwork for large-scale manufacturing of UV communication systems and laser diodes.

A New Process for Improving Performance of VCSELs

A new process method is proposed to improve the light output power of GaAs vertical cavity surface-emitting lasers （VCSELs）. The VCSELs with open-annulus-distributed holes have a light output power 1.34 times higher than those with ring trenches. The 14μm-aperture devices have a light output power higher than 10mW and have a maximum of 12.48mW at 29.6mA. In addition,open-annulus-distributed holes offer bridges for current injection,so the connecting Ti-Au metal between the ohmic contact and bonding pad does not have to cross the ring trench, and it therefore would not cause the connecting metal to be broken. These VCSELs also show high-temperature operation capabilities,and they have a maximum output power of 8mW even at an operation temperature of up to 60℃.

Plasma Treatment Enhanced Magnetic Properties in Manganese Doped Titanium Nitride Thin Films

The ferromagnetic manganese doped TiN films were grown by plasma assisted molecular beam epitaxy on MgO（001） substrates. The nitrogen concentration and the ratio of manganese at Ti lattice sites increase after the plasma annealing post treatment. TIN（002） peak shifts toward low angle direction and TiN（111） peak disappears after the post treatment. The lattice expansion and peak shift are mainly ascribed to the reduction of nitrogen vacancies in films. The magnetism was suppressed in as-prepared sample due to the pinning effect of the nitrogen vacancies at defect sites or interface. The magnetism can be activated by the plasma implantation along with nitrogen vacancies reduce. The decrease of nitrogen vacancies leads to the enhancement of ferromagnetism.