无斜率选择的分子束外延方程两阶能量稳定的线性格式

针对无斜率选择的分子束外延(Molecular Beam Epitaxy,MBE)模型,考虑了一种新的正则项设计和非线性项外推,得到了一种新的线性求解和能量稳定的数值格式,并从理论上证明了这种格式具有两阶时间精度.数值实验验证了格式的误差精度和能量下降等性质.

Magneto-transport properties of the off-stoichiometric Co_2MnAl film epitaxially grown on GaAs(001)

We have investigated the magneto-transport properties of an off-stoichiometric full-Heusler alloy Co_2MnAl single-crystalline film. The Co_(1.65)Mn_(1.35)Al(CMA) film epitaxially grown on Ⅲ–Ⅴ semiconductor GaAs substrate exhibits perpendicular magnetic anisotropy. The resistivity of the CMA film increases with the temperature T decreasing from 300 to 5 K, showing a semiconducting-like transport behavior. Different activation energies are found in three temperature regions with transition temperatures of 35 and 110 K. In the meanwhile, the remanent magnetization can be described by T^(3/2) and T^2 laws in the corresponding medium and high T ranges, respectively. The transition at around 110 K could be attributed to the ferromagnetism evolving from localized to itinerant state. The Curie temperature of the CMA film is estimated to be ～640 K. The intrinsic anomalous Hall conductivity of ～55 Ω^(-1) cm^(-1) is obtained, which is almost twenty times smaller than that of Co_2MnAl.

Non-Selective SiGe Graphic Epitaxial by MBE

To handle the thermal budget in SiGe BiCMOS process, a non-selective graphic epitaxial technology using molecular beam epitaxial （MBE） has been developed. SEM, AFM, XRD, and dislocation density measurements are carried out. The SiGe film＇s RMS roughness is 0.45nm, and dislocation density is 0.3×10^3cm^-2-1.2×10^3cm^-2. No dislocation accumulation exists on the boundary of the windows; this indicates the high quality of the SiGe film. The experiment results show that the technology presented in this paper meets the fabrication requirements of SiGe BiCMOS.

Recent progress on borophene： Growth and structures

Boron is the neighbor of carbon on the periodic table and exhibits unusual physical characteristics derived from electron-deficient, highly delocalized covalent bonds. As the nearest neighbor of carbon, boron is in many ways similar to carbon, such as having a short covalent radius and the flexibility to adopt sp2 hybridization. Hence, boron could be capable of forming monolayer structural analogues of graphene. Although many theoretical papers have reported finding two-dimensional allotropes of boron, there had been no experimental evidence for such atom-thin boron nanostructures until 2016. Recently, the successful synthesis of single-layer boron （referred to as borophene） on the Ag（lll） substrate opens the era of boron n-nostructures. In this brief review, we will discuss the progress that has been made on borophene in terms of synthetic techniques, characterizations and the atomic models. However, borophene is just in infancy; more efforts are expected to be made in future on the controlled synthesis of quality samples and tailoring its physical properties.

Diameter evolution of selective area grown Ga-assisted GaAs nanowires

Tapering of vapour-liquid-solid （VLS） grown nanowires （NWs） is a widespread phenomenon resulting from dynamics of the liquid droplet during growth and direct vapour-solid （VS） growth on the sidewall. To investigate both effects in a highly controlled wa35 we developed a novel two-step growth approach for the selective area growth （SAG） of GaAs nanowires （NWs） by molecular beam epitaxy. In this growth approach optimum growth parameters are provided for the nucleation of NWs in a first step and for the shape variation during elongation in a second step, allowing NWs with a thin diameter （45 nrn） and an untapered morphology to be realized with high vertical yield. We quantify the flux dependence of radial VS growth and build a model that takes into account diffusion on the NW sidewalls to explain the observed VS growth rates. As our model is consistent with axial VLS growth we can combine it with an existing model for the diameter variation due to the droplet dynamics at the NW top. Thereby, we achieve full understanding of the diameter of NWs over their entire length and the evolution of the diameter and tapering during growth. We conclude that only the combination of droplet dynamics and VS growth results in an untapered morphology. This result enables NW shape engineering and has important implications for doping of NWs.

Gate length dependent transport properties of in-plane core-shell nanowires with raised contacts

Three-dimensional(3D)nanoscale crystal shaping has become essential for the precise design of advanced electronic and quantum devices based on electrically gated transport.In this context,Ⅲ-Ⅴ semiconductor-based nanowires with low electron effective mass and strong spin-orbit coupling are particularly investigated because of their exceptional quantum transport properties and the good electrostatic control they provide.Among the main challenges involved in the processing of these nanodevices are(i)the management of the gate stack which requires ex-situ passivation treatment to reduce the density of traps at the oxide/semiconductor interface,(ii)the ability to get good ohmic contacts for source and drain electrodes and(iii)the scalability and reliability of the process for the fabrication of complex architectures based on nanowire networks.In this paper,we show that selective area molecular beam epitaxy of in-plane InGaAs/InP core-shell nanowires with raised heavily doped source and drain contacts can address these different issues.Electrical characterization of the devices down to 4 K reveals the positive impact of the InP shell on the gate electrostatic control and effective electron mobility.Although comparable to the best reported values for In(Ga)As nanostructures grown on InP,this latter is severely reduced for sub-100 nm channel highlighting remaining issue to reach the ballistic regime.