Y. X. Song

Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator

A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current. By exploring the out-of-plane spin texture, we demonstrate spin injection from GaAs to TI and its significant contribution to the surface current, which can be manipulated by an external magnetic field. These discoveries pave the way to not only intriguing new physics but also enriched spin functionalities by integrating TI with conventional semiconductors, such that spin-enabled optoelectronic devices may be fabricated in such hybrid structures.

Structural properties of GeSn thin films grown by molecular beam epitaxy

GeSn thin films on Ge (001) with various Sn concentrations from 3.36 to 7.62% were grown by molecular beam epitaxy and characterized. The structural properties were analyzed by reciprocal space mapping in the symmetric (004) and asymmetric (224) planes by high resolution X-ray diffraction (XRD). The lateral correlation length (LCL) and the mosaic spread (MS) were extracted for the epi-layer peaks in the asymmetric (224) diffraction. With the increase of Sn concentration, the LCL reduces while the MS increases, indicating degrading crystalline quality. Dislocations were observed in the sample with 7.62% Sn concentration by transmission electron microscope, consistent with the strain relaxation found in XRD mapping. Besides, the surface morphologies were investigated.

Effect of thermal annealing on structural properties of GeSn thin films grown by molecular beam epitaxy

GeSn alloy with 7.68% Sn concentration grown by molecular beam epitaxy has been rapidly annealed at different temperatures from 300°C to 800°C. Surface morphology and roughness annealed below or equal to 500°C for 1 min have no obvious changes, while the strain relaxation rate increasing. When the annealing temperature is above or equal to 600°C, significant changes occur in surface morphology and roughness, and Sn precipitation is observed at 700°C. The structural properties are analyzed by reciprocal space mapping in the symmetric (004) and asymmetric (224) planes by high resolution X-ray diffraction. The lateral correlation length and the mosaic spread are extracted for the epi-layer peaks in the asymmetric (224) diffraction. The most suitable annealing temperature to improve both the GeSn lattice quality and relaxation rate is about 500°C.

Novel group IV nano- and micro-structures for light sources on silicon

We present our recent researches on novel group IV nano- and micro-structures for potential light sources on Si, including the tensile strained Ge quantum dots (QDs), GeSn thin films and microstructures, and Ge(Sn) nanowires. Tensile-strained Ge QDs were grown by SS-MBE, and photoluminescence was achieved. The GeSn thin films were demonstrated with Sn concentration above the bandgap transition critical point, and partially suspended GeSn microstructures were fabricated for relaxing the compressive strain.

Suspended GeSn microstructure for light source on Si

A novel suspended GeSn microstructure is demonstrated by selective etching of GeSn thin film on Ge. XRD and μ-Raman measurements show that the compressive strain in the GeSn thin film is effectively relaxed, and furthermore, unexpected tensile strain was introduced in the suspended GeSn.

Spin Texture And Spin Injection In A 3D Topological Insulator

View Online Nano-Micro Conf., 2017, 1, 01063 | 1 Published by Nature Research Society http://nrs.org Spin Texture And Spin Injection In A 3D Topological Insulator W. M. Chen,* Y. Q. Huang, I. A. Buyanova, Y. X. Song, S. M. Wang Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden State Key Laboratory of Functional Materials for Informatics, CAS Center of Excellence for Superconducting Electronics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, China Corresponding Author. Email: wmc@ifm.liu.se Received: 31 May 2017, Accepted: 12 June 2017, Published Online: 30 October 2017 Citation Information: W. M. Chen, Y. Q. Huang, I. A. Buyanova, Y. X. Song, S. M. Wang, Nano-Micro Conference, 2017, 1, 01063 doi: 10.11605/ cp.nmc2017.01063

Origin of a fourfold symmetric (0 0 0 6) Bragg diffraction intensity in φ-scan mode on a 6H-SiC crystal

The quality of silicon carbide (SiC), when used as a substrate, has profound effects on the growth of the homo/hetero-epitaxial film on it. Here, a fourfold symmetric (0006) x-ray diffraction intensity in a -scan mode is found to have nothing to do with the deformation of wafers or the existence of mosaic domains, regardless of whether it is a double-sided polished 6H-SiC wafer or a thick 6H-SiC slice. The experimental results show that both the diffraction intensity and its full width at half maximum as a function of the azimuth angle exhibit the features of four peaks and four valleys regularly. By measuring the bending of the diffraction planes along the azimuth angles at the peaks and valleys, saddle-shaped deformed (0 0 0 1) atomic planes of the 6H-SiC in macroscopic scale are hypothesized. Based on the hypothesis, a model analysis of the diffraction intensity matched well with the observed anisotropic symmetric x-ray diffraction in a 6H-SiC single crystal.