Shuhong Hu

Self-Induced Uniaxial Strain in MoS2 Monolayers with Local van der Waals-Stacked Interlayer Interactions

Strain engineering is an effective method to tune the properties of electrons and phonons in semiconductor materials, including two-dimensional (2D) layered materials (e.g., MoS2 or graphene). External artificial stress (ExAS) or heterostructure stacking is generally required to induce strains for modulating semiconductor bandgaps and optoelectronic functions. For layered materials, the van der Waals-stacked interlayer interaction (vdW-SI) has been considered to dominate the interlayer stacking and intralayer bonding. Here, we demonstrate self-induced uniaxial strain in the MoS2 monolayer without the assistance of ExAS or heterostructure stacking processes. The uniaxial strain occurring in local monolayer regions is manifested by the Raman split of the in-plane vibration modes E2g(1) and is essentially caused by local vdW-SI within the single layer MoS2 due to a unique symmetric bilayer stacking. The local stacked configuration and the self-induced uniaxial strain may provide improved understanding of the fundamental interlayer interactions and alternative routes for strain engineering of layered structures.

Growth and Raman spectra of GaSb quantum dots in GaAs matrices by liquid phase epitaxy

The self-assembled type-II GaSb quantum dots (QDs) are successfully grown on semi-insulting GaAs (100) matrix by liquid phase epitaxy technique. The topography of QDs with high growth temperature is characterized by atomic force microscopy (AFM). The cap layer, which is needed for the device fabrication, is obtained for only some tens of nanometers. The non-resonant Raman spectra are applied to investigate the GaSb-like optical phonons localized in the QDs and to confirm convincingly the existence of GaSb QDs.

Two methods for characterizing the electrical properties of InAsSb film grown by liquid phase epitaxy

High-quality InAs1-xSbx films with x=0.06 have been successfully grown on InAs (100) substrates by liquid phase epitaxy. Two methods are used to characterize the electrical properties of InAsSb film. One is to grow InAsSb epilayer on p-type InAs substrate, which, in combination with the n-type epilayer, forms a p-n junction to prevent the parallel conduction from the substrate. The other is that both the conductive InAs substrate and the dislocation layer between InAs and InAsSb are removed completely by chemical mechanical polishing method to get InAsSb film glued onto insulating sapphire substrate. The influence of conductive InAs substrate on the electrical properties of InAsSb film is eliminated effectively.

Internal polyhedron configuration energy self-sufficient system for sphere mobile platform

Under the requirements of flexible, stealthy and miniaturize, the energy system has become the most critical factor that constraint the performance of smart unmanned equipment. Due to its advantages of convenient movement and strong environmental adaptability, the sphere platform shows broad prospects in military and civilian application. This paper designed an energy self-sufficient sphere platform equipped with intelligence reconnaissance device. The energy module of the device consists of an inscribed polyhedron solar cell array. The high power density energy storage component inside the sphere realizes energy storage and power supply for the signal transmission module. The sphere is equipped with an autonomous mobile unit and a detection unit, activated by outside trigger signal, and can be used in close reconnaissance, short-range detection and strategic destruction. The output power of the prototype machine produced by 3D printing is close to the theoretical result, and it maintained in high value during device rotation, laying the technical foundation for the practical application of this spherical platform.

Surface morphology of LPE-growth GaSb quantum dots

The self-assembled type-II GaSb quantum dots (QDs) were successfully grown on semi-insulting GaAs (100) substrate by the liquid phase epitaxy (LPE) technique with growth temperature ranging from 520 to 580 oC. The morphology of GaSb QDs including size, shape and density was investigated by atomic force microscopy measurement and scanning electron microscope measurement, respectively. The cap layer with scores of nanometers, which is characterized by Profile-system, is obtained for the photoluminescence measurement and device fabrication.

Single crystalline InAsxSb1-x grown on (100) InSb substrate by liquid phase epitaxy

Single crystalline InAs0.016Sb0.984 film has been successfully grown on (100) InSb substrate by LPE method. A large supercooling (ΔT = 15 °C) had been used to prevent substrate from dissolving into the epilayer. High resolution X-ray diffraction (HRXRD) measurement was used to characterize the crystal quality of the film. Only (200) and (400) peaks were observed from the XRD spectrum, indicating that the film was single crystalline with (100) orientation. The Fourier transform infrared (FTIR) transmission spectrum of the film at room temperature revealed 7.77 μm cut-off wavelength of the film. The lattice dynamics of the epilayer was studied by Raman scattering, suggests two-mode behavior of the optical phonons.

High quality mid-infrared InAs film grown on (100) GaSb substrate by LPE using a ternary melt

InAs film has been successfully grown on (100) GaSb substrate using a ternary In-As-Sb melt by liquid phase epitaxy (LPE). The high resolution X-ray diffraction (HRXRD) and Rocking curve showed the film was single crystalline InAs with high quality. The Fourier transform infrared (FTIR) transmission spectrum revealed that the cutoff wavelength was about 3.8 μm at room temperature. The electron mobility at 300 K is higher than 2×10 4cm2/Vs. It indicates that the structure of InAs/GaSb prepared by LPE has a potential for mid-infrared devices.

Effects of annealing on InAsSb films grown by the modified LPE technique

We have studied the annealing effects on InAsSb thick films grown by the modified liquid phase epitaxy (LPE) technique. Appropriate annealing treatment can efficiently eliminate Sb vacancy and stain which are formed during growing process, thus it is necessary to study the influence of annealing condition (temperature, ambient, time and cooling rate) on the properties of InAsSb epilayer. The X-ray diffraction measurement (XRD) showed the annealed InAsSb films were polycrystalline with (111)-preferred orientation, except for the two samples annealed with 350 °C for 15 hours and with rapid cooling rate, respectively, which exhibited a (100)-preferred orientation. The Fourier transform infrared (FTIR) revealed a cut off wavelength more than 10 μm for the samples. Also, the infrared transmittance would be improved due to decreasing of film defects by appropriate annealing treatment. Measurement of electrical properties for samples revealed the increase of electron mobility and the reduce of carrier concentration at 77K when keeping anneal temperature low at 350 °C and extending anneal time, indicating the electrical improvement of the InAsSb layers.