Shuang Qiao

Magnetic and Gilbert damping properties of L21-Co2FeAl film grown by molecular beam epitaxy

Co2FeAl film with L21 structure was prepared. Its magnetic and Gilbert damping properties were studied by ferromagnetic resonance (FMR) and time-resolved magneto-optical Kerr effect (TR-MOKE), respectively. It is observed that the apparent damping parameter decreases drastically with increasing magnetic field at low field regime and eventually becomes a constant value of 0.004 at high field regime by TR-MOKE measurements. A Gilbert damping parameter of 0.008 in the hard axis by FMR measurement has also been obtained, which is comparable with that extracted from TR-MOKE measurements at low external field, indicating the extrinsic damping processes involved in the low field regime.

Growth temperature dependent structural and magnetic properties of epitaxial Co2FeAl Heusler alloy films

The structural and magnetic properties of a series of Co2FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co2FeAl films with an ordered L21 structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L21 structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

Large Lateral Photovoltage Observed in MoS2 Thickness-Modulated ITO/MoS2/p-Si Heterojunctions

Molybdenum disulfide (MoS2), as a typical two-dimensional (2D) material, has attracted extensive attention in recent years because of its fascinating optical and electric properties. However, the applications of MoS2 have been mainly in photovoltaic devices, field-effect transistors, photodetectors, and gas sensors. Here, it is demonstrated that MoS2 can be found another important application in position sensitive detector (PSD) based on lateral photovoltaic effect (LPE) in it. The ITO/MoS2(3, 5, 7, 9, 10, 20, 50, 100 nm)/p-Si heterojunctions were successfully prepared with vertically standing nanosheet structure of MoS2. Because of the special structure and the strong light absorption of the relatively thick MoS2 film, the ITO/MoS2/p-Si heterojunction exhibits an abnormal thickness-dependent LPE, which can be ascribed to the n- to p-type transformation of MoS2. Moreover, the LPE of ITO/MoS2/p-Si structure improves greatly because of forward enhanced built-in field by type transformation in a wide spectrum response ranging from visible to near-infrared, especially the noticeable improvement in infrared region, indicating its great potential application in infrared PSDs. This work not only suggest that the ITO/MoS2/p-Si heterojunction shows great potential in LPE-based sensors, but also unveils the importance of type transformation of MoS2 in MoS2-based photoelectric devices besides strong light absorption and suitable bandgap.

Temperature dependent magnetic anisotropy of epitaxial Co2FeAl films grown on GaAs

Co2FeAl films with different thickness were prepared at different temperature by molecular beam epitaxy. Their magnetic anisotropy was studied by rotating magneto-optical Kerr rotation measurements under different temperature. It is found that the cubic anisotropy depends only on the temperature-dependent fourth order magneto-elastic coefficients. However, the results of growth and measurement temperature-dependent uniaxial anisotropy suggest that the uniaxial anisotropy of Co2FeAl films may be attributed to contributions from both shear strain and anisotropic interfacial bonding. Our experimental findings proposed a new point of view to understand the origin of magnetic anisotropy in ferromagnet/GaAs(001) heterostructures.

Large lateral photovoltaic effect in a-Si:H/c-Si p–i–n structure with the aid of bias voltage

In this paper, for the first time, we report a significant enhancement of the lateral photovoltaic effect (LPE) in a hydrogenated amorphous silicon/monocrystalline Si (a-Si:H/c-Si) p–i–n structure via the application of a transverse bias voltage. The position sensitivity of this a-Si:H/c-Si p–i–n structure increased linearly with both laser power and wavelength, and the position sensitivity reached a minimum of 809 mV/mm for a 980 nm laser, which was approximately 43 times larger than that without the bias voltage. Moreover, this structure exhibited good linearity with nonlinearity of no more than 3%. We attribute this greatly improved LPE to the enhanced Schottky-barrier-dependent transmitted possibility of photo-generated holes.

The thickness-dependent dynamic magnetic property of Co2FeAl films grown by molecular beam epitaxy

Co2FeAl films with different thickness were prepared at different temperature by molecular beam epitaxy. Their dynamic magnetic property was studied by the time-resolved magneto-optical Kerr effect measurements. It is observed that the intrinsic damping factor of Co2FeAl for [100] orientation is not related to the films thickness and magnetic anisotropy as well as temperature at high-field regime, but increases with structural disorder of Co2FeAl. The dominant contribution from the inhomogeneous magnetic anisotropy is revealed to be responsible for the observed extremely nonlinear and drastic field-dependent damping factors at low-field regime.

Magnetic field-modulated photo-thermo-electric effect in Fe/GaAs film

Ferromagnet/semiconductor heterostructure, such as Fe/GaAs, is always one of the key issues in spintronics due to its prerequisite for the realization of spin sensitive devices. In this letter, a lateral photoelectric effect (LPE) was observed in Fe/GaAs. Our results show that the sensitivity was not related to laser wavelength, but only proportional to laser power, suggesting that the lateral photovoltage was induced by photo-thermo-electric effect. Moreover, we also observe that the voltage signal increases with the increase in applied field due to decreasing scattering probability for spin-polarized electrons. Our finding of LPE adds another functionality to the Fe/GaAs system and will be useful in development of spin-polarized voltage devices.

Ultrahigh, Ultrafast, and Self-Powered Visible-Near-Infrared Optical Position-Sensitive Detector Based on a CVD-Prepared Vertically Standing Few-Layer MoS2/Si Heterojunction

Abstract MoS2, as a typical transition metal dichalcogenide, has attracted great interest because of its distinctive electronic, optical, and catalytic properties. However, its advantages of strong light absorption and fast intralayer mobility cannot be well developed in the usual reported monolayer/few‐layer structures, which make the performances of MoS2‐based devices undesirable. Here, large‐area, high‐quality, and vertically oriented few‐layer MoS2 (V‐MoS2) nanosheets are prepared by chemical vapor deposition and successfully transferred onto an Si substrate to form the V‐MoS2/Si heterojunction. Because of the strong light absorption and the fast carrier transport speed of the V‐MoS2 nanosheets, as well as the strong built‐in electric field at the interface of V‐MoS2 and Si, lateral photovoltaic effect (LPE) measurements suggest that the V‐MoS2/Si heterojunction is a self‐powered, high‐performance position sensitive detector (PSD). The PSD demonstrates ultrahigh position sensitivity over a wide spectrum, ranging from 350 to 1100 nm, with position sensitivity up to 401.1 mV mm−1, and shows an ultrafast response speed of 16 ns with excellent stability and reproducibility. Moreover, considering the special carrier transport process in LPE, for the first time, the intralayer and the interlayer transport times in V‐MoS2 are obtained experimentally as 5 and 11 ns, respectively.

The Reverse Lateral Photovoltaic Effect in Boron-Diffused Si p-n Junction Structure

Lateral photovoltaic effect (LPE) in boron-diffused Si p-n junction has been first studied by using different laser sources with wavelength ranging from visible to infrared. Our results suggest that the LPEs of both sides increased with laser wavelength and the lateral photovoltage (LPV) exhibited the reverse polarity for p-Si side and n-Si side of the junction. Moreover, the LPV on n-Si side was slightly larger than that on p-Si side when illuminating on the indium-tin oxide side, and the LPVs on p-Si side and n-Si side for illuminating on the p-Si side were accordingly larger than that for illuminating on the n-Si side. Based on the different mobilities of carriers, the recombination of surface defects, and the wavelength-dependent quantum efficiency, these results are well explained.

Large lateral photovoltaic effect in µc-SiOx:H/a-Si:H/c-Si p–i–n structure

In this paper, we report on a large lateral photovoltaic effect (LPE) in a hydrogenated microcrystal silicon-oxygen (µc-SiOx:H)-based p–i–n structure. Compared with LPE in a hydrogenated amorphous silicon (a-Si:H)-based p–i–n structure, this structure showed an abnormal current–voltage (I–V) curve with a lower photoelectric conversion efficiency, but exhibited a much higher LPE with the highest position sensitivity of 64.3 mV/mm. We ascribe this to the enhancement of the lateral gradient of excess transmitted carriers induced by increasing both Schottky barrier and p-type layer body conductivity. Our results suggest that this µc-SiOx:H-based p–i–n structure may be a promising candidate for position-sensitive detectors (PSDs). Moreover, our results may also imply that solar cell devices with abnormal I–V curves (or low efficiency) could find their new applications in other aspects.