Bingqian Song

Origin of colossal dielectric permittivity of rutile Ti0.9In0.05Nb0.05O2: single crystal and polycrystalline

In this paper, we investigated the dielectric properties of (In + Nb) co-doped rutile TiO2 single crystal and polycrystalline ceramics. Both of them showed colossal, up to 104, dielectric permittivity at room temperature. The single crystal sample showed one dielectric relaxation process with a large dielectric loss. The voltage-dependence of dielectric permittivity and the impedance spectrum suggest that the high dielectric permittivity of single crystal originated from the surface barrier layer capacitor (SBLC). The impedance spectroscopy at different temperature confirmed that the (In + Nb) co-doped rutile TiO2 polycrystalline ceramic had semiconductor grains and insulating grain boundaries, and that the activation energies were calculated to be 0.052 eV and 0.35 eV for grain and grain boundary, respectively. The dielectric behavior and impedance spectrum of the polycrystalline ceramic sample indicated that the internal barrier layer capacitor (IBLC) mode made a major contribution to the high ceramic dielectric permittivity, instead of the electron-pinned defect-dipoles.

Large lateral photovoltaic effect with ultrafast relaxation time in SnSe/Si junction

In this paper, we report a large lateral photovoltaic effect (LPE) with ultrafast relaxation time in SnSe/p-Si junctions. The LPE shows a linear dependence on the position of the laser spot, and the position sensitivity is as high as 250 mV mm−1. The optical response time and the relaxation time of the LPE are about 100 ns and 2 μs, respectively. The current-voltage curve on the surface of the SnSe film indicates the formation of an inversion layer at the SnSe/p-Si interface. Our results clearly suggest that most of the excited-electrons diffuse laterally in the inversion layer at the SnSe/p-Si interface, which results in a large LPE with ultrafast relaxation time. The high positional sensitivity and ultrafast relaxation time of the LPE make the SnSe/p-Si junction a promising candidate for a wide range of optoelectronic applications.

Fast and sensitive lateral photovoltaic effects in Fe3O4/Si Schottky junction

In this paper, we report the fast and sensitive lateral photovoltaic (LPE) effects in a Fe3O4/Si junction. Good rectifying I–V characteristics and large LPE are observed in the Fe3O4/Si junction. The LPE exhibits a linear dependence on the position of the laser spot, and the position sensitivity can reach 32.5 mV mm−1. The optical response time and relaxation time of LPE were ∼60 ns and 5 μs, respectively. The enhanced LPE properties and the fast relaxation time in the Fe3O4/Si junction were caused by the formation of the inversion layer in the interface of Fe3O4/Si.

Near-ultraviolet lateral photovoltaic effect in Fe 3 O 4 /3C-SiC Schottky junctions.

In this paper, we report a sensitive lateral photovoltaic effect (LPE) in Fe3O4/3C-SiC Schottky junctions with a fast relaxation time at near-ultraviolet wavelengths. The rectifying behavior suggests that the large build-in electric field was formed in the Schottky junctions. This device has excellent position sensitivity as high as 67.8 mV mm-1 illuminated by a 405 nm laser. The optical relaxation time of the LPE is about 30 μs. The fast relaxation and high positional sensitivity of the LPE make the Fe3O4/3C-SiC junction a promising candidate for a wide range of ultraviolet/near-ultraviolet optoelectronic applications.

Origin of the Ultrafast Response of the Lateral Photovoltaic Effect in Amorphous MoS2/Si Junctions

The lateral photovoltaic (LPV) effect has attracted much attention for a long time because of its application in position-sensitive detectors (PSD). Here, we report the ultrafast response of the LPV in amorphous MoS2/Si (a-MoS2/Si) junctions prepared by the pulsed laser deposition (PLD) technique. Different orientations of the built-in field and the breakover voltages are observed for a-MoS2 films deposited on p- and n-type Si wafers, resulting in the induction of positive and negative voltages in the a-MoS2/n-Si and a-MoS2/p-Si junctions upon laser illumination, respectively. The dependence of the LPV on the position of the illumination shows very high sensitivity (183 mV mm-1) and good linearity. The optical relaxation time of LPV with a positive voltage was about 5.8 μs in a-MoS2/n-Si junction, whereas the optical relaxation time of LPV with a negative voltage was about 2.1 μs in a-MoS2/p-Si junction. Our results clearly suggested that the inversion layer at the a-MoS2/Si interface made a good contribution to the ultrafast response of the LPV in a-MoS2/Si junctions. The large positional sensitivity and ultrafast relaxation of LPV may promise the a-MoS2/Si junctions applications in fast position-sensitive detectors.

Surface-migration driving uniform amorphous shell on crystalline nanowire: the case of SiC/SiOx core–shell nanowires

Single-crystal SiC nanowires with controlled surface amorphous silicon oxide (SiOx) layers, including bare SiC nanowires, chain-like and cable-like SiC/SiOx nanowires, have been synthesized by a catalyst-assisted chemical vapor reaction approach, and the temperature-dependent morphology evolution of the surface amorphous layers is investigated in detail. Morphological, compositional and structural characterizations indicate that as-synthesized SiC nanowires consist of cubic phase single crystal cores with [111] growth direction and amorphous SiOx shell with varied morphology that can be tuned by temperature. The growth of the SiC nanowires is governed by the vapor–liquid–solid mechanism while the variation of surface SiOx amorphous layers is thought to be controlled by a surface migration process that is mainly dependent on temperature. The results would be helpful to achieve rational modulation of amorphous surface layers on semiconductor nanowires.

Effect of a semiconductor electrode on the tunneling electroresistance in ferroelectric tunneling junction

We report the tunneling electroresistance effect (TER) in a Pt/BaTiO3(BTO)/Nb:SrTiO3 (n-STO) ferroelectric tunnel junction (FTJ). Using transmission electron microscopy, X-ray photoelectron spectroscopy, and piezoresponse force microscopy, we find that the thick BaTiO3 (5 nm) film is epitaxial and of high quality. A large ON/OFF resistance ratio of more than 104% at room temperature is observed. Our experimental results as well as theoretical modeling reveal that the depletion region near the BTO/n-STO interface can be electrically modulated via ferroelectric polarization, which plays a key role for the TER effect. Moreover, both long retention and high switching reproducibility are observed in the Pt/BTO/n-STO FTJ. Our results provide some fundamental understandings of the TER mechanism in the FTJs using a semiconductor electrode and will be useful for FTJ-based nonvolatile devices design.