Tie Lin

Ultrasensitive and Broadband MoS2 Photodetector Driven by Ferroelectrics

A few-layer MoS2 photodetector driven by poly(vinylidene fluoride-trifluoroethylene) ferroelectrics is achieved. The detectivity and responsitivity are up to 2.2 × 10(12) Jones and 2570 A W(-1), respectively, at 635 nm with ZERO gate bias. E(g) of MoS2 is tuned by the ultrahigh electrostatic field from the ferroelectric polarization. The photoresponse wavelengths of the photodetector are extended into the near-infrared (0.85-1.55 μm).

Dielectric responses and scaling behaviors in Aurivillius Bi6Ti3Fe2O18 multiferroic thin films

Dielectric responses and scaling behaviors of Aurivillius Bi6Ti3Fe2O18 (BTF2) multiferroic thin films were systemically detailed by the temperature-dependent dielectric/impedance spectroscopy. We clarified two dielectric relaxation processes presented in grain interior of the BTF2 films. One relaxation below ∼500 K was proposed to associate with the localized hopping process of carrier between Fe3+ and Fe2+ inside the grains. Another one above ∼500 K arose from the long-range movement of oxygen vacancies. The scaling behaviors implied that the distribution of relaxation times for oxygen vacancies was temperature independent while the dynamical processes for the hopping carriers presumably depended on temperature.

Electrical, magnetic, and optical properties in multiferroic Bi5Ti3FeO15 thin films prepared by a chemical solution deposition route

Perovskite Aurivillius structure Bi5Ti3FeO15 (BTF) polycrystalline thin films were prepared by a chemical solution deposition route. The microstructure, electrical, and magnetic properties were investigated and in particular the optical properties of the BTF films were addressed. The coexistence of the ferroelectric and weak ferromagnetic properties at room temperature demonstrates the multiferroic behavior of the BTF films. The optical dielectric functions in the photon energy range of 1.13–4.13 eV have been extracted by fitting the experimental data in terms of the Tauc-Lorentz and Cauchy models. A direct interband transition is allowed and the energy bandgap is determined to be ∼3.3 eV for the BTF films. The weak absorption below the bandgap edge was observed and described by the Urbach band tail rule. Finally, the optical dispersion behaviors of the BTF films in the transparent region were explained using a single oscillator model.

Low-temperature preparation of highly (100)-oriented Pb(ZrxTi1−x)O3 thin film by high oxygen-pressure processing

A method for thin-film fabrication employing high oxygen-pressure processing (HOPP) was developed. With this method, the highly (100) oriented Pb(ZrxTi1−x)O3 (PZT) thin film was fabricated at temperature as low as 400°C. HOPP is compatible to the ferroelectric PZT film integration with a readout integrated circuit. The sol-gel-derived PZT 50∕50 thin film showed a well-saturated hysteresis loop at an applied electric field of 367kV∕cm with Pr and Ec of 45μC∕cm2 and 121kV∕cm, respectively. Large electric leakage was attributed to remnant organic components, which was demonstrated by sputtered organic-free PZT films. The optimized Pr and Ec are of 26μC∕cm2 and 93kV∕cm under an applied electric field of 400kV∕cm.

Hopping conduction and low-frequency dielectric relaxation in 5mol% Mn doped (Pb,Sr)TiO3 films

The highly (00l)-oriented 5 mol % Mn doped Pb0.5Sr0.5TiO3 films with remarkable ferroelectric properties (2Pr=27.1 μC/cm2 and 2Ec=55.5 kV/cm) were fabricated on LaNiO3 coated silicon substrates by chemical solution deposition. The ac conductivity and the dielectric response of the films at various temperatures were studied. Hopping conduction accompanied by the dielectric relaxation at low frequencies was observed. The results can be correlated with the thermal-activated short range hopping of localized charge carriers through trap sites separated by potential barriers with different heights, i.e., localized electrons hopping between multivalence Mn sites (the activation energy of this hopping process is ∼0.4 eV), which is also established in terms of the correlated barrier hopping model.

Temperature dependence of ferroelectric and dielectric properties of PbZr0.5Ti0.5O3 thin film based capacitors

The temperature dependence of the ferroelectric and dielectric properties of PbZr0.5Ti0.5O3 thin films deposited on LaNiO3-coated SrTiO3 substrate was investigated. The results showed that both the saturation polarization and remanent polarization increased with decreasing temperature from 300 to ∼50 K, and decreased as the temperature continued to decrease below 40 K. The capacitance of the PbZr0.5Ti0.5O3 ferroelectric thin film capacitor as a function of small ac field and temperature was measured, and the data were processed using Rayleigh law. It was demonstrated that both the reversible and irreversible contributions to the dielectric constant decreased with decreasing temperature; however, they showed an increase when the temperature dropped below 50 K. The anomalous behavior of the temperature dependence may be attributed to a phase transition in the PbZr0.5Ti0.5O3 thin film in the vicinity of 50 K.

Highly sensitive phototransistor based on GaSe nanosheets

Phototransistors based on two dimensional semiconductors have drawn increasing attention in recent years. GaSe is a typical semiconductor with a layered structure. In this work, the ultrathin GaSe nanosheets were exfoliated from commercially available crystals using a micromechanical cleavage technique. Then, the nanosheets were used to fabricate field effect transistors (FETs) on Si/SiO2 substrates with interdigitated electrodes. The electrical and optoelectronic properties of the FET were characterized. The phototransistor based on a GaSe nanosheet had a high photoresponsivity (∼2200 mA/W) and a high Iphoto/Idark (photoresponse current over dark current) ratio of almost 103.

Electrical and optical properties of Bi2Ti2O7 thin films prepared by metalorganic decomposition method

Highly (111) oriented Bi2Ti2O7 thin films have been grown on Pt∕Ti∕SiO2∕Si and Al2O3 substrates by metalorganic decomposition method at 550°C. The structural properties of the films were examined by x-ray diffraction. The Bi2Ti2O7 films exhibit good insulating property and the leakage current density of the film on Pt∕Ti∕SiO2∕Si is only about 1.56×10−8A∕cm2 at 200kV∕cm. The refractive index and extinction coefficient of Bi2Ti2O7 thin films were determined by fitting the infrared spectroscopic ellipsometric data using a classical dielectric function formula. As the wavelength increases, the refractive index decreases, while the extinction coefficient increases. And the band-gap energy Eg was obtained from the optical transmission spectra of Bi2Ti2O7 thin films.

The Cr-substitution concentration dependence of the structural, electric and magnetic behaviors for Aurivillius Bi5Ti3FeO15 multiferroic ceramics

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Cr-doped concentrations have been synthesized by the conventional solid state reaction method. The influences of Cr-doping concentrations on the structural, magnetic, dielectric, and ferroelectric properties of BTFO ceramics are investigated in detail. All these sintered Cr-substituted BTFO ceramics are determined to be layered perovskite Aurivillius structure by X-ray diffraction, as well as the lattice parameters a, b, and c are in good accordance with Vegards law along with the Cr-doping concentration. The lattice distortion a/b for Aurivillius family decreases with increasing Cr-doping concentration. Moreover, Cr-doping can promote greatly the grain growth of BTFO samples confirmed from field emission scanning electron microscopy characterization. However, no obvious signs of the improvement in ferroelectric properties are found in Cr-doped BTFO ceramics, and abnormal ferroelectric polarization versus electric field (P-E) loops are o...

Visible to short wavelength infrared In2Se3-nanoflake photodetector gated by a ferroelectric polymer

Photodetectors based on two-dimensional (2D) transition-metal dichalcogenides have been studied extensively in recent years. However, the detective spectral ranges, dark current and response time are still unsatisfactory, even under high gate and source-drain bias. In this work, the photodetectors of In2Se3 have been fabricated on a ferroelectric field effect transistor structure. Based on this structure, high performance photodetectors have been achieved with a broad photoresponse spectrum (visible to 1550 nm) and quick response (200 μs). Most importantly, with the intrinsic huge electric field derived from the polarization of ferroelectric polymer (P(VDF-TrFE)) gating, a low dark current of the photodetector can be achieved without additional gate bias. These studies present a crucial step for further practical applications for 2D semiconductors.