Ligang Gao

Effective dielectric constant of a two-component material with shape distribution

The effective dielectric constant of a two-component material is investigated. By considering the shape distribution of the components, we derive Maxwell-Garnett-type approximation, which has been established based on the reciprocity theorem (del Rio J A et al 1998 Solid State Commun. 106 183). Based on a self-consistent condition on the electric field (Bruggeman-type effective medium approximation), we obtain the well-known Lichteneckers mixture formulae with α = 1/2. Moreover, we derive the differential effective medium approximation by taking into account the shape distribution. All these formulae are checked through the spectral density function and compared with previous bounds.

Electrical field induced precipitation reaction and percolation in Ag30Ge17Se53 amorphous electrolyte films

The microstructural evolution and resistive switching of glassy Ag30Ge17Se53 electrolyte films clipped by Ag active electrode, at which a positive bias was applied, and Pt inert electrode, were investigated by transmission electron microscopy observations and I-V measurements as functions of the period of electrical field treatment. It is revealed that an electrical field induced precipitation reaction forming conductive particles with orthorhombic Ag2Se structure and followed growth and networking of these particles, leading to an electrical percolation, are responsible for the transition from high resistive to high conductive state of the system. The kinetics of the precipitation reaction was also analyzed.

The growth of metallic nanofilaments in resistive switching memory devices based on solid electrolytes

Memory cells with sandwich structure based on solid electrolytes Ag30S2P14O42, called ASP, were fabricated on Pt/Ti/Si(001) wafers by using pulsed laser deposition and focused ion beam nanofabrication technique. The current-voltage characteristic of the ASP memory units shows satisfactory switching behaviors. The switching of the devices was explained by the formation and rupture of Ag nanofilaments with the help of bipolar electrical pulses. A simplified model was proposed to describe the growth of the Ag nanofilaments. It was shown that the effective cross section area of the Ag nanofilaments increased at initial stage, then decreased after reaching a maximum until the top and bottom electrodes were connected.

The thermal stability and electrical properties of LaErO3 films as high-k gate dielectrics

Lanthanum erbium oxide thin films have been deposited on an Si (1 0 0) wafer by using the pulsed laser deposition technique. The thermal and electrical properties of LaErO3 films were investigated by x-ray diffraction, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Capacitance measurements reveal good C–V curves with an equivalent oxide thickness of 1.4 nm and little hysteresis. Transmission electron microscopic images reveal that the 6.5 nm LaErO3 film shows a thin interfacial layer even after being annealed in N2 at 700 °C for 30 s. X-ray photoelectron spectroscopic spectra indicate that little SiO2 was formed at the interface during the deposition of LaErO3 films. The measured thermal and electrical properties of the thin film suggest that the LaErO3 film should be a promising candidate for future high-k gate dielectrics.

Band alignments and improved leakage properties of (La2O3)0.5(SiO2)0.5/SiO2/GaN stacks for high-temperature metal-oxide-semiconductor field-effect transistor applications

The band alignments of (La2O3)0.5(SiO2)0.5(LSO)/GaN and LSO/SiO2/GaN gate dielectric stacks were investigated comparatively by using x-ray photoelectron spectroscopy. The valence band offsets for LSO/GaN stack and LSO/SiO2/GaN stack are 0.88 and 1.69 eV, respectively, while the corresponding conduction band offsets are found to be 1.40 and 1.83 eV, respectively. Measurements of the leakage current density as function of temperature revealed that the LSO/SiO2/GaN stack has much lower leakage current density than that of the LSO/GaN stack, especially at high temperature. It is concluded that the presence of a SiO2 buffer layer increases band offsets and reduces the leakage current density effectively.

Effect of NH3 and N2 annealing on the interfacial and electrical characteristics of La2O3 films grown on fully depleted SiGe-on-insulator substrates

The interfacial structure and the electrical properties of pulsed laser deposition derived La2O3 ultra-thin films on fully depleted SiGe-on-insulator (FD SGOI) substrates before and after post-annealing in NH3 and N2, respectively, have been investigated comparatively. The results from high-resolution transmission electron microscopy and x-ray photoelectron spectroscopic revealed that interface reactions take place after the NH3 and N2 annealing process, but, as compared with the N2 annealing process, the NH3 annealing process can effectively decrease the thickness of the interfacial layer and incorporate more nitrogen at the dielectric/SiGe interface, resulting in smaller equivalent oxide thickness. The La2O3 capacitors annealed in NH3 show good capacitance–voltage characteristics with negligible hysteresis, smaller interface trap density and lower gate-leakage current density in comparison with those of capacitors annealed in N2. It is demonstrated that the NH3 annealing process can be a promising technology in improving the quality of high-k dielectric on FD SGOI substrates.

Monte Carlo simulation of the percolation in Ag30Ge17Se53 amorphous electrolyte films

Monte Carlo simulations using a dielectrophoresis model were performed to investigate the microstructural evolution and the conductance change of an Ag30Ge17Se53 electrolyte film clapped by a Ag active electrode, at which a positive bias was applied, and a Pt inert electrode. It has been revealed that driven by the electrical field Ag ions were injected into the electrolyte from the Ag electrode to form conductive particles, thereafter, the particles align themselves in nanowires connecting Ag electrode and Pt electrode and leading to an electrical percolation. It is responsible for the resistive switching of the system. The transmission electron microscopic observations and resistive measurement results are in good agreement with the results of simulations.

Characterization of Titania Incorporated with Alumina Nanocrystals and Their Impacts on Electrical Hysteresis and Photoluminescence

The structural and optical characterizations of titania incorporated with alumina nanocrystals have been presented in this paper and the films exhibit excellent properties like low current density, small hysteresis as well as high photoluminescence quantum yields of about 361 nm. These properties are promising for the applications in future electronic devices.

Modulation of the band offsets between La2Hf2O7 and fully depleted SiGe on insulator by NH3 treatment

Band alignments of La2Hf2O7 (LHO) films grown on fully depleted SiGe on insulator (FD SGOI) substrates have been investigated by x-ray photoelectron technique. The valence and conduction band offsets for LHO/FD SGOI systems are determined to be 3.25 and 1.49 eV, respectively. Such asymmetric band alignment can be modulated to be quite symmetric by the surface nitridation of FD SGOI using NH3 treatment. The impact of NH3-treatment temperature on band offsets is also investigated.