Leakage mechanism in AlxGa1-xN/GaN heterostructures with AlN interlayer

Leakage of AlxGa1-xN/GaN heterostructures was investigated by admittance–voltage profiling. Nominally undoped structures were grown by low-pressure metal-organic vapor-phase epitaxy (MOVPE). The investigated structures had an Al-content of 30 %. They are compared to structures with an additional 1 nm thick AlN interlayer placed before the Al0.3Ga0.7N layer growth, originally to improve device performance. Conductance of FET devices with AlN interlayer, measured from depletion of the two-dimensional electron gas (2DEG) to zero volt bias at frequencies ranging from 50 Hz to 10 kHz, could be described by free charge carriers using a Drude model. The voltage dependent conductance shows a behavior described by either Poole-Frenkel emission or Schottky emission. From the size of the conductance, as well as simulation of the tunneling current injected from the gate under off-state conditions by universal Schottky tunnelling, Schottky Emission is obvious. Evaluating the data by Schottky emission, we can locate the leakage path, of tens of nm in the range between gate and drain/source with contact to the 2DEG, originating from the AlN interlayer. The static dielectric constant in growth direction, necessary for the evaluation, is determined from various AlxGa1 xN/GaN heterostructures to ε||(0) = 10.7 +/- 0.1.

Numerical calculation of transient electric field considering space charge in oil-paper insulation of converter transformers

Purpose The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation. Design/methodology/approach The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field. Findings A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified. Originality/value A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

Transfer phenomenon of charge carriers in crystals of Ca(Al0.1Ga0.9)2S4:Eu2+

Research study of volt-amperage properties (VAP) of [Formula: see text] crystals determined the mechanism of current flow though the studied samples and this mechanism is based on barrier Schottky emission and emission of Franklin–Paul. The dielectric constant of the material, height of the potential barrier on metal–semiconductor border, concentration of the traps and the effective mass of electrons are calculated.

ELECTRICAL CHARACTERIZATION OF METAL JUNCTION FORMED WITH PURE AND POLYANILINE-BLENDED POLY(SCHIFF BASE) POLYMER

In this paper, we demonstrate the formation of Schottky contact formed by Al with a new class of synthesized conjugated pure poly(Schiff base) (PSB) and its blend with varied concentrations of polyaniline (PANI). The Schottky behavior was transformed into Ohmic in the blended polymer. PSB was synthesized from the solution of polycondensation of terephthaloyl chloride (T) and 4-(4-hydroxybenzylideneamino)phenol (SB). The polymer showed good thermal stability with [Formula: see text] of 312∘C as determined by thermal gravimetric analysis–differential scanning calorimetry TGA–DSC and high molecular weight [Formula: see text] (g/mol) with coiled conformation as determined by laser light scattering. PBS was blended with various weight percentage ratios of PANI (0, 3, 6, 9, 12, 15 percent by weight of the pristine polymer). The metal contact (Au) was formed and studied in the temperature range of 293–373[Formula: see text]K, which showed that Schottky behavior in the intrinsic polymer with an ideality factor was close to 2 and then reduced to 1.0–1.2 in the blended polymers. In blended polymers, the conduction across the junction was characterized by Schottky emission at low field and Poole–Frenkel emission at high field. The Schottky barrier height showed a small increase with temperature, which was attributed to reduction in the built up of image charge. The Schottky and Poole–Frenkel emission coefficients were also determined and Schottky emission coefficient agreed with the theoretical value, while Poole–Frenkel emission coefficient was small. In short, the metal–semiconductor junction was affected by the blending, while conduction within the polymer remained independent of PANI concentration.

Leakage Current Conduction Mechanism of Au-Pt-Ti/ HfO2-Al2O3/n-InAlAs Metal-Oxide-Semiconductor Capacitor under Reverse-Biased Condition

Au-Pt-Ti/high-k/n-InAlAs metal-oxide-semiconductor (MOS) capacitors with HfO2-Al2O3 laminated dielectric were fabricated. We found that a Schottky emission leakage mechanism dominates the low bias conditions and Fowler–Nordheim tunneling became the main leakage mechanism at high fields with reverse biased condition. The sample with HfO2 (4 m)/Al2O3 (8 nm) laminated dielectric shows a high barrier height ϕB of 1.66 eV at 30 °C which was extracted from the Schottky emission mechanism, and this can be explained by fewer In–O and As–O states on the interface, as detected by the X-ray photoelectron spectroscopy test. These effects result in HfO2 (4 m)/Al2O3 (8 nm)/n-InAlAs MOS-capacitors presenting a low leakage current density of below 1.8 × 10−7 A/cm2 from −3 to 0 V at 30 °C. It is demonstrated that the HfO2/Al2O3 laminated dielectric with a thicker Al2O3 film of 8 nm is an optimized design to be the high-k dielectric used in Au-Pt-Ti/HfO2-Al2O3/InAlAs MOS capacitor applications.