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

2021 ◽  
Author(s):  
Klaus Köhler ◽  
Wilfried Pletschen ◽  
Lutz Kirste ◽  
Stefano Leone ◽  
Stefan Müller ◽  
...  
Keyword(s):  
Tunneling Current ◽  
Growth Direction ◽  
Layer Growth ◽  
Schottky Emission ◽  
Al Content ◽  
Leakage Mechanism ◽  
Voltage Dependent ◽  
Metal Organic ◽  
Frenkel Emission ◽  
Dimensional Electron Gas

Abstract 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.

scholarly journals Modeling the Layer-by-Layer Growth of HKUST-1 Metal-Organic Framework Thin Films

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1631
Author(s):  
Qiang Zhang ◽  
Yohanes Pramudya ◽  
Wolfgang Wenzel ◽  
Christof Wöll
Keyword(s):  
Thin Films ◽  
Surface Roughness ◽  
Deposition Rate ◽  
Layer Growth ◽  
Coarse Grained ◽  
Structural Defects ◽  
Effect Of Temperature ◽  
Layer By Layer ◽  
Reactant Concentration ◽  
Metal Organic

Metal organic frameworks have emerged as an important new class of materials with many applications, such as sensing, gas separation, drug delivery. In many cases, their performance is limited by structural defects, including vacancies and domain boundaries. In the case of MOF thin films, surface roughness can also have a pronounced influence on MOF-based device properties. Presently, there is little systematic knowledge about optimal growth conditions with regard to optimal morphologies for specific applications. In this work, we simulate the layer-by-layer (LbL) growth of the HKUST-1 MOF as a function of temperature and reactant concentration using a coarse-grained model that permits detailed insights into the growth mechanism. This model helps to understand the morphological features of HKUST-1 grown under different conditions and can be used to predict and optimize the temperature for the purpose of controlling the crystal quality and yield. It was found that reactant concentration affects the mass deposition rate, while its effect on the crystallinity of the generated HKUST-1 film is less pronounced. In addition, the effect of temperature on the surface roughness of the film can be divided into three regimes. Temperatures in the range from 10 to 129 °C allow better control of surface roughness and film thickness, while film growth in the range of 129 to 182 °C is characterized by a lower mass deposition rate per cycle and rougher surfaces. Finally, for T larger than 182 °C, the film grows slower, but in a smooth fashion. Furthermore, the potential effect of temperature on the crystallinity of LbL-grown HKUST-1 was quantified. To obtain high crystallinity, the operating temperature should preferably not exceed 57 °C, with an optimum around 28 °C, which agrees with experimental observations.

Metal-organic framework (MOF) composites for photodegradation of hazardous organic materials

2021 ◽  
Vol 02 ◽  
Author(s):  
Xinxin Liu ◽  
Jiaqing Ren ◽  
Jiaqi Fang ◽  
An Pan ◽  
Nianqiao Qin ◽  
...  
Keyword(s):  
Photocatalytic Degradation ◽  
Organic Pollutants ◽  
Metal Organic Framework ◽  
Stable Process ◽  
Layer Growth ◽  
Thermal Method ◽  
Layer By Layer ◽  
Wide Range ◽  
Metal Organic ◽  
Organic Framework

: Photocatalytic degradation is an energy-efficient, cost-effective, and stable process that has a wide-range of applications. It is considered a promising method for the removal of organic pollutants. As a new type of porous materials, Metal-organic framework (MOF) composites have been proven to be an ideal catalyst for the degradation of organic pollutants due to their small size and large specific surface area. In this review, several common preparation methods of MOF composites are evaluated：microwave synthesis, solvent-thermal method, electrochemical method and layer by layer growth method. The degradation effects of MOF composites on different organic pollutants are summarized, and the excellent photocatalytic performances of some MOF composites are demonstrated. Finally, the prospect of photocatalytic degradation of organic pollutants by MOF composites is examined, and the challenges of further development of MOF composites are discussed.

scholarly journals Recent Results in the Crystal Growth of GaN at High N2 Pressure

1996 ◽  
Vol 1 ◽  
Author(s):  
I. Grzegory ◽  
M. Bockowski ◽  
B. Lucznik ◽  
S. Krukowski ◽  
M. Wroblewski ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Growth Direction ◽  
Layer Growth ◽  
Seeded Growth ◽  
Bulk Crystal Growth ◽  
Bulk Gan ◽  
Experimental Solubility Data ◽  
Stable Growth ◽  
Image Position ◽  
Homoepitaxial Layers

We present recent results on bulk GaN crystallization. The best quality GaN crystals grown from the solution at high N2 pressure without an intentional seeding are single crystalline platelets of stable morphology reaching dimensions up to 10 mm. The fastest growth direction for such crystals is [1 0 0], perpendicular to the GaN c-axis. The maximum stable growth rate perpendicular to crystal c-axis is determined from the experiment and used for an estimate of the effective supersaturation for the {10 0} face assuming two dimensional layer growth. The heat of GaN disssolution, determined from experimental solubility data, is used for the estimation of the edge energy of 2-D nuclei on the growing {10 0} face. Bulk crystal growth seeded by a single hexagonal needle with well developed {10 0} faces is also reported. The crystallization mechanisms and morphological stability in seeded growth of GaN are discussed on the basis of experimental results. The physical properties of the GaN crystals and homoepitaxial layers grown on them are briefly reviewed.

scholarly journals Theoretical Study of InAlN/GaN High Electron Mobility Transistor (HEMT) with a Polarization-Graded AlGaN Back-Barrier Layer

Electronics ◽  
2019 ◽  
Vol 8 (8) ◽  
pp. 885 ◽  
Author(s):  
Yan Gu ◽  
Dongmei Chang ◽  
Haiyan Sun ◽  
Jicong Zhao ◽  
Guofeng Yang ◽  
...  
Keyword(s):  
Electron Mobility ◽  
Theoretical Study ◽  
Lattice Relaxation ◽  
High Electron Mobility Transistor ◽  
High Electron ◽  
Two Dimensional ◽  
Drift Diffusion ◽  
High Electron Mobility ◽  
Al Content ◽  
Dimensional Electron Gas

An inserted novel polarization-graded AlGaN back barrier structure is designed to enhance performances of In0.17Al0.83N/GaN high electron mobility transistor (HEMT), which is investigated by the two-dimensional drift-diffusion simulations. The results indicate that carrier confinement of the graded AlGaN back-barrier HEMT is significantly improved due to the conduction band discontinuity of about 0.46 eV at interface of GaN/AlGaN heterojunction. Meanwhile, the two-dimensional electron gas (2DEG) concentration of parasitic electron channel can be reduced by a gradient Al composition that leads to the complete lattice relaxation without piezoelectric polarization, which is compared with the conventional Al0.1Ga0.9N back-barrier HEMT. Furthermore, compared to the conventional back-barrier HEMT with a fixed Al-content, a higher transconductance, a higher current and a better radio-frequency performance can be created by a graded AlGaN back barrier.

Layer-by-Layer Growth Control of Metal–Organic Framework Thin Films Assembled on Polymer Films

2020 ◽  
Vol 12 (45) ◽  
pp. 50784-50792
Author(s):  
Hiroaki Ohara ◽  
Shunsuke Yamamoto ◽  
Daiki Kuzuhara ◽  
Tomoyuki Koganezawa ◽  
Hidetoshi Oikawa ◽  
...  
Keyword(s):  
Thin Films ◽  
Polymer Films ◽  
Metal Organic Framework ◽  
Growth Control ◽  
Layer Growth ◽  
Layer By Layer ◽  
Metal Organic ◽  
Organic Framework

scholarly journals Investigation of AlGaN/GaN Heterostructures Grown on Sputtered AlN Templates with Different Nucleation Layers

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4050 ◽  
Author(s):  
Chuan-Yang Liu ◽  
Ya-Chao Zhang ◽  
Sheng-Rui Xu ◽  
Li Jiang ◽  
Jin-Cheng Zhang ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Optimal Growth ◽  
Growth Conditions ◽  
Layer Growth ◽  
Organic Chemical ◽  
Propagation Mechanism ◽  
Nucleation Layer ◽  
Low Dislocation Density ◽  
Structural And Electrical Properties ◽  
Metal Organic

In this work, a sputtered AlN template is employed to grow high-quality AlGaN/GaN heterostructures, and the effects of AlN nucleation layer growth conditions on the structural and electrical properties of heterostructures are investigated in detail. The optimal growth condition is obtained with composited AlN nucleation layers grown on a sputtered AlN template, resulting in the smooth surface morphology and superior transport properties of the heterostructures. Moreover, high crystal quality GaN material with low dislocation density has been achieved under the optimal condition. The dislocation propagation mechanism, stress relief effect in the GaN grown on sputtered AlN, and metal organic chemical vapor deposition AlN nucleation layers are revealed based on the test results. The results in this work demonstrate the great potential of AlGaN/GaN heterostructures grown on sputtered AlN and composited AlN nucleation layers for microelectronic applications.

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

Coatings ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 720
Author(s):  
He Guan ◽  
Shaoxi Wang
Keyword(s):  
Metal Oxide ◽  
Leakage Current ◽  
Photoelectron Spectroscopy ◽  
Metal Oxide Semiconductor ◽  
Schottky Emission ◽  
Oxide Semiconductor ◽  
Optimized Design ◽  
Mos Capacitors ◽  
Leakage Mechanism ◽  
High K

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.

scholarly journals Electrostatic Design of Polar Metal–Organic Framework Thin Films

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2420
Author(s):  
Giulia Nascimbeni ◽  
Christof Wöll ◽  
Egbert Zojer
Keyword(s):  
Thin Films ◽  
Electrostatic Potential ◽  
Energy Gap ◽  
Dipole Moments ◽  
Metal Organic Framework ◽  
Solid Substrate ◽  
Layer Growth ◽  
Layer By Layer ◽  
Metal Organic ◽  
Linker Molecules

In recent years, optical and electronic properties of metal–organic frameworks (MOFs) have increasingly shifted into the focus of interest of the scientific community. Here, we discuss a strategy for conveniently tuning these properties through electrostatic design. More specifically, based on quantum-mechanical simulations, we suggest an approach for creating a gradient of the electrostatic potential within a MOF thin film, exploiting collective electrostatic effects. With a suitable orientation of polar apical linkers, the resulting non-centrosymmetric packing results in an energy staircase of the frontier electronic states reminiscent of the situation in a pin-photodiode. The observed one dimensional gradient of the electrostatic potential causes a closure of the global energy gap and also shifts core-level energies by an amount equaling the size of the original band gap. The realization of such assemblies could be based on so-called pillared layer MOFs fabricated in an oriented fashion on a solid substrate employing layer by layer growth techniques. In this context, the simulations provide guidelines regarding the design of the polar apical linker molecules that would allow the realization of MOF thin films with the (vast majority of the) molecular dipole moments pointing in the same direction.

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