Binary group III-nitride based heterostructures: band offsets and transport properties
TL;DR: In this paper, the growth of non-polar III-nitrides has been an important subject due to its potential improvement on the efficiency of III-nodes-based opto-electronic devices.
Abstract: In the last few years, there has been remarkable progress in the development of group III-nitride based materials because of their potential application in fabricating various optoelectronic devices such as light emitting diodes, laser diodes, tandem solar cells and field effect transistors. In order to realize these devices, growth of device quality heterostructures are required. One of the most interesting properties of a semiconductor heterostructure interface is its Schottky barrier height, which is a measure of the mismatch of the energy levels for the majority carriers across the heterojunction interface. Recently, the growth of non-polar III-nitrides has been an important subject due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices. It is well known that the c-axis oriented optoelectronic devices are strongly affected by the intrinsic spontaneous and piezoelectric polarization fields, which results in the low electron-hole recombination efficiency. One of the useful approaches for eliminating the piezoelectric polarization effects is to fabricate nitride-based devices along non-polar and semi-polar directions. Heterostructures grown on these orientations are receiving a lot of focus due to enhanced behaviour. In the present review article discussion has been carried out on the growth of III-nitride binary alloys and properties of GaN/Si, InN/Si, polar InN/GaN, and nonpolar InN/GaN heterostructures followed by studies on band offsets of III-nitride semiconductor heterostructures using the x-ray photoelectron spectroscopy technique. Current transport mechanisms of these heterostructures are also discussed.
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01 Mar 1997
TL;DR: In this article, first principles electronic structure calculations on wurtzite AlN, GaN, and InN reveal crystal field splitting parameters ΔCF of −217, 42, and 41 meV, respectively.
Abstract: First‐principles electronic structure calculations on wurtzite AlN, GaN, and InN reveal crystal‐field splitting parameters ΔCF of −217, 42, and 41 meV, respectively, and spin–orbit splitting parameters Δ0 of 19, 13, and 1 meV, respectively. In the zinc blende structure ΔCF≡0 and Δ0 are 19, 15, and 6 meV, respectively. The unstrained AlN/GaN, GaN/InN, and AlN/InN valence band offsets for the wurtzite (zinc blende) materials are 0.81 (0.84), 0.48 (0.26), and 1.25 (1.04) eV, respectively. The trends in these spectroscopic quantities are discussed and recent experimental findings are analyzed in light of these predictions.
274 citations
TL;DR: In this paper, the fundamental mechanism and interfacial charge transfer dynamics in TiO2/graphene nanocomposites are reviewed and the design strategies of various graphene-based hybrids are highlighted along with some specialized synthetic routes adopted to attain preferred properties.
103 citations
TL;DR: In this article, a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants is presented, with a particular focus on the main experimental conditions employed in the photo-electrocatalytic degradation of various contaminants.
Abstract: Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.
53 citations
TL;DR: In this article, a novel nanowire structure adopting a graded-index separate confinement heterostructure (GRINSCH) in which the active region is sandwiched between two compositionally graded AlGaN layers, namely, a GRINSCH diode, is proposed.
Abstract: High-density dislocations in materials and poor electrical conductivity of p-type AlGaN layers constrain the performance of the ultraviolet light emitting diodes and lasers at shorter wavelengths. To address those technical challenges, we design, grow, and fabricate a novel nanowire structure adopting a graded-index separate confinement heterostructure (GRINSCH) in which the active region is sandwiched between two compositionally graded AlGaN layers, namely, a GRINSCH diode. Calculated electronic band diagram and carrier concentrations show an automatic formation of a p–n junction with electron and hole concentrations of ∼1018 /cm3 in the graded AlGaN layers without intentional doping. The transmission electron microscopy experiment confirms the composition variation in the axial direction of the graded AlGaN nanowires. Significantly lower turn-on voltage of 6.5 V (reduced by 2.5 V) and smaller series resistance of 16.7 Ω (reduced by nearly four times) are achieved in the GRINSCH diode, compared with the ...
48 citations
TL;DR: In this paper , the morphology and structure of these materials influence on the sensor response, and challenges and future perspectives for ZnO chemiresistive sensors are also discussed, focusing on how the morphology of the materials can influence on sensor response.
Abstract: Chemiresistive gas sensors have been widely applied to monitor analytes of environmental, food and health importance. Among the plethora of materials that can be used for designing chemiresistive sensors, ZnO is one of the most explored for gas sensing, as this material has a low-cost, is non-toxic and can be easily obtained through standard chemical synthesis. Adding to this, ZnO can form heterostructures capable to improve sensor performance regarding sensitivity, selectivity and stability. Moreover, ZnO heterostructures also contribute to lower operating temperature of gas sensors, since the synergistic effects contribute to amplify the sensor signal. In this review, we survey recent advances on different types of chemiresistive ZnO-based gas sensors, focusing on how the morphology and structure of these materials influence on the sensor response. Challenges and future perspectives for ZnO chemiresistive sensors are also discussed.
47 citations
References
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TL;DR: In this paper, the authors measured the valence-band offsets (VBOs) of wurtzite C-plane and A-plane AlN/GaN heterojunctions by X-ray photoelectron spectroscopy.
Abstract: We have directly measured the valence-band offsets (VBOs) of wurtzite C-plane and A-plane AlN/GaN heterojunctions by X-ray photoelectron spectroscopy. The VBOs were determined to be 0.82 ± 0.15 and 0.63 ± 0.15 eV for the C-plane and A-plane AlN/GaN heterojunctions, respectively. The discrepancy in VBOs of heterojunctions with different orientations is mainly due to the spontaneous polarization effect. The VBO of the nonpolar heterojunction is closer to the intrinsic value since the A-plane samples show no polarization effects.
15 citations
TL;DR: In this article, high-quality InGaN/GaN multiple-quantum wells (MQWs) with different In fractions varying from 0.04 to 0.30 have been grown on Ga-polarity GaN by N2 plasma-assisted molecular-beam epitaxy (rf-MBE).
Abstract: High-quality InGaN/GaN multiple-quantum wells (MQWs) with different In fractions varying from 0.04 to 0.30 have been grown on Ga-polarity GaN by N2 plasma-assisted molecular-beam epitaxy (rf-MBE). High-resolution x-ray diffraction results have indicated that the high interface quality and good reproducibility of the InGaN QW have been achieved. Photoluminescence spectra reveals the superior and intense luminescence properties of InGaN MQWs from ultraviolet (∼388 nm) to green-yellow (∼528 nm) range. We have shown that the Ga-polarity GaN underneath is the key parameter for the successful growth of InGaN MQWs by rf-MBE.
15 citations
TL;DR: In this paper, the structural and optical properties of a-plane GaN film grown on a r-plane sapphire substrate by plasma-assisted molecular beam epitaxy were reported.
15 citations
TL;DR: In this paper, the electrical transport properties of InN/GaN heterostructure based Schottky junctions were studied over a wide temperature range of 200-500 K. The barrier height and the ideality factor were calculated from currentvoltage (I-V) characteristics based on thermionic emission (TE), and found to be temperature dependent.
14 citations
TL;DR: In this article, the first-time growth of A-plane GaN on LiGaO 2 using plasma-assisted molecular beam epitaxy was demonstrated, and structural and morphological analysis was performed using X-ray and reflective high energy electron diffraction.
14 citations