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 article, the authors measured the currentvoltage-temperature characteristics of PtSi/p-Si Schottky barrier diodes in the temperature range 60-115 K and determined a mean barrier height at T = 0 K, ƒ b 0 = 223 mV, with an assumed) Gaussian distribution of standard deviation σ ǫ = 12.5 mV.
Abstract: The current-voltage-temperature characteristics of PtSi/p-Si Schottky barrier diodes were measured in the temperature range 60–115 K. Deviation of the ideality factor from unity below 80 K may be modelled using the so-called T0 parameter with T0 = 18 K. It is also shown that the curvature in the Richardson plots may be remedied by using the flatband rather than the zero-bias saturation current density. Physically, the departure from ideality is interpreted in terms of an inhomogeneous Schottky contact. Here we determine a mean barrier height at T = 0 K, ƒ b 0 = 223 mV , with an (assumed) Gaussian distribution of standard deviation σ ƒ = 12.5 mV . These data are correlated with the zero-bias barrier height, ƒ j 0 = 192 mV (at T = 90 K), the photoresponse barrier height, ƒ ph = 205 mV , and the flatband barrier height, ƒ fb = 214 mV . Finally, the temperature coefficient of the flatband barrier was found to be −0.121 mVK−1, which is approximately equal to 1 2 (dE g i /dT) , thus suggesting that the Fermi level at the interface is pinned to the middle of the band gap.
119 citations
TL;DR: In this paper, the authors proposed and demonstrated the fabrication of InN∕GaN multiple quantum well (MQW) consisting of 1 ML and fractional monolayer InN well insertion in GaN matrix under In-polarity growth regime.
Abstract: The authors propose and demonstrate the fabrication of InN∕GaN multiple quantum well (MQW) consisting of 1 ML and fractional monolayer InN well insertion in GaN matrix under In-polarity growth regime. Since the critical thickness of InN epitaxy on GaN is about 1 ML and the growth temperature for 1 ML InN insertion can be remarkably higher, the proposed MQW structure can avoid/reduce generation of misfit dislocation, resulting in higher quality MQW-structure nature in principle than former InN-based MQWs. The proposed InN∕GaN MQWs are potentially applicable to room temperature operating excitonic devices working in short-wavelength visible colors.
118 citations
TL;DR: In this article, the impact of threading dislocation density on Ni∕n-GaN Schottky barrier diode characteristics was investigated using forward biased current-voltage-temperature (I-V-T) and internal photoemission (IPE) measurements.
Abstract: The impact of threading dislocation density on Ni∕n-GaN Schottky barrier diode characteristics is investigated using forward biased current-voltage-temperature (I-V-T) and internal photoemission (IPE) measurements. Nominally, identical metal-organic chemical vapor deposition grown GaN layers were grown on two types of GaN templates on sapphire substrates to controllably vary threading dislocation density (TDD) from 3×107to7×108cm−2. I-V-T measurements revealed thermionic emission to be the dominant transport mechanism with ideality factors near 1.01 at room temperature for both sample types. The Schottky barrier heights showed a similar invariance with TDD, with measured values of 1.12–1.13eV obtained from fitting the I-V-T results to a thermionic emission-diffusion model. The I-V-T results were verified by IPE measurements made on the same diodes, confirming that the Ni∕n-GaN barrier heights do not show a measurable TDD dependence for the TDD range measured here. In apparent contrast to this result is th...
110 citations
TL;DR: In this article, a GaN multiple quantum well (MQW) laser diodes were fabricated on (0001)Si oriented 6H-SiC substrate using low-pressure metal organic vapor phase epitaxy (LP-MOVPE), and the laser oscillation was observed above the threshold current of 800 mA at a peak wavelength of 414.3 nm under pulsed current injection at room temperature.
Abstract: InGaN multiple quantum well (MQW) laser diodes were fabricated on (0001)Si oriented 6H–SiC substrate using low-pressure metal organic vapor phase epitaxy (LP-MOVPE). The laser oscillation was observed above the threshold current of 800 mA at a peak wavelength of 414.3 nm under pulsed current injection at room-temperature. The pulse duration was 300 ns and the repetition frequency was 1 kHz. The threshold current density and differential efficiency were estimated to be 16 kA/cm2 and 0.03 W/A, respectively. The full width at half maximum (FWHM) of the lasing emission lines was between 0.03 nm and 0.21 nm. Streak-shaped far field patterns were clearly observable. The lifetime of the laser diode was more than 5 hours.
110 citations
TL;DR: In this article, the morphology of InGaN epilayers grown by metal-organic vapor phase epitaxy on GaN pseudosubstrates has been examined by atomic force microscopy.
Abstract: The morphology of InGaN epilayers grown by metal-organic vapor phase epitaxy on GaN pseudosubstrates has been examined by atomic force microscopy. The composition of the epilayers has been measured using a combination of secondary ion mass spectrometry and x-ray photoelectron spectroscopy. The dependence of the growth mode on the growth conditions has been investigated. At the lowest temperatures and NH3 fluxes, a two-dimensional island nucleation growth mode is described, in which flat islands form stacks which align along underlying GaN terraces. As the growth temperature is increased a transition to a step-flow growth mode is observed. A transition from two-dimensional island nucleation to step-flow growth may also be achieved by increasing the NH3 flux, or by decreasing the trimethylindium flux. Each transition is discussed in terms of both surface kinetics and indium incorporation into the growing film. A transition from two-dimensional to three-dimensional growth may be induced by an increase in the...
105 citations