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: Deep level transient spectroscopy confirms the presence of native defects with discrete energy levels at GaN and provides support to this interpretation of lateral inhomogeneity of the SBH.
Abstract: The barrier heights (BH) of various metals including Pd, Pt and Ni on n-type GaN (M/n-GaN) have been measured in the temperature range 80–400 K with using a current–voltage (I–V) technique. The temperature dependence of the I–V characteristics of M/n-GaN have shown non-ideal behaviors and indicate the presence of a non-uniform distribution of surface gap states, resulting from the residual defects in the as grown GaN. The surface gap states density Nss, as well as its temperature dependence were obtained from the bias and temperature dependence of the ideality factor n(V,T) and the barrier height ΦBn(V,T). Further, a dependence of zero-bias BH Φ0Bn on the metal work function (Φm) with an interface parameter coefficient of proportionality of 0.47 is found. This result indicates that the Fermi level at the M/n-GaN interface is unpinned. Additionally, the presence of lateral inhomogeneities of the BH, with two Gaussian distributions of the BH values is seen. However, the non-homogeneous SBH is found to be correlated to the surface gap states density, in that Φ0Bn becomes smaller with increasing Nss. These findings suggest that the lateral inhomogeneity of the SBH is connected to the non-uniform distribution of the density of surface gap states at metal/GaN which is attributed to the presence of native defects in the as grown GaN. Deep level transient spectroscopy confirms the presence of native defects with discrete energy levels at GaN and provides support to this interpretation.
99 citations
TL;DR: The thermal decomposition of a gallium tribromide-ammonia complex in an ammonia, argon, or nitrogen atmosphere has been used for the deposition of gallium nitride films on silicon and hexagonal silicon carbide substrates in a gas flow system as discussed by the authors.
Abstract: The thermal decomposition of a gallium tribromide‐ammonia complex in an ammonia, argon, or nitrogen atmosphere has been used for the deposition of gallium nitride films on silicon and hexagonal silicon carbide substrates in a gas flow system. The substrate temperature and the nature of the ambient are the most important parameters of the deposition process. Adherent and transparent films of gallium nitride have been deposited at substrate temperatures up to about 600°C in an ammonia atmosphere and up to about 750°C in a nitrogen or argon ambient. At higher temperatures, the deposit became contaminated with gallium. The gallium nitride films deposited on {111} oriented silicon substrates at 600°–700°C were found to show a (110) fiber orientation. Epitaxial, single crystalline gallium nitride films have been grown successfully on the basal plane of hexagonal silicon carbide substrates at 520°–600°C. These films are of high resistivity indicating that the thermal decomposition of gallium nitride is negligible. Thus, the thermal decomposition of the gallium tribromide‐ammonia complex provides a new promising technique for the crystal growth of gallium nitride.
95 citations
TL;DR: In this paper, the authors studied how electrons drift under the action of an applied electric field within bulk wurtzite indium nitride and found that the optimal cutoff frequency for an ideal indium-nitride-based device ranges from around 10GHz when the device thickness is set to 10μm to about 2.5THz when the devices thickness was set to 0.1μm.
Abstract: We study how electrons, initially in thermal equilibrium, drift under the action of an applied electric field within bulk wurtzite indium nitride. We find that the optimal cutoff frequency for an ideal indium-nitride-based device ranges from around 10GHz when the device thickness is set to 10μm to about 2.5THz when the device thickness is set to 0.1μm. We thus suggest that indium nitride offers great promise for future high-speed device applications.
95 citations
TL;DR: In this article, gate-controlled n+p metaloxide-semiconductor diodes were fabricated in p-GaN using MgO as a gate dielectric and Si+ implantation to create the n+ regions.
Abstract: Gate-controlled n+p metal–oxide–semiconductor diodes were fabricated in p-GaN using MgO as a gate dielectric and Si+ implantation to create the n+ regions. This structure overcomes the low minority carrier generation rate in GaN and allowed observation of clear inversion behavior in the dark at room temperature. By contrast, diodes without the n+ regions to act as an external source of minority carriers did not show inversion even at measurement temperatures of 300 °C. The gated diodes showed the expected shape of the current–voltage characteristics, with clear regions corresponding to depletion and inversion under the gate. The MgO was deposited prior to the Si implantation and was stable during the activation annealing for the Si-implanted n+ regions.
93 citations
TL;DR: In this paper, the valence band offset of wurtzite-InN∕AlN (0001) heterojunctions was determined by x-ray photoelectron spectroscopy to be 1.52±0.17eV.
Abstract: The valence band offset of wurtzite-InN∕AlN (0001) heterojunctions is determined by x-ray photoelectron spectroscopy to be 1.52±0.17eV. Together with the resulting conduction band offset of 4.0±0.2eV, a type-I heterojunction forms between InN and AlN in the straddling arrangement.
93 citations