Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...

When group-III nitrides go infrared: New properties and perspectives

Transition metal oxides – Thermoelectric properties

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.

Valence band splittings and band offsets of AlN, GaN and InN.

20) a-plane] is thoroughly investigated. We find that for the relaxed surfaces of the binary nitrides the difference in electron affinities between m- and a-plane is less than 0.1 eV. The absolute electron affinities are found to strongly depend on the choice of XC functional. However, we find that relative alignments are less sensitive to the choice of XC functional. In particular, we find that relative alignments may be calculated based on Perdew–Becke–Ernzerhof [J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 134, 3865 (1996)] surface calculations with the HSE06 lattice parameters. For InGaN we find that the VBM is a linear function of In content and that the majority of the band-gap bowing is located in the CBM. Based on the calculated electron affinities we predict that InGaN will be suited for water splitting up to 50% In content. © 2011 American Institute of Physics. [doi:10.1063/1.3548872]

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Hybrid functional investigations of band gaps and band alignments for AlN, GaN, InN, and InGaN.

Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor that has attracted a large amount of interest due to its ultra-large bandgap of 4.8 eV, a high breakdown field of 8 MV/cm, and high thermal stability. These properties enable Ga2O3 a promising material for a large range of applications, such as high power electronic devices and solar-blind ultraviolet (UV) photodetectors. In the past few years, a significant process has been made for the growth of high-quality bulk crystals and thin films and device optimizations for power electronics and solar blind UV detection. However, many challenges remain, including the difficulty in p-type doping, a large density of unintentional electron carriers and defects/impurities, and issues with the device process (contact, dielectrics, and surface passivation), and so on. The purpose of this article is to provide a timely review on the fundamental understanding of the semiconductor physics and chemistry of Ga2O3 in terms of electronic band structures, optical properties, and chemistry of defects and impurity doping. Recent progress and perspectives on epitaxial thin film growth, chemical and physical properties of defects and impurities, p-type doping, and ternary alloys with In2O3 and Al2O3 will be discussed.

Recent progress on the electronic structure, defect, and doping properties of Ga2O3

duced using a vapor transport technique. 3 The calculations on which this work is based used a parabolic conduction band and an electron effective mass of 0.14m0. No justification for the choice of effective mass value was given and though the author concluded that the interpretation of the thermoreflectance spectra is qualitatively correct, it was suggested that the inclusion of the effects of conduction band nonparabolicity may produce better agreement with the data. In this paper, the room temperature bandgap and the band-edge effective mass of single crystal epitaxially grown CdO are determined from infrared reflectivity, ultraviolet/ visible optical absorption and Hall effect measurements. The nonparabolicity of the conduction band and the competing effects of Moss-Burstein band-filling and bandgap renormalization are explicitly considered. Single crystal CdO samples were grown by metalorganic vapor-phase epitaxy MOVPE on r-plane sapphire substrates using the growth precursors tertiary butanol and dimethylcadmium. Further details on the growth and structural characterization of these samples can be found elsewhere. 4 The samples were annealed under ultrahigh vacuum at a temperature of 400 °C for between 2 and 24 h. As a result of this annealing, the free electron concentrations mobilites were reduced increased from 1.8 10 20 cm 3 51 cm 2 V 1 s 1 , for the as-grown samples, to as low high as 4.410 19 cm 3 113 cm 2 V 1 s 1 for the postgrowth annealed samples. Infrared reflectivity measurements were made using a Perkin Elmer Spectrum GX Fourier transform infrared spectrometer with a 35° specular reflection with respect to the surface normal. The reflectance was determined from the ratio of the reflection from the CdO sample and that of a high reflectivity optical mirror. The system employs a cadmium mercury telluride detector giving a working range of 0.05‐1.24 eV. Transmission geometry ultraviolet/visible absorption measurements were performed using a Perkin Elmer Lambda 25 spectrometer working between 1.24 and 4.00 eV. All measurements from both optical systems were taken at room temperature. Finally, single field Hall effect measurements, also conducted at room temperature, were performed using the standard van der Pauw method. The infrared reflectivity spectra of three CdO samples are shown in Fig. 1. The spectra were simulated using an expression describing the propagation and reflection of electromagnetic radiation from a two-layer stratified medium derived from the Fresnel equations. 5 This expression is dependent on the complex refractive indices n of the materials which are described in terms of the two-oscillator dielectric

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Bandgap and effective mass of epitaxial cadmium oxide

Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Г-point conduction band minimum lying
significantly below the charge neutrality level.

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Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces

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.

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Valence band offset of InN∕AlN heterojunctions measured by x-ray photoelectron spectroscopy

The valence band offset of ZnO/AlN heterojunctions is determined by high resolution x-ray photoemission spectroscopy. The valence band of ZnO is found to be 0.43±0.17 eV below that of AlN. Together with the resulting conduction band offset of 3.29±0.20 eV, this indicates that a type-II (staggered) band line up exists at the ZnO/AlN heterojunction. Using the III-nitride band offsets and the transitivity rule, the valence band offsets for ZnO/GaN and ZnO/InN heterojunctions are derived as 1.37 and 1.95 eV, respectively, significantly higher than the previously determined values.

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Valence band offset of the ZnO/AlN heterojunction determined by x-ray photoemission spectroscopy

The influence of Sn doping on the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy has been investigated over a range of substrate temperatures between 650 and 900 degrees C The extent of dopant incorporation under a constant Sn flux decreases monotonically with increasing substrate temperature, although the n-type carrier concentration in "overdoped" films grown at 650 degrees C is lower than in films with a lower Sn concentration grown at 750 degrees C The small increase in lattice parameter associated with Sn doping leads to improved matching with the substrate and suppresses breakup of the films into square islands observed in high temperature growth of undoped In2O3 on Y-stabilized ZrO2(100) Plasmon energies derived from infrared reflection spectra of Sn-doped films are found to be close to satellite energies in core level photoemission spectroscopy, but for a nominally undoped reference sample there is evidence for carrier accumulation at the surface This influences both the In 3d core line shape and the intensity of a peak close to the Fermi energy associated with photoemission from the conduction band

Philip David King

Papers

Bandgap and effective mass of epitaxial cadmium oxide

Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces

Valence band offset of InN∕AlN heterojunctions measured by x-ray photoelectron spectroscopy

Valence band offset of the ZnO/AlN heterojunction determined by x-ray photoemission spectroscopy

The influence of Sn doping on the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy