Infrared study of the absorption edge of β-InN films grown on GaN/MgO structures (original) (raw)
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Journal of Applied Physics, 2013
Effects of pumping on propagation velocities of confined exciton polaritons in GaAs/AlxGa1−xAs double heterostructure thin films under resonant and non-resonant probe conditions J. Appl. Phys. 113, 013514 (2013) Sub-250nm light emission and optical gain in AlGaN materials J. Appl. Phys. 113, 013106 (2013) Nanomechanical and optical properties of highly a-axis oriented AlN films Appl. Phys. Lett. 101, 254102 (2012) 2.8μm emission from type-I quantum wells grown on InAsxP1−x/InP metamorphic graded buffers Appl. Phys. Lett. 101, 251107 (2012) GaN-based platforms with Au-Ag alloyed metal layer for surface enhanced Raman scattering Infrared to vacuum-ultraviolet spectroscopic ellipsometry and far-infrared optical Hall-effect measurements are applied to conclude on successful p-type doping of InN films. A representative set of In-polar Mg-doped InN films with Mg concentrations ranging from 1:2 Â 10 16 cm À3 to 3:9 Â 10 21 cm À3 is investigated. The data are compared and discussed in dependence of the Mg concentration. Differences between n-type and p-type conducting samples are identified and explained. p-type conductivity in the Mg concentration range between 1:1 Â 10 18 cm À3 and 2:9 Â 10 19 cm À3 is indicated by the appearance of a dip structure in the infrared spectral region related to a loss in reflectivity of p-polarized light as a consequence of reduced LO phonon plasmon coupling, by vanishing free-charge carrier induced birefringence in the optical Hall-effect measurements, and by a sudden change in phonon-plasmon broadening behavior despite continuous change in the Mg concentration. By modeling the near-infrared-to-vacuum-ultraviolet ellipsometry data, information about layer thickness, electronic interband transitions, as well as surface roughness is extracted in dependence of the Mg concentration. A parameterized model that accounts for the phonon-plasmon coupling is applied for the infrared spectral range to determine the free-charge carrier concentration and mobility parameters in the doped bulk InN layer as well as the GaN template and undoped InN buffer layer. The optical Hall-effect best-match model parameters are consistent with those obtained from infrared ellipsometry analysis. V C 2013 American Institute of Physics. [http://dx.
Critical thickness of β-InN/GaN/MgO structures
Journal of Applied Physics, 2010
InN films were grown on MgO substrates with a -GaN buffer layer using the gas source molecular beam epitaxy technique. Initially, at typical growth rates from 0.09 to 0.28 ML/sec and at 500°C substrate temperature, the growth was performed in a layer by layer way as revealed by in situ reflection high-energy electron diffraction ͑RHEED͒. In all samples studied, a critical thickness of ϳ5 ML in InN pseudomorphic layer was measured with a frame by frame analysis of RHEED patterns recorded on video. After reaching critical thickness, the InN films undergo a relaxation process, going from two-dimensional growth to three-dimensional, as evidenced by the transformation of the RHEED patterns that change from streaky to spotty. Depending on the In cell temperature, either nanocolumnar InN or flat cubic final films are grown, as can be corroborated by scanning electron microscopy. The experimental critical thickness ͑h c ͒ value of 5 ML is compared to values calculated from different critical thickness models.
Optical properties of InN grown on Si(111) substrate
Physica Status Solidi A-applications and Materials Science, 2010
A comprehensive characterization of the optical properties of wurtzite InN films grown by molecular beam epitaxy on Si(111) substrates is presented. Two types of films are investigated in this work: InN on AlN/Si(111) and InN on GaN/AlN/Si(111). Their properties are compared to a layer deposited on GaN/sapphire substrate. The dielectric function (DF) is obtained from spectroscopic ellipsometry (SE). The infrared studies yield the plasma frequency and thus the electron density, while the interband absorption is probed between 0.56 and 9.8 eV. For InN grown on Si(111) substrate, the absorption onset is slightly shifted to higher energies with respect to the InN film grown on GaN/sapphire which can be attributed to higher electron concentrations. Despite this, strongly pronounced optical transitions due to critical points of the band structure are found in the high-energy part of the DF. It emphasizes the already promising quality of the InN films on silicon. Band-gap renormalization (BGR), band filling, and strain are taken into account in order to estimate the intrinsic band gap of wurtzite InN. For the InN layers on silicon, we get a band gap between 0.66 and 0.685 eV.
Structure and electronic properties of InN and In-rich group III-nitride alloys
Journal of Physics D: Applied Physics, 2006
The experimental study of InN and In-rich InGaN by a number of structural, optical and electrical methods is reviewed. Recent advances in thin film growth have produced single crystal epitaxial layers of InN which are similar in structural quality to GaN films made under similar conditions and which can have electron concentrations below 1 × 10 18 cm −3 and mobilities exceeding 2000 cm 2 (Vs) −1 . Optical absorption, photoluminescence, photo-modulated reflectance and soft x-ray spectroscopy measurements were used to establish that the room temperature band gap of InN is 0.67 ± 0.05 eV. Experimental measurements of the electron effective mass in InN are presented and interpreted in terms of a non-parabolic conduction band caused by the k · p interaction across the narrow gap. Energetic particle irradiation is shown to be an effective method to control the electron concentration, n, in undoped InN. Optical studies of irradiated InN reveal a large Burstein-Moss shift of the absorption edge with increasing n. Fundamental studies of the energy levels of defects in InN and of electron transport are also reviewed. Finally, the current experimental evidence for p-type activity in Mg-doped InN is evaluated.
Band transitions in wurtzite GaN and InN determined by valence electron energy loss spectroscopy
Solid State Communications, 2005
Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7G0.2 eV) and for wurtzite GaN at (3.3G 0.2 eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal.
Bulk Properties of InN Films determined by experiments and theory
Bulk properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first-principles beyond density-functional theory. The quasi-particle aspect is described in the framework of a quasi-particle method (the GW approximation). The calculated band-gap energy is $ 0.8 eV whereas significance in the optical absorption occurs at $ 1.2 eV, which are consistent with both luminescence and absorption results. The Bethe-Salpeter equation is utilized to model the two-particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN.
Influence of defects on the absorption edge of InN thin films: The band gap value
We investigate the optical-absorption spectra of InN thin films whose electron density varies from ϳ10 17 to ϳ 10 21 cm −3 . The low-density films are grown by molecular-beam-epitaxy deposition while highly degenerate films are grown by plasma-source molecular-beam epitaxy. The optical-absorption edge is found to increase from 0.61 to 1.90 eV as the carrier density of the films is increased from low to high density. Since films are polycrystalline and contain various types of defects, we discuss the band gap values by studying the influence of electron degeneracy, electron-electron, electron-ionized impurities, and electron-LO-phonon interaction self-energies on the spectral absorption coefficients of these films. The quasiparticle self-energies of the valence and conduction bands are calculated using dielectric screening within the random-phase approximation. Using one-particle Green's function analysis, we self-consistently determine the chemical potential for films by coupling equations for the chemical potential and the single-particle scattering rate calculated within the effective-mass approximation for the electron scatterings from ionized impurities and LO phonons. By subtracting the influence of self-energies and chemical potential from the optical-absorption edge energy, we estimate the intrinsic band gap values for the films. We also determine the variations in the calculated band gap values due to the variations in the electron effective mass and static dielectric constant. For the lowest-density film, the estimated band gap energy is ϳ0.59 eV, while for the highest-density film, it varies from ϳ0.60 to ϳ 0.68 eV depending on the values of electron effective mass and dielectric constant.
Critical thickness of beta-InN/GaN/MgO structures
Journal of Applied Physics, 2010
InN films were grown on MgO substrates with a β-GaN buffer layer using the gas source molecular beam epitaxy technique. Initially, at typical growth rates from 0.09 to 0.28 ML/sec and at 500 °C substrate temperature, the growth was performed in a layer by layer way as revealed by in situ reflection high-energy electron diffraction (RHEED). In all samples studied, a critical thickness of ˜5 ML in InN pseudomorphic layer was measured with a frame by frame analysis of RHEED patterns recorded on video. After reaching critical thickness, the InN films undergo a relaxation process, going from two-dimensional growth to three-dimensional, as evidenced by the transformation of the RHEED patterns that change from streaky to spotty. Depending on the In cell temperature, either nanocolumnar InN or flat cubic final films are grown, as can be corroborated by scanning electron microscopy. The experimental critical thickness (hc) value of 5 ML is compared to values calculated from different critical thickness models.