Band Gap Energy Of InN Research Articles

Structural ordering, morphology and optical properties of amorphous AlxIn1−xN thin films grown by plasma-assisted dual source reactive evaporation

Amorphous aluminum indium nitride (AlxIn1−xN) thin films were deposited on quartz substrates by plasma-assisted dual source reactive evaporation system. In-rich (x=0.10 and 0.18) and Al-rich (x=0.60 and 0.64) films were prepared by simply varying an AC voltage applied to indium wire. The X-ray-diffraction patterns revealed a small broad peak assigned to Al0.10In0.90N (002) plane, but no perceivable peaks assigned to crystalline AlxIn1−xN were observed for the films with x=0.18, 0.60 and 0.64. The morphology of the film was changed from clusters of small grains to uniformly shaped particles with decrease of x. The band gap energy of the films increased from 1.08eV to 2.50eV as the Al composition varied from 0.1 to 0.64. Also, Raman results indicated that E2(high) and A1(LO) peaks of the AlxIn1−xN films are remarkably blue-shifted by increasing x and the A1(LO) phonon mode of the Al-rich films exhibits two-mode behavior. A bowing parameter of 4.3eV was obtained for AlInN films. The extrapolated value from bowing equation was 0.85eV for band gap energy of InN.

Time, energy, and spatially resolved TEM investigations of defects in InGaN

A novel sample preparation technique is reported to fabricate electron transparent samples from devices utilizing a FIB process with a successive wet etching step. The high quality of the obtained samples allows for band gap—and chemical composition measurements of In x Ga 1− x N quantum wells where electron beam induced damage can be controlled and shown to be negligible. The results reveal indium enrichment in nanoclusters and defects that cause fluctuations of the band gap energy and can be measured by low loss Electron Energy Spectroscopy with nm resolution. Comparing our time, energy, and spatially resolved measurements of band gap energies, chemical composition, and their related fluctuations with literature data, we find quantitative agreement if the band gap energy of InN is 1.5–2 eV.

Bandgap energy of InN and its temperature dependence

InN crystals are grown on sapphire substrates by a plasma assisted MBE system. The carrier concentration of the samples are 2 × 1018−1 × 1019 cm–3. Optical transmission and reflectance measurements are performed on these samples in a temperature range of 8–300 K. The resultant spectra are analysed by theoretical spectra based on a LO-phonon plasmon coupling scheme for phonon related factor and non-parabolic conduction band structure for electronic transition factor. The observed absorption edge is estimated to mainly originate from the valence band to conduction band transition rather than defect or impurity related transition on the basis of the electron concentration dependence of the momentum matrix element. The bandgap energy is about 0.63 eV, and increases with the temperature decrease. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Correlation among growth conditions, crystal structures and optical properties of InN

This paper addresses band-gap issues of InN. InN films of various qualities were prepared by radio-frequency plasma-assisted molecular-beam epitaxy (RF-MBE). Correlation among photoluminescence (PL) peak energy, carrier concentration, electron mobility, PL intensity, PL line width, and X-ray rocking curve (XRC) line width indicated that the InN sample with the smallest PL peak energy of ∼0.67 eV (at room temperature) had the highest electron mobility, the strongest PL intensity even with the smallest electron concentration, the sharpest PL and (0002) XRC peaks. Dependence of PL peak energy on carrier concentration can be explained mostly by the Burstein-Moss shift. Temperature dependence of PL peak energy was normal with smaller values at higher temperatures. These experimental results suggest that the PL should originate from fundamental inter-band transitions and not likely from mid-gap levels associated with crystal defects. These results also suggest that the true band-gap energy of InN should be less than 0.67 eV and probably around 0.65 eV at room temperature. This assessment was further supported by In-composition dependence of PL peak energy for In-rich In1–xGaxN films (also grown by RF-MBE), where room temperature PL peak energy exhibited a monotonic and smooth decrease with the increase in In-composition, approaching to ∼ 0.67 eV of InN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Radio frequency-molecular beam epitaxial growth of InN epitaxial films on (0001) sapphire and their properties

Growth of InN by radio frequency plasma-excited molecular beam epitaxy on (0001) sapphire was systematically studied. To improve the crystalline quality of InN, the following growth conditions were found to be essential: (1) nitridation of sapphire, (2) two-step growth, (3) precise control of V/III ratio, and (4) selection of optimum growth temperature. Results of structural characterization using x-ray diffraction, transmission electron microscopy, and extended x-ray absorption fine structure have clearly demonstrated that InN grown in this study had single crystalline with ideal hexagonal wurtzite structure. It is confirmed, however, that the InN had a threading dislocation density on the order of 1010/cm2 and large twist distribution. Photoluminescence studies on these well-characterized InN clearly demonstrated that band-gap energy of InN should be less than 0.67 eV at room temperature.

Recent development of InN RF‐MBE growth and its structural and property characterization

This paper describes studies on high-quality InN growth on sapphire by RF-MBE. Critical procedures to obtain high-quality InN films include (1) nitridation process of sapphire substrates prior to growth, (2) two-step growth method including the growth of a low-temperature InN-buffer layer, (3) precise control of V/III ratio and (4) selection of optimum growth temperature. Detailed structural characterizations by XRD, TEM, Raman scattering and EXAFS indicate that InN films have ideal hexagonal wurtzite structure. Further studies using TEM indicate that the grown InN has an ABAB … stacking sequence without inclusion of the cubic phase. However, threading dislocations with a high density of more than 2×1010 cm−2 and a distinct columnar domain structure are observed. FWHMs of ω−2θ mode XRD and E2(high)-phonon-mode of Raman scattering are as small as 28.9 arcsec and 3.2 cm−1, respectively. True band gap energy of InN is also discussed based on optical characterization results obtained from well-characterized hexagonal InN and InGaN grown in this study. Single-crystalline InN films are obtained on Si substrates by a brief nitridation of the Si substrates. Significant improvement of InN crystal quality on Si substrates by the insertion of an AlN buffer layer is also demonstrated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels

We studied the shape and energy position of near-band-edge photoluminescence spectra of InN epitaxial layers with different doping levels. We found that the experimental spectra of InN layers with moderate doping level can be nicely interpreted in the frames of the ``free-to-bound'' recombination model in degenerate semiconductors. For carrier concentrations above $n>5\ifmmode\times\else\texttimes\fi{}{10}^{18}{\mathrm{cm}}^{\ensuremath{-}3}$ the emission spectra can also be modeled satisfactorily, but a contribution due to a pushing up of nonequilibrium holes over the thermal delocalization level in the valence band tails should be considered in the model. The emission spectra of samples with low doping level were instead explained as a recombination from the bottom of the conduction band to a shallow acceptor assuming the same value of the acceptor binding energy estimated from the spectra of highly doped samples. Analyzing the shape and energy position of the free-electron recombination spectra we determined the carrier concentrations responsible for the emissions and found that the fundamental band gap energy of InN is ${E}_{g}=692\ifmmode\pm\else\textpm\fi{}2\mathrm{meV}$ for an effective mass at the conduction-band minimum ${m}_{n0}{=0.042m}_{0}.$

Single-crystalline InN films with an absorption edge between 0.7 and 2 eV grown using different techniques and evidence of the actual band gap energy

Single crystalline InN films with an absorption edge between 0.7 and 2 eV have been grown using a variety of different techniques, including conventional metal-organic vapor-phase epitaxy (MOVPE), ArF-laser assisted MOVPE (la-MOVPE), and plasma-assisted molecular-beam epitaxy (pa-MBE). Analysis of samples grown using different methods has led to important evidence for determining the actual band gap energy of InN. In an effort to find the origin of the change in absorption edge, this evaluation was focused on the la-MOVPE of InN. This deposition technique enables InN film deposition over a wide range of growth temperatures, ranging from room temperature to a very high temperature (700 °C). Characterization of InN films grown over a wide range of temperatures strongly suggests that oxygen contamination leads to a larger band gap absorption energy value than the actual value, even in the case of single crystalline films. In films grown at low temperatures, oxygen appeared to form an alloy, resulting in a larger absorption edge, whereas, in films grown at high temperatures oxygen was present as a donor, which resulted in a larger absorption edge due to a Burstein–Moss shift.

Band-GaP Energy and Physical Properties of InN Grown by RF-Molecular Beam Epitaxy

ABSTRACTThis paper describes studies on high-quality InN growth on sapphire by RF-MBE. Critical procedures to obtain high-quality InN films were investigated and (1) nitridation process of sapphire substrates prior to growth, (2) precise control of V/III ratio and (3) selection of optimum growth temperature were found to be essential. Detailed structural characterizations by XRD, TEM, Raman scattering and EXAFS indicate that InN films obtained in this study have ideal hexagonal wurtzite structure. FWHMs of ω-2Θ mode XRD and E2(high)-phonon-mode of Raman scattering are as small as 28.9 arcsec and 3.2 cm-1, respectively. True band gap energy of InN is also discussed based on optical characterization results obtained from well-characterized hexagonal InN grown in this study. PbS, instead of InGaAs, was used as a detector for PL study in order to solve the problem coming from the cut-off wavelength of InGaAs detector. Based on these systematic studies on structural and optical property characterizations using high-quality InN, true band-gap energy of InN is suggested to be less than 0.67 eV and approximately 0.65 eV at room temperature. Single-crystalline InN films are also successfully grown on Si substrates by a brief nitridation of the Si substrates. Significant improvement of InN crystal quality on Si substrates by the insertion of an AlN buffer layer is also demonstrated.

Optical Properties of InxGa1?xN with Entire Alloy Composition on InN Buffer Layer Grown by RF-MBE

Optical characterization of In x Ga 1-x N layers was done by photoluminescence, cathodoluminescence and optical absorption measurements. PL emissions less than 1.9 eV were observed from In x Ga 1-x N films with x > 0.53 that showed no phase separation. A bowing parameter of 2.3 eV was obtained from the relationship between PL emission energy and alloy composition. Absorption edge dependence on In composition was similar to the luminescence peak dependence on In composition. These optical properties indicate that the bandgap energy of InN is below 1.0 eV.

Physical properties of InN with the band gap energy of 1.1 eV

We report the electrical and optical properties of undoped and Mg-doped InN grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates. InN has a hexagonal structure and its c-axis is normal to the (0 0 0 1) sapphire surface. The Raman spectra show a strong E 2 (low) mode at 87 cm −1. The band gap energies of the samples are much smaller than 1.9 eV. InN with the band gap energy less than 1.5 eV shows resistivity behavior anomaly below 2.6 K. The relation between the low temperature resistivity anomaly and the band gap energy of InN is discussed.