Influence of fabrication steps on optical and electrical properties of InN thin films (original) (raw)
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Annealing studies on InN thin films grown by modified activated reactive evaporation
2009
We describe the effect of annealing in air and in vacuum on structural, electrical and optical properties of indium nitride (InN) thin films. The films were grown by modified activated reactive evaporation. Films annealed in air were transformed to In 2 O 3 at 450 1C whereas films annealed in vacuum started decomposing at 500 1C. The c-lattice constant was found decreasing for increasing annealing temperature due to reduction of excess nitrogen in the films. The major changes in structural, electrical and optical properties appear around 400 1C. Both air and vacuum-annealed films show a reduction in the carrier concentration with annealing, explaining the observed reduction in bandgap (Moss-Burstein shift) for vacuum-annealed films. For air-annealed films, the bandgap increases when annealed, which may be due to oxynitride formation overcoming the effect of reduced carrier concentration. A decrease in the photoluminescence intensity was observed at 400 1C for air-annealed and 500 1C for vacuumannealed films which can be attributed, respectively, to the presence of indium oxide and indium in the films. Optimal annealing temperature was observed between 400 and 450 1C in vacuum.
Structural and optical characterisation of InN layers grown by MOCVD
2004
In the following, we report investigations of the dependencies of the structural, optical and electrical characteristics of InN thin films grown by MOCVD on the growth temperature. The layer thicknesses range from 70 to 400 nm. Their carrier concentrations range from 7 × 10 18 to 4 × 10 19 cm −3 . Hall mobility values from 150 to 1300 cm 2 /V/s were determined in these films. The variation of the growth temperature and V/III ratio brought about different growth modes and rates. Using TEM, in addition to measuring layer thickness, we also determined the growth mode along with the structural quality of the InN layers. The surface roughness was obtained from AFM measurements. The layer crystalline quality was also investigated by means of X-ray diffraction in the rocking mode. Photoluminescence measurements performed at room temperature and at 7 K gave emission at around 0.7 eV.
Journal of Applied Physics, 2013
Transmission electron microscopy has been employed to analyze the direct nucleation and growth, by plasma-assisted molecular beam epitaxy, of high quality InN (0001) In-face thin films on (111) Si substrates. Critical steps of the heteroepitaxial growth process are InN nucleation at low substrate temperature under excessively high N-flux conditions and subsequent growth of the main InN epilayer at the optimum conditions, namely, substrate temperature 400-450 C and In/N flux ratio close to 1. InN nucleation occurs in the form of a very high density of three dimensional (3D) islands, which coalesce very fast into a low surface roughness InN film. The reduced reactivity of Si at low temperature and its fast coverage by InN limit the amount of unintentional Si nitridation by the excessively high nitrogen flux and good bonding/adhesion of the InN film directly on the Si substrate is achieved. The subsequent overgrowth of the main InN epilayer, in a layer-by-layer growth mode that enhances the lateral growth of InN, reduces significantly the crystal mosaicity and the density of threading dislocations is about an order of magnitude less compared to InN films grown using an AlN/GaN intermediate nucleation/buffer layer on Si. The InN films exhibit the In-face polarity and very smooth atomically stepped surfaces. V
Growth of high-quality InN using low-temperature intermediate layers by RF-MBE
Journal of Crystal Growth, 2002
InN with a film thickness of 600 nm was grown on a (0 0 0 1) sapphire substrate using low-temperature-grown intermediate layers by radio frequency plasma-excited molecular beam epitaxy (RF-MBE). From SEM observation, it was found that InN films with uniform surface morphology were grown. The electron mobility at room temperature obtained in this study was 830 cm 2 /V s and the corresponding carrier density was 1:0 Â 10 19 cm À3 : To our knowledge, this electron mobility is the highest value ever reported for single-crystal InN films. r
Energy relaxation of InN thin films
Applied Physics Letters, 2007
The energy relaxation of InN thin films has been studied by ultrafast time-resolved photoluminescence technique. The obtained carrier cooling curves can be explained by carriers releasing excessive energy through the carrier-LO-phonon interaction. The extracted effective phonon emission times decrease as the photoexcited carrier concentration reduces and come close to the theoretical prediction of 23 fs at small carrier concentration. The reduction of energy loss rate at high photoexcited carrier density is attributed to the hot phonon effect.
The microstructure and properties of InN layers
physica status solidi (c), 2010
A series of InN layers grown by different techniques has been investigated by transmission electron microscopy, photoluminescence and Raman spectroscopy. The polarity is shown to be determined by the underlying GaN template. In these In polar layers, the c-screw dislocations density is low and that of a-type dislocations is in the high-10 9 cm-2 range. The dislocation density tends to decrease towards the surface. Along the first 0.5 µm, and particularly in the samples grown by hydride vapour epitaxy, we observe a large number of stacking faults, which probably contribute to the dislocation density reduction. The optical band gap in MBE and MOVPE samples is between 0.6 and 0.7 eV, but that of the HVPE templates is above 1 eV. Estimations from Raman data show that this behaviour correlates well with the residual carrier concentration.
Characterizations of InN thin films grown on Si (110) substrate by reactive sputtering
2011
Indium nitride (InN) thin films were deposited onto Si (110) by reactive sputtering and pure In target at ambient temperature. The effects of the Ar-N 2 sputtering gas mixture on the structural properties of the films were investigated by using scanning electron microscope, energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction techniques. The optical properties of InN layers were examined by micro-Raman and Fourier transform infrared (FTIR) reflectance spectroscopy at room temperature. Structural analysis specified nanocrystalline structure with crystal size of 15.87 nm, 16.65 nm, and 41.64 nm for InN films grown at N 2 /Ar ratio of 100/0, 75/25, and 50/50, respectively. The Raman spectra indicates well defined peaks at 578, 583, and 583 cm −1 , which correspond to the A 1 (LO) phonon of the hexagonal InN films grown at gas ratios of 100 : 0, 75 : 25 and 50 : 50 N 2 : Ar, respectively. Results of FTIR spectroscopy show the clearly visible TO [E 1 (TO)] phonon mode of the InN at 479 cm −1 just for film that were deposited at 50 : 50 N 2 : Ar. The X-ray diffraction results indicate that the layers consist of InN nanocrystals. The highest intensity of InN (101) peak and the best nanocrystalline InN films can be seen under the deposition condition with N 2 /Ar gas mixture of 50 : 50.
Morphology and surface electronic structure of MBE grown InN
Journal of Crystal Growth, 2007
The morphology and surface electronic structure of indium nitride films grown by plasma-induced molecular beam epitaxy have been studied using atomic force microscopy as well as X-ray and ultraviolet photoelectron spectroscopy. Valence band and In4d core level spectra were measured as a function of excitation energy (He I, He II and AlKa radiation) on samples with minimised exposure to ambient conditions after growth (30 s). A work function of 4.1 eV was determined and the onset of the valence band is located 1.6 eV below the Fermi level which is a strong indication of the already discovered electron accumulation at InN surfaces. In addition, the theoretically predicted InN valence states were observed. At the outermost InN surface the In4d level seems to consist of two components, where the existence of a metallic phase can be ruled out by a comparison with sputtered InN samples and measurements performed on an indium foil. r
Optical and structural properties of InN grown by HPCVD
2009
The optical and structural properties of InN layers grown by 'High Pressure Chemical Vapor Deposition' (HPCVD) using a pulsed precursor approach have been studied. The study focuses on the effect of ammonia precursor exposure time and magnitude on the InN layer quality. The samples have been analyzed by X-ray diffraction, Raman scattering, infra red reflectance spectroscopy and photoluminescence spectroscopy. Raman measurements and X-ray diffraction showed the grown layers to be single phase InN of high crystalline quality. The E 2 (high) Raman mode showed FWHM's as small as 9.2 cm -1 . The FWHM's of the InN(0002) X-ray Bragg reflex in the 2Θ-Ω-scans were around 350 arcsec, with rocking curve values as low as 1152 arcsec Photoluminescence features have been observed down to 0.7 eV, where the low energy cutoff might be due to the detector limitation. The analysis of the IR reflectance spectra shows that the free carrier concentrations are as low as 3.3·10 18 cm -3 for InN layers grown on sapphire substrates.
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.