High-quality InN Research Articles

Well-Aligned Zn-Doped InN Nanorods Grown by Metal-Organic Chemical Vapor Deposition and the Dopant Distribution

We report the synthesis and characterization of Zn-doped InN nanorods by metal-organic chemical vapor deposition. Electron microscopy images show that the InN nanorods are single-crystalline structures and vertically well-aligned. Energy-dispersive X-ray spectroscopy analyses suggest that Zn ions are distributed nonhomogenously in InN nanorods. Simulations based on diffusion model show that the doping concentration along the radial direction of InN nanorod is bowl-like from the exterior to the interior, the doping concentration decreases, and Such dopant distribution result in a bimodal EDXS spectrum of Zn across the nanorod. The study of the mechanism of doping effect is useful for the design of InN-based nanometer devices. Also, high-quality Zn-doped InN nanorods will be very attractive as building blocks for nano-optoelectronic devices.'

Growth of cubic InN films with high phase purity by pulsed laser deposition

Cubic InN films have been grown on MgO (1 0 0) substrates with cubic GaN buffer layers by pulsed laser deposition (PLD). It has been found that cubic InN (1 0 0) films grow on the GaN (1 0 0)/MgO (1 0 0) structure with an in-plane epitaxial relationship of [0 0 1] InN∥[0 0 1] GaN∥[0 0 1]MgO. The phase purity of a cubic InN film grown at 440 °C was as high as 99% that can probably be attributed to the enhanced surface migration of film precursors in case of PLD. These results indicate that PLD is a suitable technique for the growth of high-quality cubic InN films, and will makes it possible to fabricate optical and electron devices based on cubic InN films.

Microstructure of InN epilayers deposited in a close-coupled showerhead reactor

The microstructure of epitaxial InN layers has been analyzed by high-resolution X-ray diffraction. Various mosaic block parameters like the tilt and twist between the blocks and an estimate of their lateral coherence lengths have been obtained for a large number of InN epitaxial layers deposited under different V/III ratios, temperatures and reactor pressures. Based on the detailed analysis of the microstrain, we have arrived at a set of optimized deposition parameters for InN in a close-coupled showerhead reactor. We also conclude that excessively high V/III ratio, as mentioned in a few earlier reports, is not a prerequisite for the deposition of high-quality InN layers. In fact, all deposition parameters that lead to an increase in the dissociation of ammonia beyond a critical value lead to increase in the screw dislocation density as indicated by an increase in the tilt value. Interestingly, we find that the density of edge dislocation, indicated by the twist value of the epilayers remains nearly the same irrespective of the deposition parameters.

Structural and transport properties of InN grown on GaN by MBE

AbstractIn this work, the growth of InN on GaN substrates by molecular beam epitaxy and the structural and electrical characterization are presented. The quality of InN is found to be a sensitive function of the III/V flux ratio and the substrate temperature. The structural quality of InN is characterized by X‐ray diffraction, and the transport property is characterized by Hall effect measurements. An optimum growth window to obtain high structural quality InN with high electron mobility is observed. A strong correlation between the structural quality and the measured Hall mobility is shown. Transmission electron microscope study of InN shows high dislocation density (∼2 × 1011 cm–2 at 200 nm from the InN/GaN interface), which is the limiting factor for the transport property in InN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of high quality InN on production style PA‐MBE system

AbstractWe have demonstrated step‐flow growth mode of InN, with monolayer height terrace steps (0.281 nm), using a production‐style PA‐MBE system, GEN200®. The surface morphology exhibits the step‐flow features on relatively large areas and the RMS roughness over an area of 5 × 5 μm2 is 1.4 nm. We also investigated the consequences of In droplets formation during the growth and we have found that the vapor‐liquid‐solid growth mechanism generates defective layer areas underneath droplets that have been formed early in the growth process. The Hall mobility of 1µm thick InN layers, grown in such step‐flow mode is slightly higher than 1400 cm2/Vs while for other growth conditions we have obtained mobility as high as 1904 cm2/Vs at room temperature. The samples exhibit high intensity photoluminescence spectra with a band edge that shifts with free‐carrier concentration. For the lowest carrier concentration of 5.6 × 1017 cm‐3 we observe PL emission at ∼0.64 eV. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of high quality InN grown on production-style plasma assisted molecular beam epitaxy system

In this work, the authors report step-flow growth mode of InN on [0001] oriented GaN templates, using a production-style molecular beam epitaxy system, Veeco GEN200®, equipped with a plasma source. Using adaptive growth conditions, they have obtained a surface morphology that exhibits the step-flow features. The root mean squared roughness over an area of 5×5μm2 is 1.4nm with monolayer height terrace steps (0.281nm), based on atomic force microscopy. It has been found that the presence of In droplets leads to defective surface morphology. From x-ray diffraction, they estimate edge and screw dislocation densities. The former is dominant over the latter. Micro-Raman spectra reveal narrow E22 phonon lines consistent with excellent crystalline quality of the epitaxial layers. The Hall mobility of 1μm thick InN layers, grown in step-flow mode, is slightly higher than 1400cm2∕Vs, while for other growth conditions yielding a smooth surface with no well-defined steps, mobility as high as 1904cm2∕Vs at room temperature has been measured. The samples exhibit high intensity photoluminescence (PL) with a corresponding band edge that shifts with free carrier concentration. For the lowest carrier concentration of 5.6×1017cm−3, they observe PL emission at ∼0.64eV.

Optical Hall Effect in Hexagonal InN

Measurements of the optical Hall effect in naturally doped high-quality wurtzite-structure InN thin films by generalized ellipsometry reveal that both the surface and the interior (bulk) free electron densities decrease with powerlaw dependencies on the film thickness. We discover a significant deviation between the bulk electron and dislocation densities. This difference is attributed here to the existence of surface defects with activation mechanism different from bulk dislocations and identifies the possible origin of the so far persistent natural n-type conductivity in InN. We further quantify the anisotropy of the C-point effective mass.

Growth of InN on Ge(1 1 1) by molecular beam epitaxy using a GaN buffer

Many novel applications are foreseen for the InN-containing materials especially when cheap, conductive substrates can be used. In this paper, we report on the growth of pure InN layers on germanium (Ge) (1 1 1) substrates. We found that high-quality InN can be grown on Ge(1 1 1) with plasma-assisted molecular beam epitaxy when using a thin GaN intermediate layer. On such intermediate GaN layers, 50 nm InN layers were grown and analyzed by RHEED, XRD, AFM, Hall and I– V measurements. Additionally, using ellipsometry we could determine that the optical bandgap of these InN layers lies around 0.85 eV. Our results indicate that Ge(1 1 1) is a promising substrate for vertical conducting devices, with In(Ga)N on top.

Anomalous Optical Properties of InN Nanobelts: Evidence of Surface Band Bending and Photoelastic Effects

The properties of high-quality InN nanobelts fabricated by the metal-organic chemical vapor deposition technique are investigated. The figure shows the uniaxial strain ϵ3 (, solid squares) and in-plane strain ϵ1 (solid circles) as a function of excitation intensity. The reduction of the tensile in-plane strain gives rise to a noticeable increase of the band gap energy.

Synthesis and Properties of High-Quality InN Nanowires and Nanonetworks

We report on the growth of high-quality InN nanowires by the vapor–liquid–solid mechanism at rates of up to 30 μm/h. Smooth and horizontal nanowire growth has been achieved only with nanoscale catalyst patterns, while large-area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires grow along the [110] direction with diameters of 20 to 60 nm and lengths of 5 to 15 μm. The nanowires bend spontaneously or get deflected from other nanowires at angles that are multiples of 30°, forming nanonetworks. The gate-bias-dependent mobility of the charge carriers ranges from 55 cm2/V s to 220 cm2/V s, and their concentration is ∼1018 cm−3.

Phonon-plasmon coupling in electron surface accumulation layers in InN nanocolumns

Raman measurements in high quality InN nanocolumns display a coupled LO phonon-plasmon mode together with uncoupled phonons. The coupled mode is attributed to the spontaneous accumulation of electrons on the lateral surfaces of the nanocolumns. For increasing growth temperature, the electron density decreases as the growth rate increases. The present results indicate that electron accumulation layers do not only form on polar surfaces of InN but also occur on nonpolar ones. According to recent calculations, we attribute the electron surface accumulation to the temperature dependent In-rich surface reconstruction on the nanocolumn sidewalls.

Raman scattering by longitudinal optical phonons in InN nanocolumns grown on Si(1 1 1) and Si(0 0 1) substrates

Raman measurements in high-quality InN nanocolumns and thin films grown on both Si(1 1 1) and Si(1 0 0) substrates display a low-energy coupled LO phonon–plasmon mode together with uncoupled longitudinal optical (LO) phonons. The coupled mode is attributed to the spontaneous accumulation of electrons on the lateral surfaces of the nanocolumns, while the uncoupled ones originates from the inner part of the nanocolumns. The LO mode in the columnar samples appears close to the E 1(LO) frequency. This indicates that most of the incident light is entering through the lateral surfaces of the nanocolumns, resulting in pure longitudinal–optical mode with quasi-E 1 symmetry. For increasing growth temperature, the electron density decreases as the growth rate increases. The present results indicate that electron accumulation layers do not only form on polar surfaces of InN, but also occur on non-polar ones. According to recent calculations, we attribute the electron surface accumulation to the temperature dependent In-rich surface reconstruction on the nanocolumns sidewalls.

Growth of InN films on spinel substrates by pulsed laser deposition

AbstractWe have grown InN films on MgAl2O4(111) substrates with atomically flat surfaces using pulsed laser deposition (PLD) and compared their structural properties with those grown on (Mn,Zn)Fe2O4(111) substrates. It has been revealed that InN(0001) films grow on MgAl2O4(111) with an in‐plane epitaxial relationship of InN[1$ \bar 1 $00] // MgAl2O4[1$ \bar 1 $0], achieving a lattice mismatch minimum. The InN films exhibited a clear sixfold rotational symmetry, without 30° rotational domains and with a full width at half maximum value of the InN 0002 rocking curve being 17.5 arcmin. Comparison between InN films grown on MgAl2O4 and those on (Mn,Zn)Fe2O4 led us to conclude that suppression of the interfacial reactions between the InN films and the substrate is inherently important to obtain high quality InN on substrates with a spinel structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InN Nanostructured Materials: Controlled Synthesis, Characterizations, and Applications

InN 1D materials were successfully grown by metal-organic vapor phase epitaxy (MOVPE) and non-catalytic, template-free hydride metal-organic vapor phase epitaxy (H-MOVPE) on Si, GaN, and c-Al2O3 substrates. Dislocation-free, high-quality InN nanorods with [00.1] growth axis were formed via an apparent vapor-solid (VS) growth mechanism by H-MOVPE. On a contrary when conventional MOVPE was employed InN nanowires were grown via vapor-liquid-solid (VLS) mechanism. The controlled growth of self-seeded III-Nitride nanostructured materials has been demonstrated.

Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy

High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin SixNy at the InN nanocolumn/substrate interface because of Si nitridation. The SixNy thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free.

Evidence of electron accumulation at nonpolar surfaces of InN nanocolumns

High-quality InN nanocolumns grown by molecular beam epitaxy on n-type Si(111) have been electrically characterized by atomic force microscopy. Current-voltage characteristics were measured on InN nanocolumns with similar heights but different diameters. The conductivity scales the nanocolumns reciprocal diameter, pointing to the nanocolumn lateral surface as the main conduction path. These results, opposing those found in undoped GaN nanocolumns where the conductivity is rather independent of the diameter (conduction through the volume), agree well with a model that predicts electron accumulation by Fermi level pinning within the conduction band on nonpolar (m plane) InN surfaces reconstructed under In-rich conditions.

Prevention of In droplets formation by HCl addition during metal organic vapor phase epitaxy of InN

The low decomposition temperature of InN and relatively high thermal stability of NH3 necessitate the use of a high NH3∕TMIn ratio to prevent In droplet formation on the surface. This work shows that the addition of Cl in the form of HCl (Cl∕In molar ratio range of 0.3–1.4) to the growth chamber allows the growth of high quality InN films without the formation of a second In phase at a very low value of the N∕In molar inlet ratio (2500). Photoluminescence spectra in the temperature range of 144to4.5K showed a broad spectral band with a cutoff energy close to the reported minimum of the InN band gap energy (0.65eV).

High current density InN∕AlN heterojunction field-effect transistor with a SiNx gate dielectric layer

In N ∕ Al N metal-insulator-semiconductor heterojunction field-effect transistors with a gate-modulated drain current and a clear pinch-off characteristic have been demonstrated. The devices were fabricated using high-quality InN (26nm)∕AlN (100nm) epifilms grown by plasma-assisted molecular-beam epitaxy on Si (111) substrates. The devices exhibited a current density higher than ∼530mA∕mm with a 5μm gate length. The pinch-off voltage was at ∼−7V with an associated drain leakage current less than 10μA∕mm. The observed high current density may be attributed to the high sheet carrier density due to the large spontaneous polarization difference between InN and AlN.

Controlled synthesis of single-crystalline InN nanorods

Single-crystalline InN nanorods were successfully grown onc-Al2O3, GaN, Si(111), and Si(100) substrates by non-catalytic, template-free hydridemetal–organic vapour phase epitaxy (H-MOVPE). It was evaluated thermodynamicallyand confirmed experimentally that the domain of nanorod growth lies in thevicinity of the growth–etch transition. Stable gas phase oligomer formationis suggested as the nucleation mechanism for InN nanoparticle generation.Dislocation-free, high-quality InN nanorods with [00.1] growth axis were formed viaan apparent solid–vapour growth mechanism. The nanorod diameter, density,and orientation were controlled by growth temperature, substrate selection, andHCl/TMIn and N/In inlet molar ratios.

Synthesis and Characterization of High Quality InN Nanowires and Nano-networks

ABSTRACTHigh quality InN nanowires have been synthesized in a horizontal quartz-tube furnace through direct reaction between metallic Indium and Ammonia using Nitrogen as the carrier gas. Thin film of Au on SiO2/Si substrate has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The nanowires were grown at a very fast rate of up to 30 μm/hr. Smooth and horizontal nanowire growth was achieved only with nanoscale catalyst patterns, while large area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires, which were usually covered with a thin shell layer of In2O3, grew along [110] direction, with overall diameters 20 - 60 nm and lengths 5 - 15 μm. The synthesized nanowires bent spontaneously or got deflected from other nanowires at multiples of 30 degrees forming nano-networks. The catalyst particles for the NWs were found mostly at the sides of the NW apex which helped them to bend spontaneously or get deflected from other NWs at angles which were multiples of 30 degrees. The NW based FETs with a back-gated configuration have already been investigated. The gate-bias dependent mobility of the NWs ranged from 55 cm2/Vs to 220 cm2/Vs, and their carrier concentration was ∼1018 cm−3.