Growth Of InN Research Articles

A trade‐off relation between tilt and twist angle fluctuations in InN grown by RF‐MBE

AbstractIn the InN growth on sapphire substrates, it is difficult to control both of tilt and twist angle fluctuations at same time. It is necessary to understand initial growth stage such as the role of nitridation process to improve the mosaicity. Low‐temperature nitridation technique brings the drastically improvement of the tilt angle fluctuation, although the twist angle fluctuation becomes worse. Such experimental results strongly indicate that there is some trade‐off relation between the tilt and the twist angle fluctuations as a function of the nitridation condition such as the nitridation time. In this paper, we discuss about such trade‐off relation in the direct growth of InN on the nitridation sapphire substrates and also propose a simple model of initial nitridation process to explain it. (© 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)

InN Growth by Plasma-Assisted Molecular Beam Epitaxy with Indium Monolayer Insertion

An etching effect of N-plasma on a GaN buffer layer was found in the initial stage of InN growth by plasma-assisted molecular beam epitaxy. We proposed to predeposit 1–2 monolayers (ML) of In (referred to as “In insertion”) on the GaN buffer layer to protect it from etching, thus preserving the flat buffer surface for InN growth. Atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) were carried out to evaluate the GaN buffers and InN films and compare the effect of the In insertion. It has been shown that the In insertion significantly improves the structural quality and optical property of InN. A flatter InN surface, narrower XRD full-width at half-maximum, sharper InN/GaN interface, and stronger PL were observed in optimal samples with 1.8 ML In insertion. The effect of In insertion is discussed in terms of buffer surface protection and enhancement of surface migration of In adatoms.

Mg doping of InN and the use of yttrium‐stabilised zirconia substrates

AbstractDetermining fundamental properties of InN is beset with difficulties. Since a conducting surface accumulation layer creates difficulties when assessing the impact of dopants, variable magnetic field Hall effect measurements were performed to separate various conducting layers. In addition to verifying p‐type doping with Mg, variable magnetic field Hall effect was used to show that growth of InN on YSZ will greatly reduce the background n‐type concentration for thinner layers, (with n ∼ 2×1017 cm−3, the lowest achieved on half micron thick material), making microns‐thick growth less important than the typical method of growth on sapphire with GaN buffer layers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Influence of hydrogen input partial pressure on the polarity of InN on GaAs (111)A grown by metalorganic vapor phase epitaxy

Influences of hydrogen input partial pressure in the carrier gas ( F o = P H 2 o / ( P H 2 o + P N 2 o ) ) on the crystalline quality and polarities of InN on GaAs (1 1 1)A surfaces were investigated by metalorganic vapor phase epitaxy (MOVPE). It was found that the polarity of the InN was affected by the hydrogen gas in the system regardless of the polarity of GaAs starting substrate. The polarity of InN layer grown with the hydrogen partial pressure of F o =0.004 was a mixture of In-polarity and N-polarity, while that grown with F o =0 was In-polarity. Degradation of the crystalline quality of InN grown with F o =0.004 occurred due to the polarity inversion during the growth. The reason why the polarity of InN was influenced by the hydrogen carrier gas could be explained by the preferential growth of N-polarity InN in the H 2 contained ambient and/or the limiting reaction of InN decomposition.

Growth of InN by Plasma-Assisted Molecular Beam Epitaxy on InN/GaN and p-GaN Templates

InN is grown by plasma-assisted molecular beam epitaxy on templates prepared by hydride vapor phase epitaxy. These uniques templates consist of InN/GaN and p-GaN epilayers. Homoepitaxy creates challenges for surface preparation prior to growth. Quality InN layers as seen by x-ray diffraction and photoluminescence data are developed when growing on HVPE InN/GaN templates. InN growth on p-GaN provides a novel solution for p-down diodes utilizing InN. The in situ surface preparation of these templates is a challenge preventing undesirable band bending at the hetero-interface. Two in situ surface preparations are attempted with no significant impact on the quality of the InN layer.

Growth of InN by Plasma-Assisted Molecular Beam Epitaxy on InN and p-GaN Templates

not Available.

Piezoelectric coefficient of InN films prepared by radio-frequency sputtering

An interferometric method has been used to measure the piezoelectric coefficient d 33 in indium nitride films deposited by radio-frequency sputtering on borosilicate glass coated with gold. This low temperature growth technique has the advantage of being able to produce samples for piezoelectric measurements where the InN film is grown directly on an Au metal back contact, allowing the accurate measurement of the piezoelectric coefficient of the InN layer without any parasitic series resistance. The InN growth conditions are described, and both crystal and optical characterizations of the film are presented. The measured value of the coefficient was found to be 4.0 ± 0.1 pm V − 1 .

MOCVD growth of InN using a GaN buffer

We have investigated MOCVD growth of InN on sapphire with and without a GaN buffer between 490 and 520 ∘C. The buffer significantly improves the surface morphological uniformity and electrical properties of InN epilayers. Characterization of the as-grown epilayers with the buffer reveals that kinetics-limited islands are formed at lower temperatures, whereas islands with equilibrium shape are obtained at higher temperatures. Below 520 ∘C, increasing temperature improves structural quality but degrades electrical properties. Hall data from this study suggest that V N -related defects/impurities are the possible donor species and compensation varies with charged dislocation acceptors. We believe that reducing carrier concentration and dislocation density is effective to increase the Hall mobility of InN.

Polarity control of InN grown by MOVPE on sapphire (0001)

Polarity control of MOVPE InN on sapphire (0001) was investigated. Two kinds of polarity InN films on sapphire substrate by MOVPE have been prepared by controlling the substrate nitridation process and/or the LT-GaN buffer annealing process. Surface of the nitrided sapphire is a crucial factor in determining the polarity of InN film. N-polarity InN film was grown on the 1000 °C-nitrided substrate without LT-GaN buffer; while In-polarity InN film was grown on the 900 °C-nitrided substrate. In the case of InN growth with a LT-GaN buffer, buffer annealing is a crucial issue in determining the polarity of InN film. N- and In-polarity InN films were obtained on the long-time-annealed buffer and the short-time-annealed buffer, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Real time optical monitoring of molecular beam epitaxy of InN on SiC substrates

Spectroscopic ellipsometry has been used to monitor in real time and in situ the molecular beam epitaxial growth of InN on SiC substrates. A three-step growth process consisting of (i) low-temperature (200°C) nitridation of the SiC surface, (ii) low-temperature (350°C) nucleation of a thin InN buffer layer, and (iii) growth of the InN epitaxial layer at 450°C has been applied. The impact of the In flux on the growth kinetics, morphology, and structural and optical properties of InN has been investigated. It is found that independent of the In flux the low-temperature buffer shows In surface accumulation. This In surface accumulation increases during InN growth under In-rich conditions and is depleted during growth under intermediate and N-rich conditions. Better structural, morphological, and optical properties are obtained when the films are grown under In-rich conditions.

Initial stages of the cubic-InN growth with the technique of the pre-deposition of indium

The initial stages of the cubic indium nitride film growth at 350 °C were studied using low-pressure metal-organic chemical vapor deposition. The technique of the pre-deposition of indium was applied, that is, a layer of indium was first deposited on sapphire surface before the growth of InN. X-ray diffraction and X-ray photoelectron spectroscopy show that the pre-deposition of indium is able to promote the growth of InN films, and meanwhile, suppress the indium aggregation in the as-grown films. Atomic force microscopy images of InN films indicate that the pre-deposition of indium not only enhances the density of nucleate sites, but also facilitates the coalescence among the InN islands. The free energy calculations reveal that the pre-deposited indium atoms preferentially react with NH and N radicals after NH3 introduction, which leads to the formation of InN on the sapphire surface. The preferentially formed InN is then supposed to be responsible for the above phenomena.

RF–MBE growth and structural characterization of cubic InN films on yttria-stabilized zirconia (0 0 1) substrates

Cubic InN (zincblende structure) films have been successfully grown on yttria stabilized zirconia (YSZ) (0 0 1) substrates by RF-plasma-assisted molecular beam epitaxy. The X-ray diffraction analysis has confirmed the growth of cubic InN films whose growth temperature was 400– 490 ∘ C and crystal quality is higher than that on GaAs (0 0 1) substrate. The structural properties (i.e. crystal quality and cubic phase purity) of the InN films are obviously improved for the growth condition of a slightly In-rich side of the surface-stoichiometry. By 2 θ / ω and ω X-ray reciprocal space mapping measurements, hexagonal phase InN (h-InN) is found to be generated from c- InN { 1 1 1 } facets. By annealing at several temperatures in air, the surface morphology of YSZ substrates remarkably changes and appears as the stepped and terraced structure. With increasing annealing temperature, the step wandering disappears and the step edges become straighter. By using YSZ substrate with stepped and terraced structure for cubic InN growth, the volume content of cubic InN is drastically increased and is estimated to be ∼ 95 % at maximum based on an analysis of the X-ray diffraction intensity.

Blue and green emission using In(Ga)N/GaN quantum wells with InN well layers grown by metalorganic chemical vapor deposition

In(Ga)N/GaN multiple quantum well structures with high indium composition were grown using pure InN in well layers by low-pressure metalorganic chemical vapor deposition. Blue emission using a thin In(Ga)N well width grown with only trimethylindium as a III-source showed strong carrier localization originating from a large fluctuation in indium composition and a reduced quantum-confined Stark effect due to the use of a thin well, both of which enhanced quantum efficiency. In contrast, an increase in InN growth time to achieve green emission exhibited a large blueshift of electroluminescent emission under forward-bias current and microstructural defect formation, which were responsible for the observed degradation in emission properties.

The influence of indium monolayer insertion on the InN epifilm grown by plasma-assisted molecular beam epitaxy

InN films were grown on GaN buffer layer by plasma-assisted molecular beam epitaxy (PA-MBE). We found that an In layer insertion between GaN buffer and InN film significantly improves the crystal quality and optical property of InN. The comparison of the GaN buffers with different treatment indicates that GaN buffer without In deposition is easily etched by N plasma when InN growth starts, and a 1–2 monolayers (ML) In can effectively prevent GaN from etching, thus maintaining the flat buffer surface for InN growth. With the optimum coverage of In insertion of 1.8 ML, the subsequent InN epifilm shows an atomically flat surface with root-mean-square (RMS) roughness as low as 0.2 nm. The peak intensity of photoluminescence (PL) from the same sample is increased by a factor of ∼20 compared with the InN film grown without In insertion.

Initial growth stages of MOVPE InN studied by AFM and specular reflectivity

The initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X-ray specular reflectivity for five different thin films ranging from 57 to 750 Å. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two-dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 Å the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-temperature MOCVD growth of InN buffer layers with indium pre-deposition technology

Cubic-InN was grown at a low temperature of 350 °C using our home-made low-pressure metal-organic chemical vapor deposition (MOCVD). The technology of indium pre-deposition was applied, that is, a layer of indium was deposited on the sapphire surface with a precursor of trimethylindium (TMI) before the growth of InN. Both X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectra show that the pre-deposited indium is able to promote the growth of InN, and meanwhile, suppress the indium aggregation in the grown layer. Atomic force microscopy (AFM) images indicate that the nucleation of InN becomes easier with the pre-deposition of indium. It is proposed that the pre-deposited indium can seed the growth of InN, just like the vapor–liquid–solid (VLS) fabrication of InN whiskers with indium nanoparticles.

Hydride vapor phase epitaxy of InN by the formation of InCl 3 using In metal and Cl 2

Hydride vapor phase epitaxy (HVPE) of InN using In metal, Cl 2 and NH 3 as source materials and N 2 carrier gas was investigated on sapphire (0 0 0 1) substrates. A thermodynamic analysis of the reaction between In metal and Cl 2 gas in the source zone of the HVPE system revealed that the equilibrium partial pressure of InCl 3 increased significantly with decreasing source zone temperature, while that of InCl remained almost constant. At a substrate temperature of 500 °C, appreciable growth of InN occurred by decreasing the source zone temperature to 450 °C. This means that InN growth occurs by the reaction between InCl 3 and NH 3. With an optimum surface nitridation time of the sapphire substrate prior to InN growth, c-axis oriented single-crystalline layers of InN were obtained. Cathodoluminescence (CL) spectrum measured at room temperature showed a strong peak at 0.75 eV.

Electrical and optical properties of MOVPE InN doped with Mg using CP 2Mg

The first trial of Mg doping in the atmospheric-pressure MOVPE growth of InN has been made using CP 2Mg as a Mg source. Although Mg is incorporated in the InN films and its content is proportional to CP 2Mg/TMI molar ratio, all samples grown here show n-type conduction and the electron concentration is rather increased with increasing CP 2Mg/TMI molar ratio. The SIMS analysis reveals that C and H are also incorporated into the grown films. The AFM observation shows that the grain growth of InN is suppressed by the CP 2Mg supply. Both the contamination of C and H and the effect of the CP 2Mg supply to the grain growth are considerably reduced by selecting the substrate position on the susceptor.