Epitaxial Growth Of AlN Research Articles

Образование полуполярных III-нитридных слоев на поверхности Si(100), структурированной с помощью самоформирующейся наномаски

The epitaxial growth of AlN and GaN layers was studied by Metalorganic Vapor Phase Epitaxy, on a Si(100) substrate, on the surface of which a V-shaped nanostructure with sub-100 nm element size (NP-Si(100)) was formed. It is shown that a corrugated surface is formed from semipolar AlN(10-11) planes with opposite "c"axes during the formation of a semipolar AlN layer at the initial stage of epitaxy. Then, during the growth of the GaN layer, the transition from the symmetric state of two semipolar AlN planes to an asymmetric state with a single orientation of the "c"-axis of the semipolar GaN(10-11) layer occurs, and the "c" direction in the growing semipolar layer coincides with the direction of the flow of N2+ ions to the silicon surface during the formation of a nanomask.

Microstructural analysis in the depth direction of a heteroepitaxial AlN thick film grown on a trench-patterned template by nanobeam X-ray diffraction

This work quantitatively assessed the three-dimensional distribution of crystal lattice distortions in an epitaxial AlN thick film grown on a trench-patterned template, using nanobeam X-ray diffraction. Position-dependent ω-2θ-φ mapping clearly demonstrated local tilting, spacing and twisting of lattice planes as well as fluctuations in these phenomena on a sub-micrometer scale comparable to the pitch of the trench-and-terrace patterning. Analysis of the crystal lattice distortion in the depth direction was performed using a newly developed method in which the X-ray nanobeam diffracted from the sample surface to specific depths can be selectively detected by employing a Pt wire profiler. This technique generated depth-resolved ω-2θ-φ maps confirming that fluctuations in lattice plane tilting and spacing greatly depend on the dislocation distribution and the history of the AlN epitaxial growth on the trench-patterned structure. It was also found that both fluctuations were reduced on approaching the AlN surface and, in particular, were sharply reduced at specific depths in the terrace regions. These sharp reductions are attributed to the formation of sacrificial zones with degraded crystal quality around the trenches and possibly lead to raising the crystal quality near the surface of the AlN film.

Epitaxial Growth of AlN on (0001) Sapphire: Assessment of HVPE Process by a Design of Experiments Approach

This study aims to present the interest of using a design of experiments (DOE) approach for assessing, understanding and improving the hydride vapor phase epitaxy (HVPE) process, a particular class of chemical vapor deposition (CVD) process. The case of the HVPE epitaxial growth of AlN on (0001) sapphire will illustrate this approach. The study proposes the assessment of the influence of 15 process parameters on the quality or desired properties of the grown layers measured by 9 responses. The general method used is a screening design with the Hadamard matrix of order 16. For the first time in the growth of AlN by CVD, a reliable estimation of errors is proposed on the measured responses. This study demonstrates that uncontrolled release of condensed species from the cold wall is the main drawback of this process, explaining many properties of the grown layers that could be mistakenly attributed to other phenomena without the use of a DOE. It appears also that the size of nucleation islands, and its corollary, the stress state of the layer at room temperature, are key points. They are strongly correlated to the crystal quality. Due to the intrinsic limitations of the screening design, the complete optimization of responses cannot be proposed but general guidelines for hydride (or halogen) vapor phase epitaxy (HVPE) experimentations, in particular with cold wall apparatus, are given.

CFD modeling of the high-temperature HVPE growth of aluminum nitride layers on c-plane sapphire: from theoretical chemistry to process evaluation

This study presents numerical modeling based on a relatively limited number of gas-phase and surface reactions to simulate the growth rate of aluminum nitride layers on AlN templates and c-plane sapphire in a broad range of deposition parameters. Modeling results have been used to design particular experiments in order to understand the influence of the process parameters on the crystal quality of AlN layers grown in a high-temperature hydride vapor-phase epitaxy process fed with NH3, AlCl3, and H2. Modeling results allow to access to very interesting local quantities such as the surface site ratio and local supersaturation. The developed universal model starting from local parameters might be easily transferred to other reactor geometry and process conditions. Among the investigated parameters (growth rate, temperature, local supersaturation, gas-phase N/Al ratio, and local surface site N/Al ratio), only the growth rate/supersaturation or growth rate/temperature relationships exhibit a clear process window to use in order to succeed in growing epitaxial AlN layers on c-plane sapphire or AlN templates. Gas-phase N/Al ratio and local surface site N/Al ratio seem to play only a secondary role in AlN epitaxial growth.

Effect of dual buffer layer structure on the epitaxial growth of AlN on sapphire

A dual AlN buffer layer structure, including an isolated layer and a nucleation layer, is proposed to improve the growth of AlN films on sapphire substrate by metal organic chemical vapor deposition. This method is aimed to weaken the negative nitridation effect and improve lateral growth condition in the initial growth stage. It is found that suitably increasing the thickness of the nucleation layer is in favor of a better structural quality of the AlN film. An examination of surface morphology by atomic force microscopy suggests that the thicker the dual AlN buffer layer, the rougher the surface, and a higher quality of AlN epilayer is resulted.

Investigation on AlN epitaxial growth and related etching phenomenon at high temperature using high temperature chemical vapor deposition process

Thick AlN layers were grown by high temperature chemical vapor deposition (HTCVD) on 8° off-axis (0 0 0 1) 4H-SiC, on-axis (0 0 0 1) 6H-SiC and on-axis (0 0 0 1) AlN templates between 900 °C and 1600 °C. The experimental set-up consists of a vertical cold-wall reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH 3) and aluminum chlorides (AlCl x ) species in situ formed via Cl 2 reaction with high purity aluminum wire. As-grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Optical Profilometry, Atomic Force Microscopy (AFM) and Raman spectroscopy. In this study, the influence of the deposition temperature and the N/Al ratio in the gas phase is studied in order to stabilize epitaxial growth. The epitaxy on AlN template is favored using a low N/Al ratio in the gas phase and a high temperature above 1400 °C. The crystalline quality of epitaxial AlN layers is found to increase with increasing deposition temperature from 1400 to 1500 °C. Growth rates up to 14 μm h −1 have been reached for epitaxial AlN layers. An important etching phenomenon is also observed at high temperature: apparition of pin holes certainly around threading dislocations at 1400–1500 °C and substrate etching at 1600 °C.

Emergence of (001) preferred orientation in AlN film using ultrathin intermediate Pt layer

<title/>The preferred orientations of AlN films with an intermediate Pt layer have been examined using X-ray diffraction and transmission electron microscopy. It is found that the Pt layer encourages the AlN film into c axis preferred orientation deposition, even though the sputtering conditions would normally lead the AlN film to be deposited with other preferred orientations. The Pt layer also promotes the crystallisation of AlN films. The local epitaxial growth of AlN (001) on Pt (111) may elucidate the effect of the Pt layer on the preferred orientation control.

HRTEM Analysis of AlN Layer Grown on 3C-SiC/Si Heteroepitaxial Substrates with Various Surface Orientations

Epitaxial growth of AlN was carried out by MOVPE method on SiC/Si buffered substrates prepared by using various Si surfaces of (110), (211) and (001). Cross-sectional HRTEM analyses of the interfaces between SiC buffer layer and AlN epitaxial layer disclosed characteristic nanostructures related growth mechanism on the each substrate. In the case of Si(110) and Si(211) substrate, hexagonal AlN grew directly on SiC(111) plane with AlN(0001) plane parallel to it. In contrast, growth on Si(001) substrate gave complicate structure at AlN/SiC interface. Hexagonal AlN didn’t grow directly but cubic AlN appeared with a pyramidal shape on SiC(001). When the cubic AlN grew 10nm in height, structure of growing AlN crystal changed to hexagonal type on the pyramidal {111} planes of cubic AlN.

Epitaxial growth of aluminum nitride on AlGaN by reactive sputtering at low temperature

We report the synthesis of 1μm thick single crystalline aluminum nitride films by dc magnetron sputtering on AlGaN∕GaN layer grown on sapphire substrate at low temperature (substrate temperature &amp;lt;250°C). The microstructure of c-axis oriented AlN films deposited on Si (100) and AlGaN ⟨0001⟩ substrates was studied by x-ray diffraction, selected area electron diffraction, and transmission electron microscopy. The optimization of process parameters, involving low energetic ion bombardment on film surface (20–30eV) during the growth, leads to an increase in the surface mobility and thus promotes AlN epitaxial growth on AlGaN substrate at 250°C.

Epitaxial growth of AlN on Cu(1 1 1) substrates using pulsed laser deposition

We have succeeded in the epitaxial growth of AlN on Cu(1 1 1) substrates using pulsed laser deposition (PLD) for the first time. We achieved atomically flat surfaces of Cu(1 1 1) by annealing in an ultra high vacuum chamber. In situ X-ray photoelectron spectroscopy and reflection high-energy electron diffraction studies revealed that the native oxide layers on the surfaces had been successfully removed and that the Cu surfaces were reformed by the segregation of antimony atoms, incorporated in the substrates as impurities. We found that AlN (0 0 0 1) grows epitaxially on Cu(1 1 1) at a substrate temperature of as low as 500 °C with in-plane epitaxial relationships of AlN [ 11 2 ¯ 0 ] / / Cu [ 1 1 ¯ 0 ] . Electron backscattering diffraction measurements showed that neither 30° rotational domains nor cubic phase domains exist in the AlN films. Spectroscopic ellipsometry measurements revealed that no interfacial layers exist at the AlN/Cu hetero interfaces within the limits of detection. These results indicate that the PLD low-temperature growth technique permits the preparation of high-quality AlN expitaxial films on single-crystal metal substrates.

Growth of high‐quality non‐polar AlN on 4H‐SiC(11–20) substrate by molecular‐beam epitaxy

Non-polar AlN epitaxial growth on SiC substrates with the (11–20) face, which is parallel to the 〈0001〉 direction, has been investigated. AlN(11–20) epilayers were grown on 6H- and 4H-SiC(11–20) substrates by molecular-beam epitaxy (MBE) using elemental Al and rf plasma-excited nitrogen. The crystalline structure of the AlN layer was strongly influenced by the stacking structure of the SiC substrate. A considerably smooth AlN(11–20) layer with an rms roughness of 0.3 nm was obtained on the 4H-SiC(11–20) substrate. From the results of X-ray diffraction (XRD), the superior crystalline quality of the AlN(11–20) layer on the 4H-SiC(11–20) substrate was clearly shown.

Structural properties and Raman measurement of AlN films grown on Si (1 1 1) by NH 3-GSMBE

Epitaxial growth of AlN has been performed by molecular beam epitaxy (MBE) with ammonia. The structural properties of materials were studied by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). XRD and TEM diffraction pattern confirm the AlN is single crystalline 2H-polytype with the epitaxial relationship of (0 0 0 1)AlN∥(1 1 1)Si, [1 1 2 ̄ 0] AlN ∥[1 1 0] Si, [1 0 1 ̄ 0] AlN ∥ [1 1 2 ̄ ] Si . Micro-Raman scattering measurement shows that the E 2 (high) and A 1 (LO) phonon mode shift 9 cm −1 toward the low frequency, which shows the existence of large tensile strain in the AlN films. Furthermore, the appearance of forbidden A 1 (TO) mode and its anomalous shift toward high frequency was found and explained.

Epitaxial growth of AlN on sapphire (0 0 0 1) by sputtering: a structural, morphological and optical study

We report on the growth conditions dependence of the morphology and structural quality of epitaxial AlN thin films deposited by normal incidence reactive sputtering. The crystallographic quality is increased for higher concentrations of nitrogen in the plasma during the deposition process. Also the presence of an intermediate AlN buffer is found to reduce the stress induced by the substrate and to enhance the quality of the subsequent AlN deposit; the morphology and roughness of the surface of the deposit depend on the deposition temperature of the buffer layer. From spectroscopic ellipsometry measurements we deduce and present the evolution of the refractive index and extinction coefficient with the wavelength for AlN deposits obtained under different growth conditions.

Studies on Epitaxial Relationship and Interface Structure of AlN/Si(111) and GaN/Si(111) Heterostructures

ABSTRACTWe present the details of epitaxial growth interface structure of single wurtzite AlN thin films on (111) Si substrates by laser-molecular-beam-epitaxy. High quality AlN thin films with atomically sharp interfaces can be obtained by Laser-MBE at a substrate temperature of 650 ±10°C. X-ray diffraction and high resolution transmission electron microscopy was used to study the details of epitaxial growth of AlN on Si(111) substrate. The orientation-relationship of AlN on Si(111) was studied from Si &lt;110&gt; and &lt;112&gt; zone axis and determined to be AlN [2110]|Si[110] and AlN [0110]|Si[211]. The atomic structure of the interface was studied by high-resolution transmission electron microscopy and Fourier filtered image of cross-sectional AlN/Si(111) samples from both Si&lt;110&gt; and &lt;112&gt; zone axis. The results revealed the domain matching epitaxy of 4:5 ratio between the interplanar distances of Si(110) and AlN [2110]. We also present similarities and differences between the growth mechanism of AlN/Si(111) and GaN/Si(111) heterostructures.

AlN epitaxial growth on off-angle R-plane sapphire substrates by MOCVD

A-plane (1 2 ̄ 1 0) AlN films were deposited on the off-angle R-plane (1 1 ̄ 0 2) sapphire substrates, in which the surface plane was tilted towards the [1 1 ̄ 01] sapphire direction, by metalorganic chemical vapor deposition in order to clarify off-angle effects. The polar direction of the AlN film was inverted by changing the sign of the off-angle and the off-angle was effective in restraining the generation of inverted twins in the AlN. A minus off-angle was found to improve total crystal quality of the AlN from X-ray diffraction results. High-resolution transmission electron microscopy images in the vicinity of interfaces between the AlN and the sapphire indicated that atomic arrangement at an initial AlN growth stage influenced the total crystal quality.

RHEED monitoring of AlN epitaxial growth by plasma-assisted molecular beam epitaxy

We have studied the epitaxial growth of AlN layers by plasma-assisted molecular beam epitaxy (MBE) on 6H–SiC substrate. Reflection high-energy electron diffraction (RHEED) was used to monitor the growth by the observation of the 2D–3D growth transition, respectively, in Al- and N-rich conditions. Special attention was given to the elimination of the Al droplets which often form in Al-rich conditions. Different growth procedures are proposed to avoid the appearance of these droplets while keeping a 2D growth. Each of the procedure gives AlN epilayers with identical crystalline quality and low surface roughness as measured, respectively, by X-ray diffraction and atomic force microscopy.

Interface Characterization of AlN/TiN/MgO(001) Prepared by Molecular Beam Epitaxy

The AlN/TiN/MgO(001) interfaces, prepared by molecular beam epitaxy, have been characterized by cross-sectional high-resolution electron microscopy (HREM). The thin TiN buffer layer, with the thickness of 40 nm, is epitaxially grown on the MgO(001) substrate. Owing to the same structure-type as well as the small mismatch of their lattice parameters, the growth is governed by the parallel orientation relationship of (001)TiN||(001)MgO, (010)TiN||(010)MgO, and (111)TiN||(111)MgO. Two kinds of processes of the hexagonal AlN epitaxial growth on the as-received TiN(001), differed by the (0001)AlN plane parallel to, and the (1012) plane approximately parallel to the MgO substrate surface, respectively, are identified, and within them, several cases are classified which are based on the consideration of crystallographic symmetry. Theoretical calculations based on the geometrical model that was recently proposed and applied to a number of epitaxial systems have been carried out to rationalize these observations.

Epitaxial Growth of AlN on Si Substrates with Intermediate 3C-SiC as Buffer Layers

ABSTRACTSingle crystalline AlN was successfully grown on a 3C-SiC coated Si (111) substrate by organometallic vapor phase epitaxy. The 3C-SiC film was obtained via the conversion of the Si near-surface region to SiC using gas-source molecular beam epitaxy. The quality of the AlN was mainly controlled by that of the SiC. The effects of Si pits and SiC hillocks formed during the conversion on subsequent AlN growth are discussed. Process optimization is suggested to improve the SiC buffer layer for subsequent AlN deposition.

Epitaxial Growth of III-Nitride Layers on Aluminum Nitride Substrates

High quality, epitaxial growth of AlN and AlxGa1−xN by OMVPE has been demonstrated on single-crystal AlN substrates. Here we report characterization of epitaxial layers on an a-face AlN substrate using Rutherford Backscattering/ion channeling, atomic force microscopy (AFM), x-ray rocking curves, and preliminary electrical characterization. Ion channeling along the [100] axis gives a channeling minimum yield of 1.5% indicating a very high quality epitaxial layer.

MBE Growth and Ultrahigh Temperature Processing of High-Quality AlN Films

AbstractMolecular beam epitaxial growth of AlN on sapphire and 6H-SiC has been performed utilizing mono-energetic activated nitrogen ion beams (2-80 eV kinetic energies). The growth temperature of AlN in MBE is found to be limited by the sticking coefficient of incident reactants. The combination of elevated growth temperatures (1050-1150°C), high kinetic-energy reactive nitrogen (&gt;40 eV) and post-growth thermal processing (1150-1350°C) produces high-quality AlN thin-f ilms with narrow rocking curve widths (&lt;2 arcmin) and low dislocation densities (&lt;∼3×108cm−2). In contrast, the use of in-situ step anneals during synthesis did not achieve similar quality materials.