실리콘 기판위에 금속 완충층을 이용한 GaN 성장과 특성분석

Growth of high quality GaN layers with AlN buffer on Si(1 1 1) substrates

Stress generation and relaxation in AlN nucleation and buffer layers grown on c-Al2O3 substrates by plasma-assisted molecular beam epitaxy at low (LT, TS = 780°C) and high (HT, TS = 850°C) substrate temperatures were studied. Oscillation behavior of the wafer curvature (stress×thickness) was revealed during pulsed deposition of AlN in metal modulated epitaxy and migration enhanced epitaxy modes under the metal-rich conditions, which corresponded to Al bilayer formation and consumption. Minimal average stress ∼ +0.05 GPa in AlN buffer layers was observed at LT growth, which increased up to +0.85 GPa at HT growth. In addition, the LT AlN layers demonstrated lower densities of screw and edge threading dislocations equal to 7.8·108, 5.1·109 cm−2, respectively, while in the case of HT AlN layers those densities were significantly higher.

MOVPE of AlN-free hexagonal GaN/cubic SiC/Si heterostructures for vertical devices

We report the growth of high-quality GaN on a Si(111) substrate using a five step-graded AlxGa1−xN (x=0.87–0.07) interlayer between GaN epilayer and AlN buffer layer by ultrahigh vacuum chemical vapor deposition. The crack density and the surface roughness of the GaN layer grown on the graded AlxGa1−xN interlayer were substantially reduced, compared to those of GaN grown on an AlN buffer layer. Significant improvement in the structural and optical properties of the GaN layer was also achieved by the use of a graded interlayer. These results are attributed to the decrease of the lattice mismatch between GaN and AlN layer, and the reduction of the thermal stress by the graded interlayer.

To grow high quality a-GaN films on r-sapphire substrates, it is essential to optimize the buffer layers (BLs) growth parameters such as temperature, thickness, and V/III ratio. In this work, we investigated the effects of growth temperature for AlN BLs on the surface morphology and the crystal quality of a-GaN films. The films studied here were grown epitaxially by metalorganic chemical-vapor deposition (MOCVD) with different AlN BLs grown at 690 °C, 720 °C, 750 °C, respectively. The properties of a-GaN films were comprehensively studied via high resolution x-ray diffraction (HRXRD), optical microscope (OM) and atomic force microscope (AFM). It is found that the crystal quality and the surface morphology of a-GaN films have been remarkably affected by the growth temperature of the AlN BLs. At the optimum AlN BLs growth temperature of 720 °C, the a-GaN films have the best crystal quality – and the smoothest surface morphology with the (1120) HRXRD FWHM of 864 arcsec and the root mean square (RMS) surface roughness of 1.2 nm, respectively.

Growth and optical properties of GaN on Si(1 1 1) substrates

The annealing of an AlN buffer layer in a carbon-saturated N2–CO gas on a sapphire substrate was investigated. The crystal quality of the buffer layer was significantly improved by annealing at 1650–1700 °C. An AlN buffer layer with a thickness of 300 nm was grown by metalorganic vapor phase epitaxy (MOVPE), and was annealed at 1700 °C for 1 h. We fabricated a 2-µm-thick AlN layer on the annealed AlN buffer layer by MOVPE. The full widths at half maximum of the (0002)- and ()-plane X-ray rocking curves were 16 and 154 arcsec, respectively, and the threading dislocation density was 4.7 × 108 cm−2.

Wurtzite structure InN films were prepared on Si(100) substrates using radio‐frequency metal‐organic molecular beam epitaxy (RF‐MOMBE) system. Ga‐doped ZnO (GZO) and Amorphous AlN (a‐AlN) film were used as buffer layers for InN films growth. Structural, surface morphology and optical properties of InN films were investigated by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and photoluminescence (PL). XRD results indicated that all InN films exhibited preferred growth orientation along the c‐axis with different intermediate buffers. TEM images exhibit the InN/GZO growth by two‐dimensional mode and thickness about 900 nm. Also, the InN films can be obtained by growth rate about ~1.8 μm/h. Optical properties indicated that the band gap of InN/GZO is about 0.79 eV. These results indicate that the control of buffer layer is essential for engineering the growth of InN on silicon wafer.

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.

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Evolution of threading dislocations in MOCVD-grown GaN films on (1 1 1) Si substrates

ABSTRACTAlN films and GaN films with AlN buffer layers were deposited via metalorganic vapor phase epitaxy on Si(111) substrates previously exposed to trimethylaluminum for increasing times. Atomic force microscopy (AFM) was used to determine the influence of Al pre-flow time on the nucleation and surface morphology of the AlN and GaN films. When preceded by a 10 second Al pre-flow, AlN films feature an increased and more uniform nucleation density as compared to films deposited without Al pre-flows. Ten second Al pre-flows were also found to result in a reduction of the RMS roughness for 100 nm thick AlN films from 3.6 nm to 1.0 nm. AFM of 0.5 μm thick GaN films deposited on AlN buffers with varying pre-flow times showed reduced roughness and decreased pit density when using Al pre-flows of 10 or 20 seconds. High resolution x-ray diffraction of the GaN films showed a reduction in the average full-width halfmaximum (FWHM) of the GaN (00.2) reflection from 1076 arcsec to 914 arcsec when the AlN buffer layer was initiated with a 10 second Al pre-flow. Increasing the pre-flow time to 20 seconds and 30 seconds resulted in average (00.2) FWHM values of 925 arcsec and 928 arcsec, respectively. Similar behavior of the peak widths was observed for the (30.2) and (10.3) reflections when the pre-flow times were varied from 0 to 30 seconds.

In this article, the mechanical and deformation characteristics of epitaxial films of AlGaN solid solutions formed on silicon substrates of crystallographic orientations (001), (011) and (111) with a silicon carbide (SiC/Si) buffer layer synthesized by the method of the coordinated substitution of atoms were studied using the nanoindentation method. The growth of AlGaN epitaxial layers were carried out both directly on the SiC/Si hybrid substrate and on the SiC/Si substrate additionally coated with an AlN buffer layer. The morphology and structure of the surface of the layers was studied by atomic force microscopy. The structural characteristics of hybrid AlGaN substrates and films grown with and without an aluminum nitride buffer layer were measured. An unambiguous relationship has been established between the mechanical properties (elasticity modulus and hardness) and the surface structure of AlGaN films. It has been found that the AlN buffer layer has a significant effect on the mechanical and deformation properties of AlGaN films at the initial moment of indentation, when the layer is predominantly elastically deformed. The roughness was determined and the surface morphology of the AlGaN films was characterized. For the first time, experimentally, using the nanoindentation method, the hardness parameters and the reduced modulus of elasticity of epitaxial AlGaN grown on hybrid SiC/Si and AlN/SiC/Si substrates were measured.

Suppression of interfacial layer in high-K gate stack with crystalline high-K dielectric and AlN buffer layer structure

Deposition of GaN films on (111) Si substrates by alternate supply of TMG and NH3