Molecular Beam Epitaxy Growth Of GaN Research Articles

Plasma‐assisted MBE growth of GaN on Si(111) substrates

AbstractIn this work we present details of growth of GaN epitaxial layers on Si(111) substrates by molecular beam epitaxy (MBE) with the use of RF nitrogen plasma source. We focus on preparation of silicon substrate before the growth, on procedure of AlN buffer growth initiation (aluminum or nitrogen first) and on influence of III/N ratio on structural properties of the layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison of deep level incorporation in ammonia and rf‐plasma assisted molecular beam epitaxy n‐GaN films

AbstractThe use of rf‐plasma and ammonia nitrogen sources for growth of GaN films by molecular beam epitaxy (MBE) are compared in terms of defect incorporation using deep level optical spectroscopy (DLOS) and deep level transient spectroscopy (DLTS). To better improve the understanding of ammonia‐based MBE growth of GaN and potential defect sources as opposed to the more studied plasma source‐based MBE‐grown material several V/III ratios were also investigated, which were generated via systematic adjustment of the ammonia flow rates during growth. The DLOS spectra, comparing deep traps within the n‐GaN grown using N‐plasma and ammonia sources, reveal the presence of the same deep levels due to background carbon and gallium vacancies, with energy levels at EC‐3.28, EC‐2.62, and EC‐1.28. The DLTS results of the N‐plasma and ammonia‐based MBE samples show two similarly dominant electron traps at EC‐0.60, and EC‐0.24 in each sample. Measurements made as a function of V/III flux ratio for ammonia‐based MBE growth indicate a large dependence of the EC‐0.24 eV trap concentration on growth flux ratio, which is significant for guiding continued optimization of this promising MBE growth method for GaN devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Ga ion irradiation on growth of GaN on SiN substrates by electron cyclotron resonance-assisted molecular beam epitaxy

The possibility of forming GaN layers on Ga-implanted SiN surfaces was investigated using electron cyclotron resonance-assisted molecular beam epitaxy (MBE). It is found that the GaN layer initially formed on the SiN surface by Ga implantation at room temperature was amorphous-like, but become to polycrystalline after annealing at 650°C for 3min in vacuum. After the MBE growth of GaN, a grain structure of h-GaN was observed on the Ga-implanted SiN surface. The crystallinity of the GaN grown was, however, decreased upon increasing the Ga ion fluence on the SiN surface, which might be due, at least partly, to the formation of Ga clusters by the excess Ga implanted. The present results indicate the possibility of forming patterned GaN layers on SiN by selective Ga implantation on the SiN substrate, using a focused ion beam.

MBE growth of GaN on MgO substrate

We grow GaN on MgO substrate by plasma-assisted molecular beam epitaxy (MBE). It is revealed that hexagonal GaN grows on (1 1 1) MgO substrate and cubic GaN grows on (0 0 1) MgO substrate according to the symmetry of the substrates. Mixture of hexagonal phase into cubic GaN is found to be formed in the growth on (0 0 1) MgO, and is investigated by reciprocal space mapping. We obtained GaN epitaxial films with flat surface morphology and good crystalline quality on (1 1 1) MgO substrate.

GaN layers re-grown on etched GaN templates by plasma assisted molecular beam epitaxy

ABSTRACTThe growth of high-quality GaN by plasma assisted molecular beam epitaxy (MBE) is challenging, in part due to the constraint of heteroepitaxy since GaN substrates are not yet commercially available and isotropic nature of growth. Despite the large lattice and thermal mismatch between sapphire and GaN, the former is still the most commonly used substrate for the GaN-based optical devices at present. In this paper, we demonstrate a re-growth technique to obtain an improved quality GaN by MBE on GaN template on sapphire where the grossly defective regions have been removed. This GaN template is formed by MBE growth of GaN followed by wet chemical etching to selectively remove the defective region. Improved quality GaN was re-grown on such a template under Ga rich conditions to a thickness of about 1 micron. After re-growth, the surface of GaN is atomically smooth with spiral features in the short range. The low temperature PL of the re-grown GaN is superior to those of MBE GaN films directly on sapphire. Atomic force microscopy (AFM) images reveal a two-dimensional re-growth initiating in regions free of extended defects. The results show that the selectively etched GaN on sapphire can be used as a good template to improve the quality of GaN.

Effects of 6H-SiC surface reconstruction on lattice relaxation of AlN buffer layers in molecular-beam epitaxial growth of GaN

Growth of GaN on on-axis 6H-SiC (0001)Si substrates with an AlN buffer layer was performed by molecular-beam epitaxy. The effects of SiC surface reconstruction on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers were studied. High-temperature HCl-gas etching followed by HF chemical treatment resulted in an atomically flat SiC surface with a 1×1 structure. The AlN layer grown on the surface showed slow lattice relaxation. GaN grown on the AlN buffer layer exhibited the narrowest (0002) x-ray rocking curve of 70 arcsec and 107 cm−2 screw-type dislocation density, which was two orders of magnitude smaller than that of GaN grown on as-received substrates.

Delayed nucleation during molecular-beam epitaxial growth of GaN observed by line-of-sight quadrupole mass spectrometry

We present a nucleation study for molecular-beam epitaxial growth of GaN on 6H-SiC and sapphire using Rutherford backscattering, atomic force microscopy, and in situ line-of-sight quadrupole mass spectrometry. Film thickness measurements by Rutherford backscattering reveal a strong deviation from thickness calculations assuming steady-state growth. We differentiate two regimes of growth, initially a highly nonlinear growth mode during island formation and later a linear growth mode after coalescence of islands. The mechanisms leading to the nonlinear behavior are attributed to energy barriers that supress immediate nucleation and provide for a substantial desorption of Ga and N atoms. Employing line-of-sight quadrupole mass spectrometry, we developed a quantitative in situ method to determine the amount of desorbing Ga atoms during the entire GaN growth procedure. The amount of initial GaN desorption in heteroepitaxy is independent of the substrate material and is as high as 8±1.5 nm.

In as a surfactant for the growth of GaN (0001) by plasma-assisted molecular-beam epitaxy

The influence of indium on the surface morphology of GaN (0001) grown by plasma-assisted molecular-beam epitaxy (MBE) has been investigated. The rough and grain-like surface under nitrogen-rich growth conditions becomes smoother and similar to surfaces grown under gallium-rich conditions when a sufficiently high indium flux is used. However, the use of indium instead of gallium-rich conditions prevents the formation of gallium droplets on the surface which are associated with voids at their edges. Since indium is not incorporated into GaN for growth temperatures above 700 °C, it can be used as a surfactant in MBE growth of GaN.

Initial stages of molecular-beam epitaxy growth of GaN on 6H-SiC(0001)

We studied the atomic H etching of 6H-SiC substrates and the initial stages of GaN/6H-SiC molecular-beam epitaxy growth. Atomic H etched 6H-SiC(0001)Si and (0001̄)C surfaces show a (∛×∛)−R30° and a (1×1) reconstruction respectively, with 0.7±0.2 monolayers of remnant O on both surfaces. GaN/6H-SiC(0001)Si growth is initiated by the formation of islands that develop into flat-top terraces through coalescence. Growth steps of one or integer numbers of the GaN atomic bilayer height are observed. GaN grown on 6H-SiC(0001̄)C is rougher with islands of irregular shape. X-ray photoemission spectroscopy studies show that Si 2p and C 1s photoelectron inelastic mean free paths in GaN are 22±1 and 20±1 Å, respectively.

Problems and prospects in the analysis of epitaxial growth of the wide bandgap Group-III nitrides

A review of the experimental situation in molecular-beam epitaxial growth of GaN is given in the framework of three problem areas that may be susceptible to computational methods: relaxation of strain in large mismatch systems, growth-surface kinetics of plasma-excited nitrogen, and surfactant-mediated epitaxy. Basic properties of acceptor-doped GaN are discussed and then the importance of these three problem areas is made clear via examination of recent experimental results.