skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates

Abstract

A series of m-plane GaN layers with the Ga beam-equivalent pressure (BEP) as the only varied parameter was grown by rf-plasma assisted molecular beam epitaxy on m-plane 4H-SiC substrates using AlN buffer layers. The smoothest growth surfaces and most complete film coalescence were found for the highest Ga BEP corresponding to the Ga droplet accumulation regime. However, better structural quality as assessed by x-ray rocking curves was observed for growth at a lower Ga BEP value below the droplet limit. The variation of rocking curve widths for planes inclined with respect to the epilayer c axis followed a different trend with Ga BEP than those of reflections parallel to the c axis. The GaN layers were found to exhibit a large residual compressive strain along the a axis.

Authors:
; ; ;  [1]
  1. Department of Electronics Science and Engineering, Kyoto University, Kyo-dai Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
Publication Date:
OSTI Identifier:
20982675
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 3; Other Information: DOI: 10.1063/1.2435806; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM NITRIDES; BUFFERS; COALESCENCE; CRYSTAL GROWTH; DROPLETS; GALLIUM NITRIDES; LAYERS; MOLECULAR BEAM EPITAXY; NEUTRON DIFFRACTION; PLASMA; RESIDUAL STRESSES; SEMICONDUCTOR MATERIALS; SUBSTRATES; THIN FILMS; X-RAY DIFFRACTION

Citation Formats

Armitage, R., Horita, M., Suda, J., and Kimoto, T.. m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates. United States: N. p., 2007. Web. doi:10.1063/1.2435806.
Armitage, R., Horita, M., Suda, J., & Kimoto, T.. m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates. United States. doi:10.1063/1.2435806.
Armitage, R., Horita, M., Suda, J., and Kimoto, T.. Thu . "m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates". United States. doi:10.1063/1.2435806.
@article{osti_20982675,
title = {m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates},
author = {Armitage, R. and Horita, M. and Suda, J. and Kimoto, T.},
abstractNote = {A series of m-plane GaN layers with the Ga beam-equivalent pressure (BEP) as the only varied parameter was grown by rf-plasma assisted molecular beam epitaxy on m-plane 4H-SiC substrates using AlN buffer layers. The smoothest growth surfaces and most complete film coalescence were found for the highest Ga BEP corresponding to the Ga droplet accumulation regime. However, better structural quality as assessed by x-ray rocking curves was observed for growth at a lower Ga BEP value below the droplet limit. The variation of rocking curve widths for planes inclined with respect to the epilayer c axis followed a different trend with Ga BEP than those of reflections parallel to the c axis. The GaN layers were found to exhibit a large residual compressive strain along the a axis.},
doi = {10.1063/1.2435806},
journal = {Journal of Applied Physics},
number = 3,
volume = 101,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • In-plane anisotropic lattice relaxation was correlated with the crystal mosaicity and luminescence spectra for m-plane Al{sub x}Ga{sub 1-x}N films grown on a freestanding GaN substrate by NH{sub 3}-source molecular beam epitaxy. The homoepitaxial GaN film exhibited A- and B-excitonic emissions at 8 K, which obeyed the polarization selection rules. For Al{sub x}Ga{sub 1-x}N overlayers, the m-plane tilt mosaic along c-axis was the same as the substrate as far as coherent growth was maintained (x{<=}0.25). However, it became more severe than along the a-axis for lattice-relaxed films (x{>=}0.52). The results are explained in terms of anisotropic lattice and thermal mismatches betweenmore » the film and the substrate. Nonetheless, all the Al{sub x}Ga{sub 1-x}N films exhibited a near-band-edge emission peak and considerably weak deep emission at room temperature.« less
  • We study the properties of (Al,In)N layers and (Al,In)N/GaN heterostructures grown on 6H-SiC(0001) by plasma-assisted molecular beam epitaxy. The (Al,In)N films are deposited on a GaN buffer layer. A growth temperature of 500 deg. C and above results in low In contents which give rise to cracks due to the large tensile strain experienced from the underlying GaN buffer layer. In addition, these layers exhibit strong phase separation leading to inhomogeneous In composition and rough surfaces. In contrast, samples with homogeneous and well-controlled In-contents between 10%-30% are reproducibly obtained in the temperature range of 250-350 deg. C. Surprisingly, nominally lattice-matchedmore » layers with an In content of 17%-18% also exhibit cracks. Symmetric {omega}-2{theta} x-ray diffraction scans and reciprocal space maps reveal the presence of a strain gradient in these layers despite the apparently lattice-matched conditions. Transmission electron microscopy indicates that these cracks are the result of tensile stresses induced by crystallite coalescence and grain-boundary formation. This mechanism can be counteracted by augmenting the adatom mobility through increasing the growth temperature and the N flux. However, phase separation sets an upper limit on the growth temperature and a moderate increase to 350-400 deg. C is sufficient to obtain crack-free and homogeneous (Al,In)N layers. The results of our growth experiments lead to a phase diagram which shows the optimum growth window for (Al,In)N layers. By choosing the growth conditions within this window, we are able to obtain crack-free Al{sub 0.82}In{sub 0.18}N/GaN multilayers with abrupt interfaces.« less
  • Nonpolar (1120) Al{sub 0.2}Ga{sub 0.8}N/GaN multiple quantum wells (MQWs) have been grown by molecular beam epitaxy on (1120) Zn{sub 0.74}Mg{sub 0.26}O templates on r-plane sapphire substrates. The quantum wells exhibit well-resolved photoluminescence peaks in the ultra-violet region, and no sign of quantum confined Stark effect is observed in the complete multiple quantum well series. The results agree well with flat band quantum well calculations. Furthermore, we show that the MQW structures are strongly polarized along the [0001] direction. The origin of the polarization is discussed in terms of the strain anisotropy dependence of the exciton optical oscillator strengths.
  • The edge and threading dislocations of M-plane GaN epilayers grown on {gamma}-LiAlO{sub 2} have been studied by high-resolution transmission electron microscope. We found that edge dislocations were grown in [1100] direction while threading dislocations were generated along a{sub 1} or -a{sub 2} axes. We also observed a single stacking fault in the M-plane GaN epilayer.
  • The homoepitaxial growth of m-plane (1100) GaN was investigated by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions. The surface morphologies as a function of sample miscut were studied, providing evidence for a strong growth anisotropy that is a consequence of the anisotropy of Ga adatom diffusion barriers on the m-plane surface recently calculated ab initio[Lymperakis and Neugebauer, Phys. Rev. B 79, 241308(R) (2009)]. We found that substrate miscut toward [0001] implies a step flow toward <1126> while substrate miscut toward [0001] causes formation of atomic steps either perpendicular or parallel to the [0001] direction, under N-rich conditions at 730 degmore » C. We describe the growth conditions for achieving atomically flat m-plane GaN layers with parallel atomic steps.« less