Effect of Magnesium and Silicon on the lateral overgrowth of GaN patterned substrates by Metal Organic Vapor Phase Epita
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Internet Journal Nitride Semiconductor Research
Effect of Magnesium and Silicon on the lateral overgrowth of GaN patterned substrates by Metal Organic Vapor Phase Epitaxy S. Haffouz1, B. Beaumont1 and Pierre Gibart 1 1Centre
de Recherche sur l'Hétéroépitaxie et ses Applications, CRHEA-CNRS,
(Received Thursday, June 4, 1998; accepted Thursday, July 16, 1998)
Metalorganic vapor phase epitaxy was used to achieve selective regrowth of undoped, Mg- and Sidoped GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. Hexagonal openings in the mask defined into 10 µm diameter circles separated by 5µm were used as a pattern for the present study. Uniform undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R {1101} facets, were achieved with a good selectivity. Si-doped GaN hexagonal pyramids delimited by vertical {1100} facets and (0001) top facet were obtained for a high SiH4 flow rate in the vapor phase. We found that the GaN growth rates VR and VC, measured in the R 〈1101〉 and C 〈0001〉 directions respectively, were drastically affected by the Mg and Si incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/ VC ratio can be increased. Hence, the delimiting top C facet do not vanish as usually observed in undoped GaN selective regrowth but conversely expands. On the other hand, under proper growth conditions, 20µm-high Si-doped GaN columns were obtained.
1
Introduction
The successful development of short wavelength light emitting diodes and the more recent realization of nitride semiconductor lasers have stimulated great interest in the application of these materials for blue and ultraviolet optoelectronic devices [1]. Due to their large lattice mismatches with sapphire or 6H-SiC, nitrides epitaxial layers contain a large density of extended defects (109-1010 dislocations·cm-2) despite the use of a two-step growth method [2] [3] [4]. It has been demonstrated that a three dimensional (3D) growth mode leads to the reduction of the defects densities in the 108 cm-2 range [5] [6]. Recently, a significant reduction in the dislocation densities in GaN films was achieved via lateral mask overgrowth [7] [8]. Because of the growth rate anisotropies, the selective growth of GaN using hexagonal mask openings has led to the formation of GaN hexagonal pyramids delimited by six {1101} facets. Generally, the growth rate (VC) of the C (0001) facets is higher than that of the R {1101} facets. Therefore the coalescence of these hexagonal pyramids is very difficult. We have recently used two growth techniques, MOVPE and Halide Vapour Phase Epitaxy (HVPE),
respectively, in order to achieve selective growth of GaN and lateral overgrowth until coalescence of the islands [9]. Assessment by X-ray diffraction has showna FWHM in ω scan of 50 arsec on the flat part of an HVPE overlayer . Recently, Kapolnek et al. [10] reported that a maximum epitaxial lateral mask overgrowth can be obtained at high temperature and ammonia flow. Magnesium was
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