Mg-enhanced lateral overgrowth of GaN on patterned GaN/sapphire substrate by selective Metal Organic Vapor Phase Epitaxy
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Internet Journal Nitride Semiconductor Research
Mg-enhanced lateral overgrowth of GaN on patterned GaN/sapphire substrate by selective Metal Organic Vapor Phase Epitaxy B. Beaumont1, M. Vaille1, G. Nataf1, A. Bouillé1, J.-C. Guillaume1, P. Vénnègues1, S. Haffouz1 and Pierre Gibart 1 1Centre
de Recherche sur l'Hétéroépitaxie et ses Applications, CRHEA-CNRS,
(Received Wednesday, July 22, 1998; accepted Thursday, September 10, 1998)
Selective and lateral overgrowth by Metal Organics Vapour Phase Epitaxy (MOVPE) was carried out until coalescence to produce smooth and optically flat thick GaN layers. A GaN epitaxial layer is first grown using atmospheric pressure Metalorganic Vapour Phase Epitaxy on a {0001} Al2O3. substrate. Then a 30Å silicon nitride dielectric film is deposited in-situ by reaction of silane and ammonia to form a selective mask. Afterwards, the openings and the figures in the dielectric films are achieved using standard photolithographic technology. Stripes openings in the mask, revealing free GaN surface, are aligned in the 〈1010〉 direction. Typical stripes spacing and width are 10 µm and 5 µm respectively. These patterned layers are further on used for epitaxial regrowth of GaN by MOVPE. The growth anisotropy and therefore the coalescence process is achieved by introducing (MeCp)2Mg in the vapour phase. A two-step process is reported which allows a dramatic reduction of threading dislocations density not only above the masked areas but also above the windows opened in the mask. With this process, very sharp bound exciton luminescence peaks are measured at low temperature in the overgrown GaN.
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Introduction
Selective epitaxy has been widely developed for III-V semiconductors like GaAs, InP or Si [1]. More precisely, selective epitaxy allows an accurate control of the size and the shape of the overgrowth and therefore leads to the fabrication of quantum structures (quantum wire and quantum dots). Selective epitaxy in heteroepitaxial systems like GaAs/Si [2] or InP/Si [3] has also been widely used to overcome the deleterious effect of the large lattice mismatch. Selective epitaxy of GaN by both MOVPE and HVPE on patterned GaN on sapphire has been previously reported [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]. Selective epitaxy corresponds to spatially controlled growth of an epitaxial layer through openings in a masking material, which is typically a dielectric such as silicon oxide or nitride. Growth anisotropy corresponds to the occurrence of different growth velocities on different crystallographic planes. This has been observed in HVPE since at least two decades ago. For instance in GaAs there are two orders of magnitude difference between the growth rates of {111}Ga and
{111}As. These features are understood by analyzing the orientation dependence of the growth rate associated with surface kinetics. Growth anisotropy in MOVPE occurs only when diffusing molecules encounter different surface orientation within their mean free path λs. A major problem in selective epitaxy is the a
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