Selective Area Growth of GaN Directly on (0001) Sapphire by the HVPE Technique
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Internet Journal Nitride Semiconductor Research
Selective Area Growth of GaN Directly on (0001) Sapphire by the HVPE Technique Raj Singh 1, Richard J. Barrett1, John J. Gomes1, Ferdynand P. Dabkowski 1 and T.D. Moustakas2 1Laser
Diode Manufacturing and Development, Polaroid Corporation,
2Department of Electrical and Computing Engineering and Center for Photonics Research, Boston University,
(Received Monday, June 22, 1998; accepted Monday, August 24, 1998)
In this paper, we report on the selective area growth (SAG) of GaN directly on patterned c-plane sapphire substrates by hydride vapor phase epitaxy (HVPE). A number of researchers have reported that the HVPE growth technique, unlike the MBE and MOCVD methods, is capable of producing device quality GaN films without the need for any low temperature nucleation/buffer layers. The density of edge dislocations in these HVPE films decreases dramatically as the film thickness is increased, and the dislocation density values for thick films (> 10µm) are comparable to those reported for the best GaN films grown by other methods on c-sapphire. These advantages of the HVPE growth technique makes it possible to achieve high quality selective area growth of GaN directly on c-sapphire substrates. C-plane sapphire substrates were coated with PECVD SiO2 and photolithographically patterned with different size and shape openings. Subsequently, these patterned substrates were introduced in a horizontal, hot-wall quartz reactor for the GaN growth. It was observed that single crystal GaN growth was preferentially initiated in the openings in the oxide layer. This selective area growth was followed by epitaxial lateral overgrowth (ELO), leading to the formation of hexagonal GaN prisms terminated in smooth, vertical (1100) facets. We have been successful in shearing these pyramid structures from the sapphire substrates as individual devices, which do not require any post-growth etching for feature definition. This procedure allows for the dramatic reduction of the process complexity and the duration and expense for GaN growth for device applications. Stimulated emission results on these self-formed optical cavities are also presented.
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Introduction
In recent years, there has been renewed interest in the Hydride Vapor Phase Epitaxy (HVPE) method for the growth of GaN layers. This technique is capable of producing device quality GaN films without the need for any low temperature nucleation/buffer layers. The density of edge dislocations in the HVPE grown GaN films decreases dramatically as the film thickness is increased (> 10µm), and the dislocation density values (~ 108 cm2) are comparable to those reported for the best GaN films grown by other methods [1]. A number of recent studies have indicated that the crystalline quality of heteroepitaxial GaN films can be further improved by epitaxial lateral overgrowth (ELO) on patterned GaN substrates [2-5]. This technique involves the heteroepitaxial growth of a GaN layer on sapphire or SiC substrate. This step is followed by the dep
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