The Effect of Hydrogen on the Molecular-Beam-Epitaxy Growth of GaN on Sapphire Under Ga-Rich Conditions

Buczkowski, S. L.; Yu, Zhonghai; Richards‐Babb, Michelle; Giles, N. C.; Romano, Lucia; Myers, T. H.

doi:10.1557/proc-449-197

Cited by 12 publications

(6 citation statements)

References 15 publications

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“…As has been previously observed [2][3][4], the RHEED image abruptly changes from spotty to streaky as flux conditions move from nitrogen-rich to gallium-rich. The surface morphology of films grown on GaN buffer layers and under various flux conditions is shown in Figure 1.…”

Section: Gan Buffer Layerssupporting

confidence: 70%

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

et al. 1998

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The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and "loop" defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS.

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Section: Gan Buffer Layerssupporting

confidence: 70%

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

et al. 1998

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“…6,11 Locally flat surfaces can be achieved on both polarities by MBE under slightly Ga-rich conditions, but special steps need to be taken to produce films that are free of inversion domains, and there are few reported procedures for doing so. 12,13 Lateral overgrowth of inversion domains is routine in MOVPE films, where the Ga-face matrix overgrows N-face columnar domains near the film-substrate interface, forming ''house-like'' structures that are observable by transmission electron microscopy ͑TEM͒. 14, 15 Here we report on the possibility of producing inversion-domainfree ͑homopolar͒ films by over growing the inversion domains under highly Ga-rich growth conditions.…”

Section: Introductionmentioning

confidence: 86%

“…13,16,17 Growth under conditions of a slight excess of Ga is known to lead to locally flat GaN surfaces and streaky RHEED patterns while growth under Ga-deficient conditions results in spotty, faceted RHEED images and rough surfaces. Stoichiometric growth conditions are taken to be where the growth mode abruptly transforms from two dimensional to three dimensional.…”

Section: A Growth Under Stoichiometric and Ga-rich Conditionsmentioning

confidence: 99%

Morphology, polarity, and lateral molecular beam epitaxy growth of GaN on sapphire

Piquette¹,

Bridger²,

Bandić³

et al. 1999

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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Gallium nitride was grown on sapphire ͑0001͒ substrates by radio frequency plasma assisted molecular beam epitaxy. The surface morphology was characterized during growth by reflection high energy electron diffraction, and ex situ by scanning electron microscopy ͑SEM͒, atomic force microscopy ͑AFM͒ and x-ray diffraction. It is found that surface morphological features are linked to domains of specific wurtzite crystal polarity, ͑0001͒Ga face or (0001 )N face, for Ga-rich growth. For growth on AlN buffer layers, we commonly observe films which consist of largely ͑0001͒Ga polarity material, as confirmed by selective etch tests, with a varying coverage of (0001 )N-face inversion domains threading along the growth direction. For growth near stoichiometric conditions, the growth rate of the N-face domains is slightly lower than that for the Ga-face matrix, which results in the formation of pits with inversion domains at their centers. For samples grown by first depositing GaN under N-rich conditions, followed by growth under Ga-rich conditions, a different morphology is obtained, exhibiting large hexagonal flat terraces observable by SEM and AFM. The apparent grain size of these films is increased substantially over films grown using a single step approach. The cross sectional SEM images of the two-step films show a network of voids and columns at the interface between the N-rich and the Ga-rich layers, above which micron-scale islands form and coalesce via lateral growth. Lateral growth may result in reduced defect density and improved crystal quality. The asymmetric x-ray peak (112 4) width is reduced to approximately 280 arcsec in the two-stage GaN films.

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“…Ammonia and carrier gasses are the source of hydrogen to the MOVPE process in a viscous flow pressure regime. Although the presence of hydrogen in the molecular flow pressure regime of MBE may have some influence on the surface morphology of undoped GaN layers, addition of hydrogen to the nitrogen plasma does not provide a similar effect in the magnesium doping MBE grown GaN [16,17]. A conversion in the PL spectrum to the characteristic blue has not been observed following post-growth annealing of MBE deposited magnesium doped material.…”

Section: Epitaxial Layer Surface Morphology and Magnesium Dopingmentioning

confidence: 96%

A Critical Comparison Between MOVPE and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device Applications

Johnson

Brown

et al. 1999

MRS Internet j. nitride semicond. res.

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A systematic study of the growth and doping of GaN, AlGaN, and InGaN by both molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) has been performed. Critical differences between the resulting epitaxy are observed in the p-type doping using magnesium as the acceptor species. MBE growth, using rf-plasma sources to generate the active nitrogen species for growth, has been used for III-Nitride compounds doped either n-type with silicon or p-type with magnesium. Blue and violet light emitting diode (LED) test structures were fabricated. These vertical devices required a relatively high forward current and exhibited high leakage currents. This behavior was attributed to parallel shorting mechanisms along the dislocations in MBE grown layers. For comparison, similar devices were fabricated using a single wafer vertical flow MOVPE reactor and ammonia as the active nitrogen species. MOVPE grown blue LEDs exhibited excellent forward device characteristics and a high reverse breakdown voltage. We feel that the excess hydrogen, which is present on the GaN surface due to the dissociation of ammonia in MOVPE, acts to passivate the dislocations and eliminate parallel shorting for vertical device structures. These findings support the widespread acceptance of MOVPE, rather than MBE, as the epitaxial growth technique of choice for III-V nitride materials used in vertical transport bipolar devices for optoelectronic applications.

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The Effect of Hydrogen on the Molecular-Beam-Epitaxy Growth of GaN on Sapphire Under Ga-Rich Conditions

Cited by 12 publications

References 15 publications

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

Morphology, polarity, and lateral molecular beam epitaxy growth of GaN on sapphire

A Critical Comparison Between MOVPE and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device Applications

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