Low-energy electron microscopy observations of GaN homoepitaxy using a supersonic jet source

Pavlovska, A.; Torres, Víctor; Bauer, E.; Doak, R. Bruce; Tsong, I. S. T.; Thomson, D. B.; Davis, R. F.

doi:10.1063/1.124575

Cited by 16 publications

(7 citation statements)

References 13 publications

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“…We believe that the absence of As and other impurities in the present Auger measurements is more evidence of the Ga-adatom model we have proposed. The 2 3 2 observed by us as well as by others [8] …”

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confidence: 58%

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Xueet al.Reply:

et al. 2000

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Xue et al. Reply: In their Comment [1] on our recent Letter [2], Ramachandran et al. argue that As is present in our molecular beam epitaxy (MBE) system since it was previously used for the As-based material growth and that the As indeed stabilized the reconstructions of the Ga-polar GaN(0001) surface we reported. Their claim is based on the facts that they did not observe the 2 3 2 and other structures in their As-free MBE system [3] and that the 2 3 2 was observed by their reflection high energy electron diffraction (RHEED) measurements, not by scanning tunneling microscopy (STM), when they intentionally introduced As during the growth of GaN [1].We have to respectfully disagree with their argument, based on our in situ Auger electron spectroscopy (AES) measurements (Fig. 1). We conclude that the 2 3 2, 4 3 4, 5 3 5, and other reconstructions we reported in the Letter are free of As (within our AES sensitivity), and that the As adatom model proposed by them [1] cannot explain our results.We performed the AES study for the 2 3 2, 4 3 4, and 5 3 5 reconstructions of the GaN(0001) formed on the Siterminated 6H-SiC and sapphire substrates using a LEED/ AES setup (ULVAC-PHI) incorporated to the STM chamber. Figure 1(a) is the result for the GaN͑0001͒-5 3 5 reconstruction. Qualitatively the identical results are obtained for the other surfaces. The spectrum is dominated with the Ga LMN peak at about 1071 eV, and the Asrelated feature is absent, whose most intense Auger emission should appear at about 1230 eV. We repeated the Auger scans from 1100 eV in order to avoid the adverse effect from possible electron-induced desorption, and the results were the same. In order to test the sensitivity and

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confidence: 58%

“…In the case of the N-polar ͑0 0 0 1͒ surface, we observed the 6 3 6 by RHEED and STM, and the obtained donut-shaped STM image is exactly the same as that reported by Smith et al [7] using the As-free system. As for the 2 3 2, other groups reported it even under the As-free system [8].…”

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confidence: 89%

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“…A similar morphology for a 4-nm-thick GaN layer grown on SiC at 650 • C under Ga-rich growth conditions has also been reported recently by Ramachandran et al 16 The requirement of Ga-rich growth condition for producing smooth basal-planeoriented GaN layers has been previously noted. 9,17,18 However, the growth temperatures were higher in those studies, in the range of 650-800 • C. We conclude that the Ga/NH 3 flux ratios employed to achieve growth of nonfaceted GaN buffer layers by MBE are strongly dependent on the growth temperature. At lower growth temperatures, i.e.…”

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confidence: 78%

“…The experimental configuration for conducting MBE growth of GaN inside the LEEM has been described previously 3,9,10 and is shown in Fig. 1.…”

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confidence: 99%

MORPHOLOGICAL CONTROL OF GaN BUFFER LAYERS GROWN BY MOLECULAR BEAM EPITAXY ON 6H–SiC(0001)

Smith

Doak

et al. 2000

Surf. Rev. Lett.

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The growth of GaN buffer layers of thickness 10-25 nm directly on 6H-SiC(0001) substrates was studied using low energy electron microscopy, atomic force microscopy and cross-sectional transmission electron microscopy. The Ga flux was supplied by an evaporative source, while the NH3 flux came from a seeded beam supersonic jet source. By monitoring the growth in situ and by suitably adjusting the Ga/NH3 flux ratio, smooth basal-plane-oriented GaN layers were grown on hydrogen-etched SiC substrates at temperatures in the range of 600-700 • C. The growth proceeds via nucleation of small flat islands at the step edges of the 6H-SiC(0001) substrate surface. The islands increase in size with a lateral-to-vertical growth ratio of ∼ 10 and eventually coalesce into a quasicontinuous layer. A highly defective substrate surface was found to be detrimental to the growth of flat buffer layers.

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“…Tarsa et al, 5 who grew homoepitaxial GaN͑0001͒ films by plasma-assisted MBE at 750°C and Pavloska et al, 6 who grew homoepitaxial GaN͑0001͒ films by supersonic jet epitaxy (SJE) using NH 3 -seeded beams at substrate temperatures of 655-710°C, reported similar 3D-2D transitions. Tarsa et al, 5 who grew homoepitaxial GaN͑0001͒ films by plasma-assisted MBE at 750°C and Pavloska et al, 6 who grew homoepitaxial GaN͑0001͒ films by supersonic jet epitaxy (SJE) using NH 3 -seeded beams at substrate temperatures of 655-710°C, reported similar 3D-2D transitions.…”

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confidence: 92%

Surface-roughness correlations in homoepitaxial growth of GaN(0001) films by NH3 supersonic jet epitaxy

Smith

Lamb

McGinnis

et al. 2004

Journal of Applied Physics

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Homoepitaxial GaN films were grown on GaN(0001)∕6H-SiC substrates by NH3 supersonic jet epitaxy at 750°C using a constant Ga flux of 2.9×1014cm−2s−1 and varying the NH3 flux and average kinetic energy. Atomic force microscopy (AFM), scanning electron microscopy, and in situ reflection high-energy electron diffraction evidence an abrupt transition from quasi-two-dimensional basal-plane growth to three-dimensional faceted growth at approximately 1∕2 of the maximum Ga-limited growth rate, irrespective of NH3 kinetic energy. Topographical scaling analysis of the AFM images reveals that the smooth and rough GaN(0001) films have static scaling exponents (α) of 0.88±0.05 and 1.10±0.06, respectively. The dynamic scaling exponent (β) for rough films is approximately 0.25. A comparison of these scaling exponents with predictions based on continuum growth models indicates that competition between surface diffusion and stochastic roughening governs the evolution of surface morphology during GaN growth.

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Low-energy electron microscopy observations of GaN homoepitaxy using a supersonic jet source

Cited by 16 publications

References 13 publications

Xueet al.Reply:

Xueet al.Reply:

MORPHOLOGICAL CONTROL OF GaN BUFFER LAYERS GROWN BY MOLECULAR BEAM EPITAXY ON 6H–SiC(0001)

Surface-roughness correlations in homoepitaxial growth of GaN(0001) films by NH3 supersonic jet epitaxy

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