Surface Morphology and Composition Characterization at the Initial Stages of AlN Crystal Growth

Liu, B.; Shi, Ying; Liu, L.; Edgar, James H.; Braski, D.N.

doi:10.1557/proc-639-g3.13

Cited by 6 publications

(6 citation statements)

References 9 publications

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“…Seeded growth of AlN on SiC substrates looks very promising since high quality up to 4 inch SiC substrates are available. It was reported recently by a few groups [4][5][6][7] that heteroepitaxial seeding of AlN on SiC is easier to achieve than homoepitaxial seeding, but the reasons are still under discussion. In this paper we investigate the initial stages of seeded PVT growth of AlN on SiC.…”

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confidence: 99%

Initial growth stage in PVT growth of AlN on SiC substrates: Influence of Al₂O₃

Heimann¹,

Pfeiffer²,

Bickermann³

et al. 2007

Phys. Status Solidi (c)

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After the first 2 minutes of growth, the substrate surface demonstrates two areas with very different morphologies: (I) regular arrays of hexagonal hillocks with 3D crystallites of AlN growing well oriented on hillock tops and (II) flat areas with very smooth surface where AlN grows in 2D layered mode. The addition of Al 2 O 3 enhances the second growth mode (II), presumably because of surface melting in a very initial stage of growth. Surface morphologies in these single crystalline layers were studied using scanning electron microscopy (SEM). Chemical composition of selected areas was identified by Auger electron spectroscopy (AES). A chemical model is proposed to explain the obtained layer morphology.1 Motivation The development of (opto-) electronic devices based upon wide band gap group-III nitrides has received much attention due to their potential in short wavelength emission and detection as well as in high power high frequency microwave devices [1]. As a consequence of its close physical, chemical and structural nature to aluminum gallium nitride (AlGaN) from which epilayers are employed in this field, aluminum nitride (AlN) is an excellent candidate as a III-nitride substrate material [2]. Recently, we reported on freestanding AlN crystals, large enough for wafering, grown by PVT technique [3]. Still there are some major problems that need to be solved such as stability of crucible materials at high growth temperatures, anisotropic growth rates varying at different temperatures, and difficulties of seeding due to oxygen contamination of source material. Seeded growth of AlN on SiC substrates looks very promising since high quality up to 4 inch SiC substrates are available. It was reported recently by a few groups [4][5][6][7] that heteroepitaxial seeding of AlN on SiC is easier to achieve than homoepitaxial seeding, but the reasons are still under discussion. In this paper we investigate the initial stages of seeded PVT growth of AlN on SiC. Furthermore we propose a detailed model of the seeding process where oxygen plays a vital role.2 Experimental Crystal growth experiments have been performed by a sandwich sublimation PVT growth method inspired by a design by Vodakov et al. for PVT growth of SiC [8]. By using this technique Vodakov et al. were able to improve layer homogeneity and decrease growth temperatures as well as incorporation of impurities. In our arrangement dense ceramic items were machined from a bulk obtained by sintering commercially available AlN powder at temperatures between 2250-2300 °C in high-

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confidence: 99%

Initial growth stage in PVT growth of AlN on SiC substrates: Influence of Al₂O₃

Heimann¹,

Pfeiffer²,

Bickermann³

et al. 2007

Phys. Status Solidi (c)

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“…The seeds were coated with a 300 nm AlN epilayer deposited by MOCVD, which was intended to protect them from early decomposition and to promote two-dimensional nucleation of AlN [6]. AlN layers of varying thickness, grown at different temperatures and for different times, were deposited on these seeds.…”

Section: Resultsmentioning

confidence: 99%

“…Bulk AlN crystals grown by the sublimation-recondensation technique have been reported [3,4], but presently, large AlN single crystals are still not available in large quantities. Seeded growth of AlN on SiC has been studied by a number of groups [2,[5][6][7] as a way to exploit the availability of large, high-quality SiC substrates and to control the polarity and orientation of AlN crystals. These studies identified a number of issues associated with this technique, including the stability of the SiC seeds, the growth mode of AlN, the presence of defects in the grown layers, and postgrowth cracking of the AlN layers due to the thermal expansion coefficient mismatch.…”

Section: Introductionmentioning

confidence: 99%

Polarity and morphology in seeded growth of bulk AlN on SiC

Dalmau

Schlesser

Sitar

2005

phys. stat. sol. (c)

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Growth of AlN bulk crystals on on-axis and off-axis (0001), Si-face SiC seeds was performed by physical vapor transport (PVT) using an AlN powder source. AlN layers between 0.1-3 mm thickness were grown on inch-sized seeds. Cracks formed in the AlN layers due to the thermal expansion mismatch between AlN and SiC were observed to decrease with increasing AlN thickness. AlN grown on on-axis SiC was primarily Al-polar, but contained N-polar inversion domains (IDs) revealed buy wet etching in hot, aqueous phosphoric acid or potassium hydroxide solutions. IDs were not observed in crystals grown on offaxis seeds. Using X-ray diffraction and scanning electron microscopy results, the influence of SiC seed orientation on the polarity and morphology of the AlN layers is discussed.

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“…The decomposition of 6H-SiC was discussed in detail in Ref. [8]. Such problems are avoided by first depositing an AlN layer by MOCVD.…”

Section: Resultsmentioning

confidence: 99%