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

Abstract

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-

Liquid phase epitaxy (LPE) of GaN on c- and r-faces of AlN substrates

“…The nucleation takes place on top of these pyramids. A similar behaviour was observed during AlN epitaxy on SiC substrates [8]. After surface preparation 90% face coverage could be observed on single crystalline r-plane wafers.…”

Erlangen—An Important Center of Crystal Growth and Epitaxy: Major Scientific Results and Technological Solutions of the Last Four Decades

“…Their scientific results were published in a series of articles (see, e.g., refs. []). In 2010 the company CrystAl‐N was founded out of their research activities.…”

SiC seed polarity-dependent bulk AlN growth under the influence of residual oxygen

“…With a few exceptions [21,22] all published growth experiments have been carried out only on Si polar SiC.…”