Interfacial structure of semipolar AlN grown on m -plane sapphire by MBE

Abstract

The interfacial properties of ð1122Þ AlN epilayers grown on m-plane sapphire by plasma-assisted molecular-beam epitaxy (PAMBE) were investigated in the context of achieving highquality semipolar GaN/AlN heterostructures with reduced internal polarization. Epilayers grown under metal-rich conditions with and without nitridation pre-treatment of the sapphire surface were compared using transmission electron microscopy (TEM). In addition to the dominant semipolar orientation, the films exhibited an interfacial zone comprising AlN nanocrystals with the m-plane orientation. The size of the nonpolar nanocrystals increased significantly with sapphire nitridation. A good epitaxial relationship with the substrate was attained by both the semipolar as well as the nonpolar AlN. However, the interfacial structure was perturbed by interfacial roughness and pit formation. The surface nanofacets were correlated to the increased introduction of nanocrystals with m-plane orientation.

High temperature chemical vapor deposition of aluminum nitride, growth and evaluation

“…4b), the (0001) texture is predominant. The angle between (0001) and (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) planes is 78.44°. It means that a cross-section of a (21-31) plane must show more (0001) planes than non-polar planes which is in agreement with our observations.…”

“…2). Above 1300°C, preferred orientations are obtained and change from the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) to the (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) and finally the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) plane normal to the substrate surface with increasing deposition temperature. Both the evolution of grain size and texture of such AlN layers can be explained by the Van der Drift's evolutionary selection growth mechanism [40].…”

“…3a. The (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) semi-polar planes are represented in Fig. 3b.…”

“…The use of thick coatings of high-Z materials like tungsten (W) or tungsten alloys (W 1 − x Re x ) is a promising solution to overcome (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and (10-10) non-polar planes and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31) semi-polar planes are represented. In this study, preferred orientations obtained for thick polycrystalline AlN layers are (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), (21)(22)(23)(24)…”

“…It was successfully developed by Slack and McNelly [13,14] in the mid-1970s. Several methods such as pulsed laser deposition (PLD) [15], chemical vapor deposition (CVD and MOCVD) [16] or hydride vapor phase epitaxy (HVPE) [17][18][19][20], molecular beam epitaxy (MBE) [21] and magnetron sputtering [22] have been employed for deposition of AlN thin or thick films for different applications. Important issues for deposition techniques [23][24][25][26] of the functional layers are: (1) large area deposition; (2) crystallinity of the grown layers; (3) residual stress and strain; (4) strain gradients in the multilayer architecture and (5) surface and interface morphology.…”