Interaction Between Basal Stacking Faults and Prismatic Inversion Domain Boundaries in GaN
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Interaction Between Basal Stacking Faults and Prismatic Inversion Domain Boundaries in GaN
Philomela Komninou, Joseph Kioseoglou, Eirini Sarigiannidou, George P. Dimitrakopulos, Thomas Kehagias, Alexandros Georgakilas1, Gerard Nouet2, Pierre Ruterana2 and Theodoros Karakostas Physics Department, Aristotle University of Thessaloniki, Thessaloniki, GR-54006, Greece 1 IESL/FORTH and Physics Department, University of Crete, Heraklion-Crete, P.O.Box 1527, 71110, Greece 2 ESCTM-CRISMAT, UMR6508-CNRS, ISMRA Caen Cedex, 6 boul. du Marechal Juin, 14050, France ABSTRACT
The interaction of growth intrinsic stacking faults with inversion domain boundaries in GaN epitaxial layers is studied by high resolution electron microscopy. It is observed that stacking faults may mediate a structural transformation of inversion domain boundaries, from the low energy types, known as IDB* boundaries, to the high energy ones, known as Holt-type boundaries. Such interactions may be attributed to the different growth rates of adjacent domains of inverse polarity.
INTRODUCTION
GaN is a III-V semiconductor that has generated considerable interest for future applications in optoelectronic devices, due to its large direct band-gap [e.g. 1, 2, 3]. It is challenging that devices comprising this material function satisfactorily despite the large density of structural defects; for example, the density of threading dislocations in GaN thin films is approx. 1010 cm-2 [4]. Other common structural defects in GaN films are basal and prismatic stacking faults (SFs), nanopipes and prismatic inversion domain boundaries (IDBs) [e.g. 5, 6]. With respect to {1010} IDBs in particular, two principal types have been distinguished and observed [e.g. 7, 8]; the first, termed IDB*, is a low energy defect that does not introduce electronic states in the band gap. The second, termed Holt IDB, has considerably higher formation energy and should have an adverse effect on electronic properties due to the “wrong” bonds along the boundary [7]. The two IDB types are obtained from the Austerman-Gehman IDB [9] by applying a rigid-body translation to the abutting domains as described below. Epitaxial GaN usually crystallizes with the wurtzite structure that comprises two interpenetrating hcp substructures of distinct atomic species. These substructures are oriented in a parallel manner and are relatively displaced by 3/8[0001]. In the Austerman –Gehman IDB model, the substructure of one atomic species remains undisplaced across the boundary while the other species switches to inverse sites. In the Holt model, the atomic species are interchanged upon crossing the IDB; the corresponding rigid-body translation is 3/8[0001]. For the IDB* G3.44.1
model, a 1/2[0001] translation is added to the Holt model; thus, with respect to the Austerman – Gehman IDB, the rigid-body translation is –1/8[0001]. The present report aims to focus on the reasons for the introduction of Holt IDBs that are observed in GaN epilayers grown on sapphire by MBE [10]. In particular, we are concerned with in
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