Thermodynamics of inversion-domain boundaries in aluminum nitride: Interplay between interface energy and electric dipole potential energy

Abstract

Aluminum nitride (AlN) has a polar crystal structure that is susceptible to electric dipolar interactions. The inversion domains in AlN, similar to those in GaN and other wurtzite-structure materials, decrease the energy associated with the electric dipolar interactions at the expense of inversion-domain boundaries, whose interface energy has not been quantified. We study the atomic structures of six different inversion-domain boundaries in AlN, and compare their interface energies from density functional theory calculations. The low-energy interfaces have atomic structures with similar bonding geometry as those in the bulk phase, while the high-energy interfaces contain N-N wrong bonds. We calculate the formation energy of an inversion domain using the interface energy and dipoles' electric-field energy, and find that the distribution of the inversion domains is an important parameter for the microstructures of AlN films. Using this thermodynamic model, it is possible to control the polarity and microstructure of AlN films by tuning the distribution of an inversion-domain nucleus and by selecting the low-energy synthesis methods.

Inversion Domain Boundaries in Wurzite GaN

“…2, there are sparse {1010} planes, conventionally called type 1, and dense {1010} planes, called type 2. Our calculations and previous works [29,30] indicate that for all studied cases of {1010} planar defects the type 1 defects are energetically favorable compared to the type 2 defects. Thus, in the rest of this document, unless explicitly stated otherwise any {1010} planar defect we discuss or illustrate will be of type 1.…”

First-Principles Understanding on the Formation of Inversion Domain Boundaries of Wurtzite AlN, AlScN, and GaN

“…The IDB model is constructed from the two grains with different polarized directions and has irregular distorted bonding structures unlike bulk wurtzite phase (Figure S1). 27,28 To confirm the reliability of the designed IDB models, the thermodynamic stability of IDB structures was examined by AIMD at 300 and 600 K. Figure S2 represents stabilized atomic structures of AlN, AScN, and GaN models at 300 and 600 K. The IDB models of all materials maintain the atomic arrangements of the IDBs at the grain boundary comparable to IDB models stabilized by DFT for both temperatures. Consequently, the IDB models are considered thermodynamically stable and structurally reliable.…”

“…24−26 The polycrystal-line wurtzite nitride growth results in the formation of both metal (e.g., Al, Ga, and Sc) polar and N polar grains that generate inversion domain boundaries (IDBs) between the grains of different polarities. 27 The IDBs were examined structurally to find reliable atomic arrangements. 28 However, the comprehensive characteristics of IDBs of these wurtzite nitrides have not been modeled even though the polycrystalline phase with IBDs is known to deteriorate the material properties (e.g., thermal, optical, and piezoelectric properties).…”

Review—Status and Challenges in Hetero-epitaxial Growth Approach for Large Diameter AlN Single Crystalline Substrates

“…Recently reported thermodynamics based first principle calculation of IDs showed that their interface energies are highly correlated with the structural distortions of bond lengths and bond angles. 108 Surface preparation and etching.-The preparation of nearlyatomically flat surface and the determination of the etching properties of AlN substrates as well is of great importance for their further usage in epitaxial growth and device preparation. Different polishing procedures were developed by various research groups based on mechanical and chemical-mechanical (CMP) processes.…”