Structures and Polarity of III‐Nitrides: Phase Diagram Calculations Using Absolute Surface and Interface Energies

Abstract

The structures and polarity of group‐III nitride semiconductors are theoretically investigated by calculating individual energy of polar surfaces and interfaces using density functional calculations. Using the surface and interface energies, we demonstrate phase diagrams as functions of temperature and pressure for polar AlN on 6H‐SiC(0001) substrate as well as polarity inversion of GaN on N‐polar AlN(0001¯) substrate. The calculated phase diagram for AlN on Si‐face SiC under H‐rich conditions reveals that the H‐terminated Al‐polar surfaces with substitutional Al atoms at AlN/SiC interface are stabilized over the wide range of Al pressure below 1320 K while that with N adatom are favorable for temperature beyond 1320 K. In contrast, the calculated phase diagram for GaN on N‐polar AlN(0001¯) substrate clarifies that the H‐terminated Ga‐polar surface with on N‐polar substrate with two monolayers of Al olverlayers is favorable over entire growth conditions. These results suggest that the stability of interface between III‐nitride and substrate rather than surface stability is crucial for the polarity of III‐nitrides.

Effect of Step Edges on Adsorption Behavior for GaN(0001) Surfaces during Metalorganic Vapor Phase Epitaxy: An Ab Initio Study

“…We consider various atomic configurations, as schematically shown in Figure . The models, barring the ideal vicinal GaN(0001) surface shown in Figure (a), are constructed on the basis of the electron counting (EC) rule and previously reported reconstructions on GaN(0001) surfaces under the MOVPE growth condition. ,,− In these models, terrace regions are constructed by multiplying the (2 × 2) periodicity satisfying the EC rule . The surfaces of periodic (2 × 9) vicinal slab models comprise two (2 × 4) terrace regions and two single layer steps.…”

Equilibrium Morphologies of Faceted GaN under the Metalorganic Vapor‐Phase Epitaxy Condition: Wulff Construction Using Absolute Surface Energies

“…To calculate absolute surface energies among various orientations on the basis of ab initio calculations, we use the wedge‐shape geometry method . Details of the calculation procedure are described elsewhere . H is determined by crossing point P and the angle θ , which is given by the surface orientation and tilted by nonpolar plane.…”

Epitaxial Junction of Inversion Symmetry Breaking AlN and Centrosymmetric NbN: A Polarity Control of Wide-Bandgap AlN

“…Both Al- and N-polar AlN with various atomic configurations on a γ-Nb 4 N 3 (112) surface (Figure a) were considered as possible interface structures. Figure b shows the calculated interface energies , between γ-Nb 4 N 3 and AlN as a function of Al chemical potential, μ Al . Herein, μ Al can vary in the thermodynamically allowed range described as μ Al bulk +Δ H ≤ μ Al ≤ μ Al bulk , where μ Al bulk is the chemical potential of bulk Al and Δ H (−2.91 eV) is the heat of formation for AlN.…”

“…Both Al-and N-polar AlN with various atomic configurations on a γ-Nb 4 N 3 (112) surface (Figure 5a) were considered as possible interface structures. Figure 5b shows the calculated interface energies 37,38 AlN with four N−Al bonds in the unit cell was stabilized over a wide range of growth conditions. The stabilization of the interface by N−Al bond formation is common for the interface between NbN x and AlN.…”