Atomic arrangement at the AlN/ZrB2 interface

Abstract

Low-dislocation-density GaN films (∼108 cm−2) have been grown on closely lattice-matched ZrB2 substrates by metalorganic vapor phase epitaxy using low-temperature AlN as a buffer layer. High-resolution electron microscopy images of the AlN/ZrB2 interface region reveal that the AlN buffer layer does not grow directly on the ZrB2 substrate. Instead, the existence of an unintentional intermediate cubic-phase layer (approximately 2 nm thick) has been observed. Misfit dislocations are evident at both interfaces of the intermediate layer. Our analysis indicates that the intermediate layer has a lattice constant a=4.6 Å, and that it is a ternary alloy of ZrxByNz, which should result from a transformation from the hexagonal phase of ZrB2 due to interdiffusion of nitrogen and boron at the elevated temperature required for growth of GaN. This intermediate cubic-phase layer of ZrxByNz appears to have been so far unavoidable in the growth of high-quality GaN epilayers on ZrB2 substrates by our technique.

Kinetic Role of Carbon in Solid-State Synthesis of Zirconium Diboride using Nanolaminates: Nanocalorimetry Experiments and First-Principles Calculations

“…Examples include its use as a substrate for group III nitride semiconductors in optoelectronic devices [1][2][3][4][5] , as support material for low-temperature fuel cells 6,7 , and as a hydrogen storage medium 8 . Difficulties associated with synthesis, however, have hindered broad adoption of the material -production of high-density ZrB 2 typically requires both extremely high temperature and pressure 9 because of its high melting point and stability.…”

Lattice‐matched interface between GaN and ZrB 2

“…The interfacial B-N bond formation changes the character of B-B bonds in the hexagonal B-plane from sp 2 to sp 3 , and consequently the interfacial B-plane reveals zigzag relaxation. This structural change may be relevant to the recent experimental observation that intermediate cubic-phase layers appear in AlN/ZrB2 interface [3].…”

“…For instance, there are always possibilities that nitrogens come into the ZrB 2 substrate during epitaxy. Therefore the B-N bond formation and change of the bond character will cause BN-like (or Zr x B y N z -like [3]) lattice-mismatched interfacial region. This may be a possible mechanism of the recent experimental observation that intermediate cubic-phase layers appear in AlN/ZrB 2 interface during MOVPE growth [3].…”

“…Therefore the B-N bond formation and change of the bond character will cause BN-like (or Zr x B y N z -like [3]) lattice-mismatched interfacial region. This may be a possible mechanism of the recent experimental observation that intermediate cubic-phase layers appear in AlN/ZrB 2 interface during MOVPE growth [3]. These results indicate that suppression of B-N bond formation is a key point for the effective use of ZrB 2 as a substrate for the epitaxial growth of GaN.…”

“…To improve the quality of GaN single crystals, many efforts are paid to devise growth techniques as well as to search more suitable, namely lattice-and thermal-expansion-coefficient-matched, substrates. Recently, Kinoshita et al [1] have reported that ZrB 2 is a promising substrate for epitaxial growth of GaN, because it has hexagonal (AlB 2 -type) structure, the lattice-mismatch is only 0.6%, and the thermal expansion coefficient is very close to that of GaN [1][2][3]. Furthermore, since ZrB 2 is a metallic compound with highelectrical and -thermal conductivity [1,2], the substrate may be used directly as a part of GaN-based devices.…”