Growth and stability of rocksalt Zn1-xMgxO epilayers and ZnO/MgO superlattice on MgO (100) substrate by molecular beam epitaxy

摘要

Zn1-xMgxO films with x = 0.04-0.50 grown on MgO (100) substrates by molecular beam epitaxy retain the rocksalt (rs) crystal structure and grow epitaxially for x >= 0.17. In addition, the rs-ZnO epilayer is observed to be stable up to a thickness of 5 nm and also in a ZnO/MgO superlattice sample. However, a portion of the superlattice has transformed to wurtzite (wz)-structure islands in a self-accommodated manner during growth. The transformation is a combination of a Bain distortion, an in-plane rotation of 14.5 degrees, and a Peierls distortion, resulting in an orientation relationship of (100) rs//(10 (1) over bar0)(wz) and < 011 >(rs) similar to//<(1) over bar2 (1) over bar3 >(wz). In such a manner, the volume expansion is only necessary along the growth direction and the in-plane strains can be minimized. A negative pressure generated during the transformation of ZnO stabilizes the MgO into a wurtzite structure. Published by AIP Publishing.