Structural Stabilization and Piezoelectric Enhancement in Epitaxial (Ti1−xMgx)0.25Al0.75N(0001) Layers
Abstract
Epitaxial (Ti1−xMgx)0.25Al0.75N(0001)/Al2O3(0001) layers are used as a model system to explore how Fermi‐level engineering facilitates structural stabilization of a host matrix despite the intentional introduction of local bonding instabilities that enhance the piezoelectric response. The destabilizing octahedral bonding preference of Ti dopants and the preferred 0.67 nitrogen‐to‐Mg ratio for Mg dopants deteriorate the wurtzite AlN matrix for both Ti‐rich (x x ≥ 0.9) alloys. Conversely, x = 0.5 leads to a stability peak with a minimum in the lattice constant ratio c/a, which is caused by a Fermi‐level shift into the bandgap and a trend toward nondirectional ionic bonding, leading to a maximum in the expected piezoelectric stress constant e33. The refractive index and the subgap absorption decrease with x, the optical bandgap increases, and the elastic constant along the hexagonal axis C33 = 270 ± 14 GPa remains composition independent, leading to an expected piezoelectric constant d33 = 6.4 pC N−1 at x = 0.5, which is 50% larger than for the pure AlN matrix. Thus, contrary to the typical anticorrelation between stability and electromechanical coupling, the (Ti1−xMgx)0.25Al0.75N system exhibits simultaneous maxima in the structural stability and the piezoelectric response at x = 0.5.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 04, 2020
- Source ID
- 10.1002/adfm.202001915
Entities
People
- Baiwei Wang
- Daniel Gall
- John T. Gaskins
- Kiumars Aryana
- Patrick E Hopkins
- S. V. Khare
Organizations
- National Science Foundation
- Office of Naval Research
- Rensselaer Polytechnic Institute
- University of Toledo
- University of Virginia