Experimental verification of optical modulation with external stress has not been easily available in flexible systems. Here, we intentionally induced extra stress in wide band gap ZnO thin films by a unique prestress-driven deposition processing that utilizes a stretching mode. The stretching mode provides homogeneous but biaxial stresses in the hexagonal wurtzite structure, leading to the extension of the c-axis and the contraction of the a-axis. As a result, the reduction of the optical band gap by ∼150 meV was observed for the strain of ∼4.87%. The band gap narrowing was found to occur from the respective downward and upward shifts of the conduction band minimum and valence band maximum under the applied stress. The experimental evidence of optical modulations was supported by the theoretical calculations using density functional theory. The reduced strong interactions between Zn d and O p orbitals were assumed to be responsible for the band gap narrowing.
Bibliographical noteFunding Information:
This work was financially supported by the Samsung Research Funding Center of Samsung Electronics (SRFC-MA1502-12) and the Creative Materials Discovery Program by Ministry of Science and ICT (2018M3D1A1058536). Computational resources have been provided by the KISTI supercomputing center (KSC-2018-C3-0006) and the Australian National Computational Infrastructure (NCI).
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry