Abstract
The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles ranging from 0° to 8° by using the atmospheric pressure meta–organic chemical vapor deposition (APMOCVD) technique. Morphology analysis revealed that the formation of the ZnO films on vicinal surfaces with small off-axis angles (1.4°–3.5°) follows the mixed growth mode: from one side, ZnO nucleation still occurs on wide (0001) terraces, but from another side, step-flow growth becomes more apparent with the off-cut angle increasing. We show for the first time that the off-cut angle of 8° provides conditions for step-flow growth of ZnO, resulting in highly improved growth morphology, respectively structural quality. Temperature-dependent photoluminescence (PL) measurements showed a strong dependence of the excitonic emission on the off-cut angle. The dependences of peak parameters for bound exciton and free exciton emissions on temperature were analyzed. The present results provide a correlation between the structural and optical properties of ZnO on vicinal surfaces and can be utilized for controllable ZnO heteroepitaxy on SiC toward device-quality ZnO epitaxial layers with potential applications in nano-optoelectronics.
Highlights
It is evident that the existing secondary nucleation makes the zinc oxide (ZnO) film surface quite rough
By changing the off-axis angle from 0◦ to 8◦, we showed a principal possibility to change the structural quality of ZnO layers: from a columnar structured film to a high-quality c-axis tilted ZnO layer without a grained structure
An off-axis angle of 8◦ was identified to promote the step-flow growth of ZnO layers with improved optical properties and no evidence of structural defects-involved electronic transitions
Summary
Received: 28 January 2021Accepted: 18 February 2021Published: 22 February 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/).There is a long-standing interest in implementing zinc oxide (ZnO) into realistic optoelectronic applications [1,2,3,4,5,6,7,8]. Numerous existing theoretical and experimental studies were mainly triggered by its unique optical properties, especially large exciton binding energy (60 meV) at room temperature (RT), which is even higher than that of GaN. This makes
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