Improvement in the crystallinity of ZnO thin films by introduction of a buffer layer

• Published in: Thin solid films 2002-05, Vol.411 (1), p.60-64
• Main Authors: Nakamura, Toshiyuki, Yamada, Yasusei, Kusumori, Takeshi, Minoura, Hideki, Muto, Hachizo
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallinity; Epitaxy; Exact sciences and technology; Laser deposition; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Pulsed laser deposition; Self-buffered ZnO film; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; ZnO thin film
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(02)00188-8

The influence of pre-deposition of homo-buffer layers on film quality is studied as functions of temperature and duration of pre-deposition, for zinc oxide (ZnO) crystalline films prepared by pulsed laser deposition on sapphire (0 0 0 1) substrates. This preparation technique is necessary to prepare high quality films suitable for the development of ZnO devices. Crystallinity and surface morphology were characterized by X-ray diffraction (XRD), reflection high energy electron diffraction and scanning electron microscopy. The line width of the rocking curve observed for ZnO (0 0 0 2) XRD of ZnO films decreases (to 0.09° from 0.2–0.3°) upon introduction of a buffer layer of ZnO itself at a low temperature approximately 500 °C, indicating the formation of high quality films. The surface morphology and flatness were also improved. The film prepared under optimal conditions shows a high optical transmittance of ∼90% with a steep falloff at 380 nm and a fairly small carrier concentration (1.8×10 17 cm −3). These results imply that the buffer layer relaxes the strain due to lattice mismatch between ZnO and sapphire (by 18%) and improves the film crystallinity.