Effect of Strain Gradation on Luminescence and Electronic Properties of Pulsed Laser Deposited Zinc Oxide Thin Films

• Published in: Journal of electroceramics Vol. 13; no. 1-3; pp. 345 - 352
• Main Authors: Rastogi, A C, Desu, S B, Bhattacharya, P, Katiyar, R S
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.07.2004
• Subjects: Annealing; Crystal defects; Film growth; Luminescence; Strain; Thin films; X-rays; Zinc oxide
• ISSN: 1385-3449; 1573-8663
• DOI: 10.1007/s10832-004-5124-9

Zinc oxide thin films on alpha-alumina substrates were prepared by the pulsed excimer laser ablation of a ZnO target at 1 mTorr pO2, and a substrate temperature of 750 C. Highly c-axis oriented films with optical transparency > 80% in the visible range were obtained. Strain distribution in the films was determined by line shape analysis of XRD data and by the broad luminescence features centred on the near band edge transition at 3.3 eV. Films were annealed at 800-900 C for 1 h in an oxygen atmosphere. Annealing at 850 C reduced the strain and the associated defects at the film/substrate interface. Full width at half maximum of X-ray rocking curves exhibited a reduction from 12.5 arc min to 9.0 arc min, confirming improved ZnO crystal quality. The omega-rocking curves exhibited two superimposed peaks, attributed to the interfacial layer and the bulk film. Graded strain in the film was attributed to the difference in orientation of the interfacial layer. The decrease in conductivity of the annealed films was attributed to oxygen vacancies as the primary defects. The formation of strain-free oriented optical quality films based on growth at low pO2 followed by annealing at high pO2 is proposed. 30 refs.