Optical Properties and Interband Transitions of ZnO and Cu-Doped ZnO Films Revealed by Spectroscopic Ellipsometry Measurement

Abstract:

Optical properties analysis of ZnO and Cu-doped ZnO films on Pt substrate have been probed by using Spectroscopic Ellipsometry (SE) at room temperature. Here, we study the optical transitions and the evolution of excitonic states by means of the critical points (CP) analysis. The second derivative spectra of dielectric function (CP analysis) show the transition of excitonic peak at the fundamental absorption edge (E₀). Corresponds to e₁ spectra, the peak of refractive index (n) at around 3.3 eV is broaden by introducing Cu dopant. This peak is assigned as excitonic states and the peak broadening is mainly due to the screening of excitons. This excitonic screening is more pronounced in the second derivative spectra of dielectric function where the peaks intensity is decreased upon Cu dopant. In additions, effective number of carrier concentrations of ZnO film shows a high number as high as ~10²² cm^-3. Furthermore, the addition of Cu doping -in this case 8 in at.%- does not significantly affect the effective number of ZnO film carrier concentration. This result confirms the strong interaction between ZnO film and Pt substrate and negligible contribution of Cu dopant for carrier concentration.

• Periodical: Advanced Materials Research (Volume 1112)
• Pages: 124-127
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.1112.124
• Online since: July 2015
• Authors: Resti Marlina, Andrivo Rusydi, Yudi Darma*
• Keywords: Critical Points, Dielectric Function, Optical Transitions, Spectroscopic Ellipsometry, ZNO

References

[1] A. Schleife, C. Rӧdl, F. Fuchs, J. Furthmuller, and F. Bechstedt, Optical and energy-loss spectra of MgO, ZnO, and CdO from ab initio any-body calculations, Phys. Rev. B, 80 (2009) 035112.

DOI: 10.1103/physrevb.80.035112

[2] S. W. Kim, Sz. Fujita and Sg. Fujita, Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition, Appl. Phys. Lett. 81 (2002) 5036.

DOI: 10.1063/1.1527690

[3] X. W. Sun and H. S. Kwok, Optical properties of epitaxially grown zinc oxide films on sapphire by pulsed laser deposition, J. Appl. Phys. 86 (1999) 408.

DOI: 10.1063/1.370744

[4] T.S. Herng, M.F. Wong, D. Qi , J. Yi , A. Kumar , A. Huang, F.C. Kartawidjaja, S. Smadici, P. Abbamonte, C. Sánchez-Hanke, S. Shannigrahi, J.M. Xue, J. Wang, Y.P. Feng, A. Rusydi, K. Zeng, J. Ding, Mutual Ferromagnetic–Ferroelectric Coupling in Multiferroic Copper‐Doped ZnO, Adv Mater. XX (2011).

DOI: 10.1002/adma.201004519

[5] L. Schmidt-Mende and J.L. MacManus-Driscoll, ZnO–nanostructures, defects, and devices, Mater. Today 10, 40 (2007).

DOI: 10.1016/s1369-7021(07)70078-0

[6] Y. Darma, T. S. Herng, R. Marlina, R. Fauziah, J. Ding and A. Rusydi, Interplay of Cu and oxygen vacancy in optical transitions and screening of excitons in ZnO: Cu films, Appl. Phys. Lett. 104 (2014) 08192.

DOI: 10.1063/1.4866029

[7] T. S. Herng , D. C. Qi , T. Berlijn , J. B. Yi , K. S. Yang , Y. Dai, Y. P. Feng , I. Santoso , C. Sánchez-Hanke , X. Y. Gao , A. T. S. Wee ,W. Ku , J. Ding , A. Rusydi , Room-Temperature Ferromagnetism of Cu-Doped ZnO Films Probed by Soft X-Ray Magnetic Circular Dichroism, Phys. Rev. Lett. 105 (2010).

DOI: 10.1103/physrevlett.105.207201

[8] H. Yoshikawa and A. Adachi, Optical Properties of ZnO, Jpn J Appl Phys. 36 (1997) 6237-6243.

[9] P.Y. Yu and M. Cardona, Optical Propertes I : Fundamental of Semiconductors 4th edition, Springer, New York, 2010, p.282.

[10] G.E. Jellison, Jr and L. A. Balner. Optical functions of uniaxial ZnO determined by generalized ellipsometry. Phys. Rev. B 58 (1998) 3586-5589; Erratum 65 (2001) 049902.

DOI: 10.1103/physrevb.65.049902