Sains Malaysiana 42(9)(2013): 1327–1332

Effects of the Nitric Acid Concentrations on the Etching Process, Structural

and Optical Properties of Porous Zinc Oxide Thin Films

(Kesan Kepekatan Asid Nitrik Terhadap Proses Pemunaran, Ciri-ciri Struktur

dan Optik Filem Nipis Zink Oksida Berliang)

C.G. Ching*, Leonard Lu, C.I. Ang, P.K. Ooi, S.S. Ng, Z. Hassan & H. Abu Hassan

Nano-Optoelectronic Research and Technology Laboratory, School of Physics,

Universiti Sains Malaysia, 11800, Penang, Malaysia

Received: 1 August 2012/Accepted: 16 December 2012

ABSTRACT

The present study reports on the fabrication of porous zinc oxide by wet chemical etching. ZnO thin films were deposited via radio-frequency magnetron sputtering on p-type silicon with (111) preferred orientation. The etchants used in the present work were 0.1% and 1.0% nitric acid (HNO₃) solutions. ZnO were etched at various times and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy to allow the examination of their structural and optical properties. The XRD results revealed that the intensity of ZnO(002) decreased when the thin films were etched in varying HNO₃ concentrations over different periods of time. The above observation is attributed to the dissolution of the ZnO(002). The SEM images showed that the thickness of the ZnO layers decreased over the etching time, which resulted from the isotropic etching by the HNO₃ solution. The PL emission intensity initially increased with increasing etching time. However, with further etching of the samples, the PL spectra showed a decreasing trend in intensity as a result of the decrease in the surface-to-volume ratio. All results lead to the conclusion that 1.0% HNO₃ has the capability to change the ZnO surface significantly.

Keywords: Photoluminescence spectroscopy; scanning electron microscope; wet chemical etching; X-ray diffraction; zinc oxide

ABSTRAK

Penyelidikan ini melaporkan fabrikasi struktur zink oksida berliang melalui proses punaran basah. Filem nipis ZnO dienapkan ke atas substrat silikon (111). Larutan pemunar yang digunakan dalam kajian ini adalah larutan asid nitrik (HNO₃) yang berkepekatan 0.1% dan 1.0%. Filem nipis ZnO dipunarkan selama beberapa jangka waktu yang ditetapkan dan ciri-ciri struktur dan optik dikaji dengan menggunakan pembelauan sinar-X (XRD), mikroskop elektron imbasan (SEM) dan spektroskopi fotoluminesens (PL). Keputusan XRD menunjukkan bahawa keamatan bagi puncak ZnO(002) menurun selepas filem nipis ZnO dipunarkan dalam larutan yang berkepekatan berlainan untuk jangka waktu yang berlainan. Pemerhatian ini adalah disebabkan penguraian ZnO(002) semasa proses punaran filem nipis. Imej-imej daripada SEM pula menunjukkan ketebalan filem nipis ZnO berkurangan dengan peningkatan masa punaran. Pemerhatian ini adalah disebabkan proses punaran isotropik oleh larutan HNO₃. Manakala spektrum PL pada peringkat awal punaran menunjukkan peningkatan keamatan puncak apabila masa punaran meningkat. Namun begitu, proses punaran yang berterusan menunjukkan keamatan puncak PL mula menunjukkan trend menurun dan fenomena ini adalah disebabkan penurunan nisbah luas permukaan terhadap isi padu dalam filem nipis ZnO.

Kata kunci: Mikroskop elektron pengimbas; pembelauan sinar-X; punaran basah; spektroskopi fotoluminesen, zink oksida

REFERENCES

Ang, C.I., Lu, Leonard, Ooi, P.K., Yaakob, S., Ching, C.G., Ng, S.S., Hassan, Z., Abu Hassan, H. & Abdullah, M.J. 2011. Fabrication of porous ZnO thin films using wet chemical etching with 0.5% HNO3. Microelectronics International 29: 96-100.

Basu, P.K., Saha, N., Maji, S., Saha, H. & Basu, S. 2008. Nanoporous ZnO thin films deposited by electrochemical anodization: Effect of UV light. Journal of Material Science: Materials in Electronics 19: 493-499.

Chang, J.Y., Kim, T.G. & Sung, Y.M. 2011. Synergistic effects of SPR and FRET on the photoluminescence of ZnO nanorod heterostructures. Nanotechnology 22: 425708.

Dubey, R.S. & Gautam, D.K. 2009. Synthesis and characterization of nanocrystalline porous silicon layer for solar cells applications. Journal of Optoelectronic and Biomedical Materials 30: 8-14.

Kim, S.J., Kang, H.G. & Choi, J. 2010. Surfactant-free preparation of ZnO dendritic structures by electrochemical method. Current Applied Physics 10: 740-743.

Ozgur, U., Alivov, Y.I., Liu, C., Teke, A., Reshchikov, M.A., Dogan, S., Avrutin, V., Cho, S.J. & Morkoc, H.J. 2005. A comprehensive review of ZnO materials and devices. Journal of Applied Physics 98: 041301.

Shao, J.F., Parera, A.G.U., Jayaweera, P.V.V. & He, D.Y. 2010. Low-cost UV-IR dual band detector using nonporous ZnO film sensitized by PbS quantum dot. Chinese Physics Letters 27: 027302.

Sharma, P., Mansingh, A. & Sreenivas, K. 2002. Ultraviolet photoresponse of porous ZnO thin films prepared by unbalanced magnetron sputtering. Applied Physics Letter 80: 553-555.

Shim, E.S., Kang, H.S., Kang, J.S., Kim, J.H. & Lee, S.Y. 2002. Effect of the variation of film thickness on the structural and optical properties of ZnO thin films deposited on sapphire substrate using PLD. Applied Surface Science 186: 474-476.

Sood, A.K., Zhong, L.W., Polla, D.L., Dhar, N.K., Manzur, T. & Anwar, A.F.M. 2011. ZnO nanostructures for optoelectronic applications. In Optoelectronics Devices and Properties, edited by Sergiyenko, O. Croatia: In-Tech.

Sumida, T., Wada, Y., Kitamura, T. & Yanagida, S. 2001. Macroporous ZnO films electrochemically prepared by templating of opal films. Chemistry Letters 30: 38-39.

Yi, G.C., Wang, C. & Park, W.I. 2005. ZnO nanorods: Synthesis, characterization and applications. Semiconductor Science and Technology 20: S22-S34.

Yoo, D.G., Nam, S.H., Kim, M.H., Jeong, S.H., Jee, H.G., Lee, H.J., Lee, N.E., Hong, B.Y., Kim, Y.J., Jung, D. & Boo, J.H. 2008. Fabrication of the ZnO thin films using wet-chemical etching processes on application for organic light emitting diode (OLED) devices. Surface Coating Technology 20: 5476-5479.

Zhao, Z., Lei, W., Zhang, X., Wang, B. & Jiang, H. 2010. ZnO-based amperometric enzyme biosensors. Sensors 10: 1216-1231.

Zhao, L., Liu, C., Teng, X., Sun, S., Zhang, W., Zhu, J., Feng, Y. & Guo, B. 2006. The surface topography of GaN grown on Si (1 1 1) substrate before and after wet chemical etching. Material Science in Semiconductor Processing 9: 403-406.

*Corresponding author; email: chingchinguan@gmail.com