AVS 52nd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuA

Paper EM-TuA5
Direct Formation of Nanoporous ZnO Networks by MBE

Tuesday, November 1, 2005, 3:20 pm, Room 309

Session: Growth and Characterization of ZnO
Presenter: S.M. Durbin, University of Canterbury, New Zealand
Authors: S.M. Durbin, University of Canterbury, New Zealand
W.C.T. Lee, University of Canterbury, New Zealand
R.P. Millane, University of Canterbury, New Zealand
R.J. Reeves, University of Canterbury, New Zealand
Z. Liu, University of Sydney, Australia
S. Ringer, University of Sydney, Australia
F. Bertram, Otto-von-Guericke-University Magdeburg, Germany
Correspondent: Click to Email
Porous semiconductors have captured significant attention in the past decade, both as a result of visible luminescence from silicon structures and due to the potential for creating surface-active devices such as gas sensors. Porous networks of these materials are generally formed in conjunction with some form of anodic etching procedure, although some arc processing has been reported as well. In contrast, we have observed the direct formation of large-scale multi-level nanoporous ZnO networks grown using an RF plasma-assisted molecular beam epitaxy (RF-PAMBE) technique without the need for etching or other postprocessing. Elemental Zn was evaporated using a standard effusion cell, and active oxygen was supplied using an Oxford MDP21 plasma source with alumina components in the plasma chamber. In-situ reflection high-energy electron diffraction exhibited patterns consistent with c-axis oriented single crystal growth on the GaN/sapphire template. Initial estimates indicate a porosity of at least 20% based on analysis of field emission scanning electron microscopy images, which also show feature sizes on the order of tens of nanometres and pores of approximately 100 nm in diameter. Cross-sectional transmission electron microscopy confirms the presence of a porous network on top of a 20 nm thick continuous ZnO layer. Low temperature photoluminescence reveals a broad feature near the bandedge of ZnO, which is near the short wavelength limit of the measurement apparatus. The driving mechanism underlying the formation of the nanoporous layer is unclear, but may be related to preferentially-oriented surface features formed on the GaN buffer layer. This work is supported in part by the MacDiarmid Institute for Advanced Materials and Nanotechnology, and the University of Canterbury.