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Proceedings Paper

Two different features of ZnO: transparent ZnO:Ga electrodes for InGaN-LEDs and homoepitaxial ZnO films for UV-LEDs
Author(s): K. Nakahara; H. Yuji; K. Tamura; S. Akasaka; H. Tampo; S. Niki; A. Tsukazaki; A. Ohtomo; M. Kawasaki
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Paper Abstract

We have used molecular beam epitaxy (MBE) to deposit gallium (Ga) doped ZnO (ZnO:Ga) films. The as-deposited ZnO:Ga films have worked as ohmic contacts for the p-type GaN layers without any kinds of post annealing process. The as-deposited ZnO:Ga films on a-plane sapphire substrates have resistivities of 2-4×10-4 Ωcm, and over 80 % transparency in the near-UV and visible wavelength regions. The brightness of InGaN light-emitting diodes (LEDs) with ZnO:Ga p-contacts has doubled compared to LEDs with conventional Ni/Au semi-transparent p-contacts when measuring the brightness from right above the device surfaces. In addition, using MBE, we have grown homoepitaxial polar ZnO films on (000+1)-plane (+c-plane) ZnO substrates, and also grown non-polar ZnO films on (1-100)-plane (m-plane) and (11-20)-plane (a-plane) ZnO substrates. Growth temperatures have not affected nitrogen-doping levels for +c-axis oriented (Zn-polar) nitrogen doped ZnO (ZnO:N) films. The phenomena were quite different from that for (000-1)-axis (-c-axis) oriented (oxygen-polar) growth, where nitrogen concentrations in ZnO decrease with increasing growth temperatures. We have observed c-axis direction growth for both of m-axis and a-axis oriented films. Oxygen-rich growth conditions flatten surfaces for both m-axis and a-axis oriented films, and the surfaces of m-axis oriented ZnO films flatten with increasing growth temperatures. Nitrogen concentrations in m-axis oriented ZnO:N films have been independent on growth temperatures.

Paper Details

Date Published: 2 March 2006
PDF: 18 pages
Proc. SPIE 6122, Zinc Oxide Materials and Devices, 61220N (2 March 2006); doi: 10.1117/12.660552
Show Author Affiliations
K. Nakahara, ROHM Co., Ltd. (Japan)
H. Yuji, ROHM Co., Ltd. (Japan)
K. Tamura, ROHM Co., Ltd. (Japan)
S. Akasaka, ROHM Co., Ltd. (Japan)
H. Tampo, National Institute of Advanced Industrial Science and Technology (Japan)
S. Niki, National Institute of Advanced Industrial Science and Technology (Japan)
A. Tsukazaki, Tohoku Univ. (Japan)
A. Ohtomo, Tohoku Univ. (Japan)
M. Kawasaki, Tohoku Univ. (Japan)

Published in SPIE Proceedings Vol. 6122:
Zinc Oxide Materials and Devices
Ferechteh Hosseini Teherani; Cole W. Litton, Editor(s)

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