2 March 2006 Two different features of ZnO: transparent ZnO:Ga electrodes for InGaN-LEDs and homoepitaxial ZnO films for UV-LEDs
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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.
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K. Nakahara, K. Nakahara, H. Yuji, H. Yuji, K. Tamura, K. Tamura, S. Akasaka, S. Akasaka, H. Tampo, H. Tampo, S. Niki, S. Niki, A. Tsukazaki, A. Tsukazaki, A. Ohtomo, A. Ohtomo, M. Kawasaki, M. Kawasaki, } "Two different features of ZnO: transparent ZnO:Ga electrodes for InGaN-LEDs and homoepitaxial ZnO films for UV-LEDs", Proc. SPIE 6122, Zinc Oxide Materials and Devices, 61220N (2 March 2006); doi: 10.1117/12.660552; https://doi.org/10.1117/12.660552
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