InGaN Layers Grown on Al2O3/ZnO Substrates Prepared by Atomic Layer Deposition
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1035-L11-23
InGaN Layers Grown on Al2O3/ZnO Substrates Prepared by Atomic Layer Deposition Nola Li1, Shen-Jie Wang1, Jeff Nause2, Adriana Valencia2, Christopher Summers3, and Ian Ferguson1 1 Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr., Atlanta, GA, 30332 2 Cermet Inc., Atlanta, GA, 30318 3 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, 30332 ABSTRACT Atomic layer deposition (ALD) of Al2O3 is used as a transition layer on ZnO substrates before III-Nitride growth by metalorganic chemical vapor deposition (MOCVD). This transition layer is being used to minimize Zn diffusion from the substrate, protect the ZnO surface from H2 back etching, and promote high quality nitride growth. ALD-Al2O3 films were grown at 100oC and then annealed in a furnace at various times at 1100oC for crystallization of the transition layer. XRD results showed both Al2O3 and ZnAl2O4 phases at different intensities for 20 and 50nm ALD-Al2O3 films. In addition, high indium concentration InGaN layers have been successfully grown on the Al2O3/ZnO substrate. This work shows that a short annealing time for the ALD-Al2O3 layer will be optimal for InGaN growth. INTRODUCTION ZnO is a wurtzite semiconductor with a small c-plane lattice mismatch of 1.8% compared to wurtzite GaN. InGaN, with a composition of ~21% indium, possesses a perfect lattice-match with ZnO in the a-axis direction according to Vegard’s law and hence allows for the possible growth of InGaN layers without misfit dislocations [1, 2]. ZnO also has a similar thermal expansion coefficient with GaN which allows for almost zero thermal strain [3]. In addition, ZnO substrates are conductive so can be utilized in vertical structures allowing for multiple electrodes to be formed on both surfaces to improve current spreading [4, 5]. Furthermore, ZnO can be wet-etched chemically and easily removed to allow for thin GaN device structures [6, 7]. Therefore, ZnO is an ideal alternative substrate for GaN and InGaN based devices compared to growth on sapphire or SiC. Metalorganic chemical vapor deposition (MOCVD) is currently the dominant growth technology for GaN-based materials and devices, and there is a need to explore this growth technique for ZnO substrates. It is well known that the decomposition of ZnO substrates leads to an increase in Zn and O diffusion during high temperature growth, which can result in poor epitaxial growth and degrade the film quality [8, 9]. Commercial MOCVD usually grow over 1000oC for GaN on sapphire substrates, which makes MOCVD growth of GaN and InGaN on ZnO substrates difficult. Moreover, H2 is widely used as a carrier gas for GaN based epilayers grown on sapphire during MOCVD growth. NH3 as the common nitrogen source also contributes H2 during growth especially at high temperature. These H2 sources etch the ZnO surface prior to growth [10]. In this work, atomic layer deposition (ALD) is used to provide an Al2O3 transition layer on ZnO substrates before nitride growth by MOCVD in order to p
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