Yellow Luminescence Imaging of Epitaxial Lateral Overgrown GaN Using Ionoluminescence
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Yellow Luminescence Imaging Of Epitaxial Lateral Overgrown GaN Using Ionoluminescence E. J. Teo1, A A. Bettiol1, T. Osipowicz1, M.S. Hao2, S.J. Chua2, Y. Y. Liu3 1 Research Centre for Nuclear Microscopy, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 2 Institute of Materials Research and Engineering, National University of Singapore, Singapore 119260 3 Centre for Integrated Circuit Failure Analysis and Reliability, Dept of Electrical and Electronic Engineering, National University of Singapore, Singapore 119260 ABSTRACT Luminescence imaging techniques such as Photoluminescence (PL) and Cathodoluminescence (CL) have been extensively used to characterize the optical properties of GaN. However, analysis using these techniques is limited to near surface regions and may not represent bulk material properties. This restricts the understanding of the defect-related yellow luminescence in GaN, which tends to originate at the interface region. In this work, we propose the use of MeV protons to probe several microns into a Epitaxial Lateral Overgrown GaN layer. Monte Carlo simulations of the ionization profile show that MeV ions have a much higher penetration depth than the keV electrons used in CL. The well-defined electronic energy loss peak or ‘Bragg peak’ at the end of range for MeV ions enables us to perform depth resolved imaging of the yellow luminescence distribution. Another advantage of using a MeV ion beam over keV electrons is the relatively small lateral spreading of ions in a material, making it a more suitable technique for providing high-resolution images of any buried defects in GaN.
INTRODUCTION The luminescence properties of GaN have been studied extensively due to its application in optoelectronic devices. In addition to the near band edge emission, a defect-related yellow band is often observed in as-grown GaN deposited by various methods. Many groups have performed CL measurements to investigate the correlation of yellow luminescence (YL) with extended defects [1,2]. However, these studies are limited to near surface regions due to the relatively small probing depth of the keV electrons used in CL, and do not necessarily represent bulk properties. The yellow intensity and distribution is expected to be vastly different with depth since the dislocations and extended defects are generated as a consequence of the lattice mismatch between the layer and the substrate. There have also been some studies using cross sectional CL to reveal features not detectable in the planar view [3]. In order to study the effects of defects on luminescence at various depths in GaN, we introduce a new technique called Ionoluminescence (IL) to characterize GaN. In this work, energetic MeV H+ ions are employed to investigate several microns into epitaxial lateral overgrown (ELO) GaN layer. The spatial distribution of the threading dislocations in ELO GaN also allows for the investigation of the correlation of threading dislocations with YL. Different depths are probed by vary
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