Near Field Optical Spectroscopy of GaN/AIN Quantum Dots
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Near Field Optical Spectroscopy of GaN/AlN Quantum Dots 1
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A. Neogi1, B. P. Gorman , H. Morkoç , T. Kawazoe , M. Ohtsu , M. Kuball 1
Department of Physics and Materials Engineering, University of North Texas, Denton, TX, USA. 2 Department of Electrical Eng.,Virginia Commonwealth University, Richmond, VA, USA. 3 Department of Electrical Engineering, University of Tokyo, Japan 4 Department of Electrical Engineering, University of Bristol, U.K.
ABSTRACT We investigate the spatial distribution and emission properties of self-assembled GaN/AlN quantum dots. High-resolution transmission electron microscopy reveals near vertical correlation among the GaN dots due to a sufficiently thin AlN spacer layer thickness, which allows strain induced stacking. Scanning electron and atomic force microscopy show lateral coupling due to a surface roughness of ~ 50-60 nm. Near-field photoluminescence in the illumination mode (both spatially and spectrally resolved) at 10 K revealed emission from individual dots, which exhibits size distribution of GaN dots from localized sites in the stacked nanostructure. Strong spatial localization of the excitons is observed in GaN quantum dots formed at the tip of self-assembled hexagonal pyramid shapes with six [ 10 1 1 ] facets. INTRODUCTION The shrinking of optical devices and systems to the nanoscale limit is essential for the optoelectronics industry, and depends critically on achieving sub-wavelength coupling and operation[1-10]. Scaling down optoelectronic devices to nanometric dimensions and their integration in photonic circuits requires novel approaches to light manipulation. Nanophotonic emitters operating in the near-field optical wavelength range capable of performing beyond the diffraction limit are an essential component of integrated photonic circuits [1, 6, 8]. Current progress in nanotechnology is based on novel quantum electronic devices as quantum wells, quantum dots, single-electron transistors, etc. The characterization of the optical properties of nanophotonic emitters such as quantum dots using near-field optical spectroscopy is essential not only for the fabrication of nanophotonic emitters but also for understanding the fundamental emission mechanism in single quantum dots. The study of self-assembled GaN quantum dots presents a challenge, as the placement of individual dots is difficult to control during the epitaxial growth process, and the dot density can be quite high. Thus traditional experimental techniques often only 1
Corresponding Author: Email:[email protected]
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allow simultaneous observation of large ensembles of quantum dots where inhomogeneous broadening washes out many of the interesting features. We have investigated the optical properties of GaN QD and have observed that the built-in strain fields significantly influence the radiative recombination lifetime and thereby the emission properties of this system [4,5]. The role of size distribution of the QDs on the radiative emission process is not yet clear. MATERIAL GROWTH The sample
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