Luminescence And Structural Properties Of InGaN Epilayer, Quantum Well And Quantum Dot Samples Using Synchrotron Excitat
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Luminescence And Structural Properties Of InGaN Epilayer, Quantum Well And Quantum Dot Samples Using Synchrotron Excitation K.P. O’Donnell1, R.W. Martin1, M.E. White1, M.J. Tobin2, J.F.W. Mosselmans2, I.M. Watson3, B. Damilano4 and N. Grandjean4. 1
Dept of Physics and Applied Physics, Strathclyde University, Glasgow G4 0NG, Scotland, UK.
2
CLRC Daresbury Laboratories, Warrington, WA4 4AD, England, UK.
3 4
Institute of Photonics, Strathclyde University, Glasgow G4 0NW, Scotland, UK. CRHEA/CNRS, Valbonne, France.
ABSTRACT The Daresbury synchrotron radiation source (SRS) provides bright, tunable x-rays for scattering and absorption probes of local structure. Scanning confocal microscopy and luminescence decay measurements employ the SRS in alternative ways, as a tunable luminescence excitation engine and as a source of weak, 160 ps pulses with a large pulse-topulse separation, respectively. This report first describes local atomic structure studies of InGaN epilayers by extended x-ray absorption fine structure (EXAFS). In addition, we report photoluminescence (PL) imaging, PL microspectroscopy and photoluminescence decay studies of various nitride samples, including tailored InGaN quantum wells and discs. INTRODUCTION The use of synchrotron radiation for structural studies of solids is a cornerstone of materials research. Synchrotrons are sources of extremely bright, tunable x-ray radiation. When applied to semiconductors, the high brightness of synchrotron sources permits measurements on time scales that are short compared to crystal growth times, so that, for example, in-situ measurements of atomic-structural parameters can be made via x-ray diffraction. After growth, a very complete study of sample crystallinity can be made using reciprocal space mapping. The full range of structural x-ray techniques is described on the Daresbury Laboratories website [1]. Synchrotrons also produce appreciable amounts of near-visible light, tunable in wavelength ranges that are at present inaccessible to lasers. Ultraviolet light can excite fluorescence in widegap semiconductors. In the microscope SYCLOPS (SYnchrotron ConfocaL OPtical Scanning), synchrotron excitation is used in a scanning confocal microscope to produce images that have enhanced resolution in both lateral and vertical directions [2]. Synchrotrons are intrinsically pulsed sources, but the repetition rate in so-called ‘multibunch’ operation is very high. If all but one of the electron bunches that circulate in the storage ring is suppressed, the synchrotron, in ‘single-bunch’ mode, operates as a pulsed source with a rather low mark/space ratio (160 ps pulses, 3 MHz repetition rate). Such a source is ideal for measuring long-tailed luminescence decay profiles in solids [3]. The present work aims to apply all of the synchrotron-based techniques mentioned above to various structures containing InGaN. G9.11.1
SAMPLE DETAILS AND EXPERIMENTAL TECHNIQUES We wish to relate PL spectra of InGaN nanostructures to the local structure derived from EXAFS modelling, and also
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