Strong room temperature 510 nm emission from cubic InGaN/GaN multiple quantum wells
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Strong room temperature 510 nm emission from cubic InGaN/GaN multiple quantum wells S.F. Li1, D.J. As1, K. Lischka1, D.G. Pacheco-Salazar2, L.M.R. Scolfaro2, J.R. Leite2,*, F. Cerdeira3, E.A. Meneses3; 1 University of Paderborn, Department of Physics, Warburger Str. 100, D-33098 Paderborn, Germany; 2 Institute of Physics, University of Sao Paulo, P.O. Box 66318, Sao Paulo-SP, Brazil; 3 Institute of Physics Gleb Wataghin, University of Campinas, P.O. Box 6165, Campinas-SP, Brazil ABSTRACT Cubic InGaN/GaN double heterostructures and multi-quantum-wells have been grown by Molecular Beam Epitaxy on cubic 3C-SiC. We find that the room temperature photoluminescence spectra of our samples has two emission peaks at 2.4 eV and 2.6 eV, respectively. The intensity of the 2.6 eV decreases and that of the 2.4 eV peak increases when the In mol ratio is varied between x = 0.04 and 0.16. However, for all samples the peak energy is far below the bandgap energy measured by photoluminescence excitation spectra, revealing a large Stokes-like shift of the InGaN emission. The temperature variation of the photoluminescence intensity yields an activation energy of 21 meV of the 2.6 eV emission and 67 meV of the 2.4 eV emission, respectively. The room temperature photoluminescence of fully strained multi quantum wells (x = 0.16) is a single line with a peak wavelength at about 510 nm.
INTRODUCTION Low cost short-haul communications systems using polymethyl methacrylate (PMMA) plastic optical fibers (POFs) require inexpensive light sources emitting around the PMMA absorption minimum at 510 nm (around 70 dB/km). For the realization of these devices group III-nitride wide-band-gap semiconductors are the material of choice. Due to their large direct band gap they are well suited for a wide range of applications, e.g. as light emitter in the green to ultraviolet range or as detectors [1]. Group III-nitrides can be produced in the thermodynamic stable configuration with hexagonal (wurtzite) crystal structure and in a metastable modification with cubic (zincblende) structure. The main difference between these two modifications is the absence of piezoelectric and spontaneous polarization fields in the cubic modification. Today high-efficiency LEDs which have InGaN/GaN quantum wells in the active zones are produced in large quantities. However, these quantum wells, which are mainly grown in a (0001) growth direction, have *
deceased
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strong built-in electric fields due to the piezoelectric effect and spontaneous polarization. For that reason only nm-wide quantum wells yield large radiative recombination efficiency. Due to the higher symmetries polarization fields are absent in cubic III-nitrides [2]. Furthermore, due to the slightly smaller energy gap of the cubic nitrides (200meV lower than the hexagonal counterpart), smaller mol fractions of In in the well of InGaN/GaN quantum wells are necessary to reach emission wavelengths beyond 510 nm. Therefore, group III-nitrides seem to be the material choice for the realization of res
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