Effect of internal absorption on cathodoluminescence from GaN
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Effect of internal absorption on cathodoluminescence from GaN Klaus Knobloch, Piotr Perlin, Joachim Krueger, Eicke R. Weber and Christian Kisielowski MRS Internet Journal of Nitride Semiconductor Research / Volume 3 / January 1998 DOI: 10.1557/S1092578300000764, Published online: 13 June 2014
Link to this article: http://journals.cambridge.org/abstract_S1092578300000764 How to cite this article: Klaus Knobloch, Piotr Perlin, Joachim Krueger, Eicke R. Weber and Christian Kisielowski (1998). Effect of internal absorption on cathodoluminescence from GaN . MRS Internet Journal of Nitride Semiconductor Research, 3, pp e4 doi:10.1557/S1092578300000764 Request Permissions : Click here
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MRS
Internet Journal Nitride Semiconductor Research
Effect of internal absorption on cathodoluminescence from GaN Klaus Knobloch1, Piotr Perlin 1, Joachim Krueger1, Eicke R. Weber 1 and Christian Kisielowski2 1University 2NCEM,
of California at Berkeley, Department of Materials Science and Mineral Engineering, Lawrence Berkeley Laboratory,
(Received Tuesday, January 27, 1998; accepted Tuesday, February 24, 1998)
We have studied optical properties of GaN grown on sapphire by metalorganic chemical vapor deposition in the near band-edge energy range by cathodoluminescence. A large shift of the bandedge luminescence to lower energies is induced by increasing the beam energy. The free exciton position shifts about 20 meV when the beam energy is increased from 5 keV to 25 keV at roomtemperature. The effect is explained by internal absorption caused by an exponential absorption tail at the band-edge. An Urbach parameter of about 30 to 40 meV for the exponential band-tail in our samples is estimated by comparing experimental with simulated spectra.
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Introduction
Luminescence methods, photoluminescence (PL) and cathodoluminescence (CL), are widely used to study the optical properties of GaN and other wide band-gap III-V nitrides. In particular strain [1] [2], composition [3] [4] and electric fields [5] [6] have been studied by the analysis of the excitonic transitions. The advantage of CL is the spatial resolution of this SEM based method and its applicability to materials with band-gap energies greater than those accessible by laser excitation. When studying GaN by CL in the near-band-edge photon energy range we observed a strong peak shift to lower photon energies when the beam energy is increased (Figure 1). This effect had been observed before [7]. The authors speculated that it was caused by strain relaxation and/or piezoelectric fields. In contrast, it is the purpose of this letter to show that the effect can be explained by internal absorption of the luminescent light. A peak shift may be observed which increases with higher beam energies, and hence greater penetration depth, beca
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