Site‐specific excitation of Eu ions in GaN

Abstract

We performed cathodoluminescence (CL) studies on Eu‐doped GaN layers that were grown using the Interrupted Growth Epitaxy (IGE) method. We compare these results with our site‐selective combined excitation‐emission spectroscopy (CEES) studies in which numerous Eu3+ incorporation sites can be identified unambiguously. We find that for high beam currents the emission intensity saturates in a way that can only be accounted for by a coexistence of at least two different excitation processes. The ratio in excitation efficiency between these two processes is about 5. This conclusion is supported by the CL spectra which show less pronounced saturation for the majority substitutional incorporation site compared to the defect trap‐related (most likely interstitial) site. We further find that only a small fixed portion of the majority site can be excited through electron bombardment. We explain this behavior with a model for the excitation process in which defects are involved as an intermediate trap of excitation. Energy transfer can occur only to those substitutional Eu ions that are in close proximity to the trap. In the case that the Eu ion defect constitutes the trap itself, the spectra are clearly distinguishable and the transfer rates are highest. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)