Electron channelling contrast imaging (ECCI) is a powerful technique for revealing and identifying threading dislocations in nitride semiconductor thin films. In ECCI, changes in crystallographic orientation or changes in lattice constant due to strain are revealed by monitoring the intensity of backscattered electrons as an electron beam is scanned over a suitably oriented sample. Extremely small orientation changes are detectable, enabling dislocations to be imaged [1, 2]. Cathodoluminescence (CL), the emission of light when a material is bombarded by an electron beam, is well established as a spectroscopic characterisation tool in the studyof light-emitting semiconductors. When measured in the hyperspectral imaging mode, CL can be used to obtain both spectrally and spatially resolved luminescence properties of materials and may be used to map composition, strain, defects and doping in a sample . Dislocations which give rise to non-radiative recombination are observed as black spots in a CL image. By comparing an ECC image with a CL image from exactly the same micron-scale region of a sample, we may directly observe the influence of individual dislocations on light emission. In this work, we will describe the use of electron channelling contrast imaging (ECCI) in a field emission scanning electron microscope to reveal and identify defects in nitride semiconductor thin films, and CL hyperspectral imaging to study their optical properties. Preliminary results on the effect of doping and the type of dopants on structural and optical properties of GaN thin films grown by metal organic vapour phase epitaxy (MOVPE) will be discussed.
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