Mapping optical properties of distinct dislocations in GaN based electronic devices

Abstract

GaN exhibits excellent electronic properties for high power electronic devices, but it cannot be manufactured free of lattice defects. For electronic devices reliability and expected lifetime are crucial parameters driven by the density of distinct types of these dislocations. Consequently, it is important to understand how which type of lattice defect influences the overall performance and how the types of lattice defects can be characterized on an industrial scale. Typically, the defect density is in the range of 6 billion per cm , but only a fraction of them is critically.2 In the present work we investigate electrically characterized dislocations by using low voltage valence electron energy loss spectrometry (LV-VEELS) and cathodoluminescence (CL). Using low beam energies prevents the sample from beam damage and avoids relativistic effects altering both, the VEELS and the CL spectrum, respectively. The electrical characterization was done by means of electron beam induced current (EBIC) and electron channelling contrast imaging (ECCI), both using a scanning electron microscope (SEM), prior to sample preparation employing focused ion beam (FIB). Electrically active defects show a significant yellow band emission at ~2eV, both in VEELS and CL. The reason for this is found in gap states due to enrichment of impurity atoms in the affected dislocations. For this purpose, chemical analysis was also performed using 200 keV EELS.