Channeling contrast microscopy of GaN and InGaN thin films

Abstract

The recent development of blue and green light emitting diodes (LED) based on single quantum well structures made from GaN and related materials (AlGaN, InGaN) has created many efforts to achieve a complete characterisation of devices grown under various conditions. Here we report on CCM measurements on GaN thin films (d=0.7–3.0 μm) grown by metal organic vapour phase epitaxy (MOVPE) and on 500 Å InGaN films grown epitaxially on top of the GaN thin films. The samples were analysed by broad beam channeling and channeling contrast microscopy (CCM), using 1–2 MeV H+ and He+ ions. Generally, very low minimum yields were found (χmin=2–4%), indicating nearly perfect crystal structures. The susceptibility to ion–beam induced damage was assessed by random and channeled 1 MeV He+ irradiation and subsequent CCM analysis. CCM also revealed the presence μm-sized regions in the InGaN films with increased In signal strength. The channeling PIXE data for 500 Å thin films are found to be in excellent agreement with the corresponding RBS results, allowing the determination of channeling yields of elements for which RBS data is difficult to obtain.