The impact of electron beam damage on the detection of indium-rich localisation centres in InGaN quantum wells using transmission electron microscopy

High-resolution transmission electron microscope (HRTEM) lattice fringe images and lattice parameter maps are used to reveal the rapid modification of InGaN quantum wells by the electron beam in a TEM. Images acquired within seconds of first irradiating a region of quantum well do not exhibit the strong nanometre-scale strain contrast which has been reported to signify the presence of very indium-rich regions in InGaN quantum wells. However, after a very short period of irradiation by a relatively low electron beam current density, images of the specimen could be interpreted as indicating the presence of these indium "clusters" The beam damage is shown to occur for the InGaN quantum wells grown in our lab as well as those in a commercial blue light emitting diode (LED) and in TEM specimens prepared only using mechanical polishing. Possible mechanisms for the beam damage are discussed and we make suggestions as to what may cause exciton localisation in quantum wells that do not contain gross composition fluctuations.