We describe a technique based on photoelectrochemical wet etching that enables efficient and accurate evaluation of dislocation densities in n-type GaN films. The etching process utilizes dilute aqueous KOH solutions and Hg arc lamp illumination to produce etched GaN "whiskers'' by selectively etching away material around threading dislocations. The etched whiskers, each corresponding to a single threading dislocation, can be effectively imaged by plan-view scanning electron microscopy. The distribution and density of dislocations are then readily observed over very large sample areas. Transmission electron microscope and atomic force microscope studies of the GaN samples confirm the accuracy of the dislocation density obtained by the wet etching. (C) 1999 American Institute of Physics. [S0003-6951(99)04416-2].
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