Effect of dislocations on local transconductance in AlGaN/GaN heterostructures as imaged by scanning gate microscopy

The spatial variations of transconductance in AlGaN/GaN heterostructures were mapped using a conducting tip atomic force microscope. The conducting tip locally modulates the two-dimensional electron gas (2DEG) while the change in the drain current was monitored as a function of tip position. A spatial resolution of 250 nm was obtained. This technique enables us to investigate the role of defects in transistor performance. In particular, when biased near the depletion of the 2DEG, the transconductance map displays a cell structure, with low signal regions correlating with the positions of negatively charged threading dislocations.