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

Effect of Dislocations on Local Transconductance in AlGaN/GaN Heterostructures as Imaged by Scanning Gate Microscopy. J.W.P.Hsu, N.G.Weimann, M.J.Manfra, K.W.West, D.V.Lang, F.F.Schrey, O.Mitrofanov, R.J.Molnar: Applied Physics Letters, 2003, 83[22], 4559-61