Characterization of AlxGa1-xAs/GaAs heterojunction bipolar transistor structures using cross-sectional scanning force microscopy

We have characterized base-layer width and dopant distributions on cleaved cross-sections of AlxGa1-xAs/GaAs heterojunction bipolar transistor (HBT) s tructures using a variation of electrostatic force microscopy. The contrast observed is sensitive to the local dopant concentration through variations in the depletion layer depth extending into the sample surface, and enable s delineation of individual device regions within the epitaxial layer struc ture with nanoscale spatial resolution. In two epitaxially grown HBT struct ures, one with 50 nm base width and the other with 120 nm base width, we ar e able to delineate clearly the emitter, base, collector, and subcollector regions, and to distinguish regions within the collector differing in dopan t concentration by a factor of two. We have also distinguished clearly betw een the base widths in these samples and have precisely measured the differ ence to be 63 +/- 3 nm, in excellent agreement with the nominal difference of 70 +/- 7 nm. (C) 2000 American Institute of Physics. [S0021-8979(00)0080 4-5].