Direct imaging of a biased p-n junction with conductance mapping

We report characterization of Si p-n junction arrays using simultaneous conductance imaging and constant current mode (topographical) scanning tunneling microscopy imaging over a range of reverse bias conditions. Both constant current and conductance imaging of the electrically different regions (n, p, and inverted region) show a pronounced dependence on applied p-n junction bias. Tunneling spectra measured across the p-n junction show that the conductance contrast agrees well with the expected variation due to tip-induced band bending. Taken in combination with the topographical image, conductance images can be used to characterize spatial variations of carrier densities across the device.