Nanoscale electrical conductance and leakage currents in etched and selective-area regrown GaAs pn junctions

Abstract

Analysis and mitigation of junction leakage currents are central to the engineering of vertical semiconductor diode structures. We have used scanning capacitance microscopy and conductive atomic force microscopy to characterize, with nanoscale spatial resolution, charge carrier distributions and local current distributions at the edges of mesa-etched and selective-area regrown vertical GaAs pn junction diodes grown by molecular-beam epitaxy. These studies indicate that wet etch-induced defect states are present on the etched surfaces of mesa structures, leading to increased local electrical conductivity that could contribute to sidewall leakage. For selective-area regrown structures, we observe an annular low-conductivity region in the vicinity of the GaAs–SiO2 interface at the edge of regrown pn junction structures that could act to suppress current flow at the edges of pn junction diodes fabricated from selective-area regrown material. Together, these studies provide new insights into the origin of sidewall leakage currents in mesa-etched GaAs pn junction diodes and their suppression in selective-area regrown devices.