Threshold voltage mapping at the nanoscale of GaN-based high electron mobility transistor structures using hyperspectral scanning capacitance microscopy

Abstract

Hyperspectral scanning capacitance microscopy (SCM) measures dC/dV−V spectra at every XY location of a semiconductor sample surface area. We report its application to GaN-based high electron mobility transistor (HEMT) structures to map threshold voltage (Vth) at the nanoscale. The consistency between the conventional SCM data and the hyperspectral SCM data set of the same area on the HEMT surface provides evidence for the reliability of hyperspectral SCM. We developed a method to extract a map of Vth distribution across the surface of the HEMT structure at the nanoscale from the hyperspectral SCM data set. The map reveals that most of the fissures (i.e., enlarged pits formed at threading dislocation surface endings) on the nitride sample surface reduce local Vth. Other variations in Vth in regions free of the fissures could be a result of thickness and/or composition inhomogeneities in the AlxGa1−xN barrier layer. Conventional SCM and other techniques cannot provide these detailed insights obtained through hyperspectral SCM.