Surface electrical characterization of defect related inhomogeneities of AlGaN/GaN/Si heterostructures using scanning capacitance microscopy

摘要

Large mismatch of lattice constants and thermal expansion coefficients between materials in AlGaN/GaN/Si heterostructures lead to high density of structural defects and material inhomogeneities in the epitaxial layers. The influence of growth conditions on the local electronic properties of the fabricated AlGaN/GaN/Si heterostructures was investigated using scanning capacitance microscopy (SCM). The significant differences of spatial electronic properties in the nanometer scale for the heterostructures grown with and without application of SiN nanomasking layer were revealed. Analysis of two dimensional images of the SCM signal and dC/dV(Amp) = f(V-DC) spectrum allowed to conclude that negative charge accumulated at dislocations in the epitaxial layers could affect the surface electronic states of the AlGaN barrier layer but could not have major impact on the two dimensional electron gas formation at the AlGaN/GaN interface.