Correlating Structural and Electrical Characteristics of Threading Dislocations in GaN -on- Si Heterostructures and p - n Diodes by Multiple Microscopy Techniques

Abstract

Structural and electrical properties of a- and a + c-type threading dislocations in metal-organic vapor-phase epitaxy-grown $\mathrm{Si}$-doped $\mathrm{Ga}\mathrm{N}$ (0001) are determined by combining multiple scanning probe microscopy approaches. The analysis examines the space-charge region (SCR) formed around dislocation cores and clarifies the role it plays in influencing the local recombination, the surface-potential characteristic, and even the conductivity. Direct evidence of the SCR is obtained from a differential capacitance (dC/dV) measurement at dislocation sites on the (0001) surface. Experimental dC/dV (V) measurement results supported by technology computer-aided design calculations of capacitance, accounting for the theoretical deep levels related to different atom-core structures of the identified dislocations, reveal quantitative differences in their respective trap densities. This study is extended to p-n $\mathrm{Ga}\mathrm{N}$ vertical diodes to analyze the doping distribution across active layers. Through a correlated cross-section investigation combining electron-channeling contrast-imaging microscopy, the underlying dislocations within the depth limited by the screening of their SCRs are found to severely impact the homogeneity of the cross-section dC/dV contrast in the low-doped n-type drift layer of the diodes. This raises serious concerns regarding any quantification efforts by differential capacitance measurements in $\mathrm{Ga}\mathrm{N}$ on $\mathrm{Si}$, where the dislocation density is in the order of ${10}^{9}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$.