Nanoscale Stress Localization Effects on the Radiation Susceptibility of GaN High-Mobility Transistors

Nanoscale localized mechanical stress fields develop unavoidably in microelectronic devices due to structural and processing aspects. Their global average is too small to influence bandgap or mobility, but it is proposed that stress localization can influence defect nucleation sites under radiation. This is investigated on gallium nitride high-electron-mobility transistors (GaN HEMTs). Using transmission electron microscopy, we spatially resolved the stress field in the AlGaN layer for both pristine and 10 Mrad gamma-irradiated HEMTs. The quantitative nanobeam electron diffraction and geometric phase analysis indicate that tensile stressed localizations experience higher radiation-induced strain. This finding is explained by the tensile stress dependence of the carrier concentration and mobility in the AlGaN layer. Since gamma radiation damage is inflicted by high-energy electrons only, localized regions of higher tensile stress in the AlGaN layer are expected to be more susceptible to gamma rays.