Xiaolei Chu¹, Yi Zhang¹, Valerie Brogden¹, Esaul Garza¹, Akansha Eling¹, Carlos Amaral¹, Cecile S. Bonifacio², Patrick Darmawi-Iskandar^3
1Covalent, Sunnyvale CA
²E.A. Fischione Instruments, Export, PA
³Massachusetts Institute of Technology, Boston, MA
High-electron-mobility transistor (HEMT) heterostructures rely on strain-driven polarization at the AlGaN/GaN interface to form and control the 2DEG channel, but unintended stress sources (e.g., wafer bow, packaging stress, thermal cycling, or process-induced stress) can modify strain and polarization fields, contributing to wafer-to-wafer or lot-to-lot drift in electrical performance. To investigate an out-of-spec GaN/AlGaN multilayer stack, we combined scanning precession electron diffraction (PED) with differential phase contrast (DPC) STEM to connect nanoscale structure to electrostatic behavior at relevant defect and interface length scales. PED was used to map spatial variations in local lattice parameters and strain gradients across the multilayers, revealing non-uniform strain both between layers and within individual layers that co-varied with microstructural features such as orientation changes and boundary density. DPC-STEM was then used to visualize corresponding spatial variations in beam deflection attributed to local electric-field differences, providing direct evidence of strain-associated polarization heterogeneity within the heterostructure. Together, the correlated PED strain/orientation maps and DPC field maps provide an experimentally grounded pathway to diagnose strain–polarization variability mechanisms in GaN HEMT stacks and to guide process and integration adjustments aimed at stabilizing target electrical performance.