Piezoelectric strain in AlGaN∕GaN heterostructure field-effect transistors under bias

Micro-Raman spectroscopy was used to study piezoelectric strain in AlGaN∕GaN heterostructure field-effect transistors under bias. The measurements were made through the transparent SiC substrate. Strain in the GaN layer varied over the device area and was dependent on bias voltage, and affected, in particular, the gate-drain gap and area underneath the drain contact. The observed strain in GaN was shown to be related to the electric field component normal to the surface. Finite element simulations of electric field distribution show good qualitative agreement with the experimental data. Effects of strain on Raman temperature measurements in transistors are also discussed.