<i>In situ</i> nanobeam x-ray diffraction of local strain in AlGaN/GaN high-electron-mobility transistors under operating condition

We combined the synchrotron radiation nanobeam x-ray diffraction technique with the pump–probe method to perform in situ measurements of local strain in a normally ON AlGaN/GaN metal–oxide–semiconductor high electron mobility transistor device under transistor operation. The c-axis strain in the AlGaN barrier layer within the gate region exhibited a clear position dependence, increasing as the gate voltage was increased in the negative direction and as the measurement position moved from the center of the gate electrode toward the drain-side gate edge. Based on the characteristics of the measured c-axis and a-axis strains, we successfully extracted not only the strain component due to the inverse piezoelectric effect but also the thermal expansion strain component, using the constitutive equation for elastic bodies. From the characteristics of the device current measured simultaneously with the strain measurements, it was revealed that the temperature rise inducing the thermal expansion strain was caused by the transient and steady-state drain currents.