Impact of X-Ray Radiation on GaN/AlN MEMS Structure and GaN HEMT Gauge Factor Response

We present electrical measurements of gallium nitride/Aluminum nitride (GaN/AlN) microelectromechanical system (MEMS) beams under the combined influence of strain and X-ray radiation. These results are used to understand the mechanism for the observed piezoresistive gauge factor in GaN devices. Exposure with X-ray radiation decreases the electrical resistance while strongly suppressing the gauge factor. Upon removal of the X-ray, the gauge factor quickly returns to its pre-radiated value, while the electrical resistance remains low for a long period of time. These results suggest that the piezoresistance is mainly due to the generation of piezoelectric fields, which are screened by the mobile charge excited by the X-ray radiation. Preliminary results are also presented for HEMT devices; here, piezoelectric fields shifts the threshold voltage of the transistor resulting in an increase in drain current.