The band alignment in AlGaN/GaN HEMT devices was investigated using scanning photocurrent microscopy (SPCM) with UV and visible light sources. The polarity of the SPCM on the conduction channel exhibited a switching behavior from p-type to n-type response as the gate bias was increased. The flat-band voltage, which was higher than the DC turn-on voltage, indicates that an ohmic metallic contact was formed for electron transport. We obtained the band offset between the conduction band and the metal Fermi level, which yielded a value of 2.1 eV on average.
This work was supported by the Midcareer Researcher Program ( 2017R1A2B4009177 ) through a National Research Foundation grant funded by Korea Government ( MSIP ) and by Human Resources Program in Energy Technology ( 20164030201380 ) of the Korea Institute of Energy Technology Evaluation and Planning ( KETEP ) grant funded by Korea Government ( MOTIE ). The research at Korea Advanced Nano Fab Center was supported by Nano∙Material Technology Development Program through the National Research Foundation of Korea funded by Ministry of Science, ICT and Future Planning ( 2015M3A7B7044548 ).
