Photoluminescence characterization of the quantum well structure and influence of optical illumination on the electrical performance of AlGaN/GaN modulation-doped field-effect transistors

Electrical characteristics of high performance GaN modulation-doped field-effect transistors (MODFETs) grown by reactive molecular beam epitaxy method are studied experimentally both in dark and under white light illumination. The maximum measured drain-source current is 626 mA/mm in dark and 695 mA/mm under illumination, which saturates at a relatively low drain-source voltage VDS. The transconductance increases with decreasing gate length reaching a value of 210 mS/mm in dark and 222 mS/mm under illumination for devices with a gate length of LG=1.5μm. Breakdown voltages of about 90 V have also been exhibited by devices with gate length LG=1.5 μm and drain-gate distance LDG=1 μm. To our knowledge, these are the best values obtained so far from GaN MODFETs which we attribute to the suppression of leakage currents and improved materials structure of the devices.