Impact of AlN interalayer on reliability of AlGaN/GaN HEMTs

RF stability measurements have been performed on over 300 MBE and MOCVD grown devices with and without a thin (similar to 10 angstrom) AIN interlayer located between the AlGaN barrier and GaN channel. 70% of devices with the AIN interlayer showed an increase in gate leakage during RF stress, while only 28% of the devices without the AIN interlayer showed an increase in gate leakage during RF stress. An increase in gate leakage is inconsistent with increased trapping as the degradation mechanism for decreased output power. The unusual increase of gate leakage in devices with AIN interlayers was further explored. The results suggest one mechanism for the increase of gate leakage seen during RF stability measurements in devices with an AIN interlayer is due to localized breakdown along the gate finger caused by the inability to control the AIN interlayer thickness to within a monolayer along the entire gate width. Devices without an AIN interlayer typically exhibit a decrease in gate leakage with stress time, consistent with increased trapping at the gate edge.