Microwave performance of AlGaN/GaN inverted MODFET's

A continuous wave output power of 1.5 W/mm with a power added efficiency of 17.5% has been achieved at 4 GHz in inverted AlGaN/GaN MODFET's (IMODFET's) with 2 mu m gate lengths and 78 mu m gate widths, The current gain and available power gain cutoff frequencies were 6 and 11 GHz, respectively. We suggest that the input characteristics of GaN-based FET's play an important role in the output power that can be obtained, In the present devices, high transconductance, 100 mS/mm, retained over a 5 V input swing is thought to alleviate the limitations imposed by the input characteristics. Moreover, the buried AlGaN buffer layer is suggested as having assisted in the reduction of the output conductance which aides the power gain.