AlGaN/GaN heterostructure field-effect transistor with semi-insulating Mg-doped GaN cap layer

We report the fabrication of AlGaN/GaN heterostructure field-effect transistor (HFET) with in situ grown semi-insulatingMg-doped GaN (GaN:Mg) cap layer. Without activation, the GaN:Mg film is known to be highly resistive and shown to reduce leakage current in AlGaN/GaN heterostructure. With 1-m-long gate length at drain-voltage of 10V, the presented HFET exhibited a drain-source current in saturation (IDSS) of 735 mA/mm and a peak transconductance gm(max) of 170 mS/mm, while the current gain cutoff frequency (f_T) and maximum frequency of oscillation (f_max) were 20.5 and 33.3 GHz, respectively.