Subsurface Fe-doped semi-insulating GaN templates for inhibition of regrowth interface pollution in AlGaN/GaN HEMT structures

The regrowth of AlGaN/GaN high electron mobility transistor (HEMT) structures on semi-insulating (SI) GaN templates, after exposure to air, results in the presence of parasitic conducting channels at regrowth interface (RI). Air contamination of the SI GaN templates is responsible for n-type doping and explains this parallel conduction. The parasitic conducting channel results in poor pinch-off characteristics (Ileakage∼1 mA/mm at bias gate–source voltage above pinch-off voltage) and poor inter-device isolation and makes necessary to equip reactors with acceptor sources to compensate the n-type doping at the RI. To overcome this, we developed a new method of local Fe doping used in GaN templates for inhibiting RI pollution and proved to be efficient. Using this annihilation method permits to reduce by several orders of magnitude buffer leakage current. Such HEMT structures regrown by metalorganic vapor phase epitaxy (MOVPE) or by molecular beam epitaxy (MBE) exhibit two-dimensional electron gas (2DEG) with 300 K mobilities above 2000 cm2/V s at carrier densities 9–10×1012 cm−2 with a perfect charge control.