El. Piner et al., AlGaN/GaN high electron mobility transistor structure design and effects on electrical properties, MRS I J N S, 5, 2000, pp. NIL_299-NIL_303
We report on the effect of strain induced polarization fields in AlGaN/GaN
heterostructures due to the incorporation of Si dopant ions in the lattice.
By Si-doping (Al)GaN, a contraction of the wurtzite unit cell can occur le
ading to strain in doped AlGaN/GaN heterostructures such as high electron m
obility transistors (HEMTs). In a typical modulation doped AlGaN/GaN HEMT s
tructure, the Si-doped AlGaN supply layer is separated from the two-dimensi
onal electron gas channel by an undoped AlGaN spacer layer. This dopant-ind
uced strain, which is tensile, can create an additional source of charge at
the AlGaN:Si/AlGaN interface. The magnitude of this strain increases as th
e Si doping concentration increases and the AlN mole fraction in the AlGaN
decreases. Consideration of this strain should be given in AlGaN/GaN HEMT s
tructure design.