Subthreshold Mobility in AlGaN/GaN HEMTs

Electron mobility of AlGaN/GaN HEMTs is studied using a gate admittance-based technique. This analysis extends to electron densities as low as 4×10
¹⁰
cm
^-2
with good accuracy. Zero lateral electric field is applied, in contrast to conventional methods. At these low electron densities, the mobility can be a factor of ~50 less than that in the ON-state. We reveal a regime at low electron densities where the screening of the two dimensional electron gas (2-DEG) becomes negligible causing the mobility to be independent of electron concentration, suggesting percolative transport. This region defines the rate at which the channel depletes and is a strong indicator of the epitaxial control of the impurities in the GaN channel.