Abstract
An In0.53(AlxGa1–x)0.47As quaternary channel has been introduced into n+-InAlAs/InGaAs HEMTs. By adding a small amount of Al to the InGaAs channel, the bandgap can be enhanced, which provides a higher reversed gate-drain breakdown voltage. In addition, the associated impact ionisation process can be suppressed in these quaternary channels. These HEMTs have been demonstrated with a very low output conductance (4 mS/mm for x = 0.2) and a much smaller gate leakage current than conventional InP-HEMTs.