Dispersion-free operation in InAlN-based HEMTs with ultrathin or no passivation

The origin and management of DC-RF dispersion in InAlN-based GaN high electron mobility transistors (HEMTs) is examined, in conjunction with consideration of the implications for device speed. This study, in which GaN HEMTs with alloyed and non-alloyed ohmic contacts are compared, renders the following observations and hypotheses: 1) We show and explain that dispersion free operation can be achieved without passivation. 2) The root cause of dispersion associated with surface states is often introduced during device processing; in particular, unintentional or un-optimized oxidation of the HEMT surface. 3) These undesired surface states also lead to gate extension (virtual gate), which decreases device speed but increases the breakdown voltage. In addition, the function and efficacy of a plasma-based ultrathin passivation is evaluated.