HEMT with nonalloyed ohmic contacts using n+-InGaAs cap layer

We have investigated nonalloyed ohmic contacts on HEMT´s using a highly conductive n⁺-InGaAs layer. The minimum specific contact resistance obtained was 4.8 × 10^-7Ω.cm², and the IV characteristics were equal to or better than those of conventional HEMT´s with alloyed ohmic contacts. The maximum transconductances of a nonalloyed ohmic HEMT were 240 mS/mm at 300K and 340 mS/mm at 88K for a gate length of 1.1 µm. We conclude that it is not necessary for HEMT´s with two-dimensional electron gas (2DEG) channels to have alloyed ohmic contacts, because the tunneling conduction is significant at the n-GaAs/n-AlGaAs/undoped GaAs double heterojunction.