Nonalloyed ohmic contacts in AlGaN/GaN HEMTs with MOCVD regrowth of InGaN for Ka-band applications

Abstract

Low-resistance ohmic contacts in AlGaN/GaN high-electron-mobility transistor (HEMT) devices require high-temperature (HT) annealing (>800 °C) which can deteriorate material quality, surface morphology, and edge acuity of the metal stacks. This article demonstrates the highfrequency and high-power performance of the AlGaN/GaN HEMT devices with low-temperature metal-organic chemical vapor deposition (MOCVD) regrown degenerately doped InGaN ohmic contacts compared with GaN-based regrown contacts. Ohmic contacts fabricated by regrowth methods could be a valuable alternative for both metal-based alloyed ohmic contacts and implantation-based ohmic contacts. Using a T-gate and MOCVD regrown InGaN ohmic contacts, the AlGaN/GaN HEMT with an Lg of 150 nm and S-D spacing of 2.5 μm demonstrated a maximum drain current of 0.94 A/mm and a peak transconductance of 337 mS/mm. The same device exhibited a forward current gain frequency ft of 36.8 GHz and a maximum frequency of oscillation fmax of 75.0 GHz. A power density of 3.07 W/mm with a 60% drain efficiency was measured at 35 GHz with a Vds of 20 V and a quiescent current of 100 mA/mm.