High voltage InAlN/GaN HEMTs with nonalloyed Source/Drain for RF power applications

In this work, we propose the nonalloyed Schottky Source/Drain (SSD) technology for high voltage InAlN/GaN HEMTs. The proposed device features excellent metal morphology both in lateral and vertical benefiting from the removal of metallic overflow associated with the conventional alloyed Ohmic contacts, which bodes well for device scaling and high breakdown voltage (BV) obtained in the proposed device. The nonalloyed Source/Drain (S/D) also paves the way for the SSD HEMTs using a gate-first fabrication process with the standard Ni/Au gate stack. Despite the Schottky Source/Drain, an SSD HEMT with L_G = 1.25 μm exhibits a decent maximum drain current of 575 mA/mm and peak transconductance of 216 mS/mm. The corresponding BV is 58 V which is the highest BV reported on GaN HEMTs for a short L_GD of 250 nm. Without using any field-plate structure, the BV of 605 V is achieved in an SSD HEMT with L_GD = 15 μm, realizing 229% improvement compared with the conventional InAlN/GaN HEMTs. The proposed SSD technology featuring scaling capability and high breakdown voltage is suitable for RF power applications and can be further developed for self-aligned InAlN/GaN HEMTs.