InAlN/GaN HEMT With n⁺GaN Contact Ledge Structure for Millimeter-Wave Low Voltage Applications

In this work, high performance InAlN/GaN HEMT based on the n+GaN regrown ohmic contact with n+GaN contact ledge structure is proposed. The regrown ohmic contact of InAlN/GaN HEMT is formed by MBE n+GaN regrowth and self-stopping etching, which makes the total ohmic contact resistance between the 2DEG channel and the ohmic metal decrease to $0.12 \Omega \cdot $ mm and forms n+GaN contact ledge structure. Owing to the n+GaN contact ledge on the InAlN barrier, with the increasing of drain-source voltage (VDS), an additional current path comes into being between the n+GaN contact ledge on the InAlN barrier and the 2DEG channel, which can “shorten” the device effective drain-source distance, thus further reducing the parasitic resistance. Compared with regrown InAlN/GaN HEMT without n+GaN contact ledge structure, the peak transconductance (Gm.max) of regrown InAlN/GaN HEMT with n+GaN contact ledge structure increases from 747 mS/mm to 874 mS/mm, and the saturation current density (ID.max) increases from 2.6 A/mm to 2.9 A/mm. Besides, the self-stopping etching on the access region does not induce extra defects, and negligible current collapse is obtained. As the results of low parasitic resistance, high output current density, low knee voltage and negligible current collapse, power-added-efficiency (PAE) of 44% together with output power density (Pout) of 2.5 W/mm is achieved at 30 GHz and $V_{\mathrm{ DS}}$ of 10 V, which indicates regrown InAlN/GaN HEMT with n+GaN contact ledge structure has great potential for millimeter-wave low voltage applications. Additionally, the transfer and schottky gate characteristics show negligible degradation after OFF/ON-state electrical stress tests.