High-Performance Low-Leakage-Current AlN/GaN HEMTs Grown on Silicon Substrate

In this letter, ultrathin-barrier AlN/GaN high-electron mobility transistors (HEMTs) capped with in situ metal-organic-chemical-vapor-deposition-grown SiN have been successfully fabricated on 100-mm Si substrates. Output current density exceeding 2 A/mm has been reached, which represents, to the best of our knowledge, the highest value ever achieved for GaN-on-Si HEMTs. This results from the high 2DEG density of the optimized AlN/GaN heterostructure. Despite the ultrathin barrier of 6 nm, low gate and drain leakage currents of about 10 μA/mm are obtained without the use of a gate dielectric that generally induces reliability issues. Furthermore, the high aspect ratio (gate length L_g/gate-to-channel distance) and low RF losses (at the buffer/Si substrate interface) are reflected in excellent RF performances. The current gain extrinsic cutoff frequency f_T and the maximum oscillation frequency f_max were 52 and 102 GHz with a 0.2- μm gate length, respectively, resulting in an f_T·L_g product as high as the reported state-of-the-art GaN-on-Si HEMTs.