Evaluation of titanium disilicide/copper Schottky gate for AlGaN/GaN high electron mobility transistors

Titanium disilicide/copper (TiSi₂/Cu) gate AlGaN/GaN high electron mobility transistors (HEMTs) with low gate leakage current are demonstrated. The TiSi₂/Cu gate devices demonstrate electrical characteristics that are comparable to those of conventional Ni/Au gate devices. At gate voltage of -20 V, typical gate leakage current for a TiSi₂/Cu gate device with a gate length of 5 μm and width of 200 μm is found to be as low as 5.15 10^-7 mA mm^-1, which is three orders lower than that of the Ni/Au gate device. The lower gate leakage current is primarily caused by the higher Schottky barrier height of TiSi₂/Cu on AlGaN/GaN HEMTs than that of Ni/Au by 0.36 eV. The threshold voltages of the TiSi₂/Cu gate HEMTs were maintained to be equivalent to that of the Ni/Au gate device. No Cu diffusion was found at the metal and AlGaN interface by secondary ion mass spectrometry and scanning transmission electron microscopy. These results indicate that TiSi₂ is a good barrier layer of Cu diffusion, and titanium disilicide/copper is a promising candidate for high-performance AlGaN/GaN HEMTs.