Improved RF Power Performance of AlGaN/GaN HEMT Using by Ti/Au/Al/Ni/Au Shallow Trench Etching Ohmic Contact

In this article, we report on the high dc and RF performance of AlGaN/GaN high electron mobility transistors that employ Ti/Au/Al/Ni/Au metallization stack with shallow trench etching ohmic contact (STEOC). An excellent ohmic contact performance including low contact resistance (
${R}_{C}$
) of
$0.28~\Omega \cdot $
mm and smooth surface morphology have been achieved simultaneously. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (rms) roughness of 6.3 nm even after 810 °C high-temperature annealing (HTA), achieving an improvement of 79% as compared to the conventional Ti/Al/Ni/Au ohmic contact (COC). A high-resolution transmission electron microscope (HRTEM) showed a glossy morphology with a continuous and uniform TiN layer formed in the interface for the STEOC sample, while a bumpy morphology caused from the Ni-Al complexes balling up and TiN island penetrating into the AlGaN/GaN heterostructure were observed for the conventional sample. Consequently, the fabricated transistors with the STEOC process show a high output current of 1.52 A/mm and low ON-resistance (
${R}_{ \mathrm{ ON}}$
) of
$2.09~\Omega $
mm. In addition, a high current cutoff frequency (
${f}_{T}$
) of 60 GHz and maximum oscillation frequency (
${f}_{\text {max}}$
) of 150 GHz were obtained for the STEOC HEMT with a gate length (
${L}_{\text {g}}$
) of 150 nm. Sub-6 GHz continuous-wave mode power sweep measurements deliver a high power-added-efficiency (PAE) of 67%. These results show the significant potential of the STEOC process to facilitate the development of GaN-based power amplifier (PA) applied for 5G.