Fabrication of high performance AlGaN/GaN FinFET by utilizing anisotropic wet etching in TMAH solution

AlGaN/GaN-based fin-shaped field-effect transistors (FinFETs) with very steep sidewall and various fin-widths (W_fin) have been fabricated by utilizing electron-beam lithography and additional anisotropic sidewall wet etch in tetramethyl ammonium hydroxide (TMAH) solution. The device with W_fin of 180 nm exhibits normally-on performance with threshold voltage of -3.5 V and extremely broad transconductance (g_m) characteristic ranging from -2 to ~ 3 V at V_D = 5 V which is essential for high linearity device performance. This broad g_m characteristic is because the current from the side-wall MOS channel becomes comparable to that from the two-dimensional electron gas (2DEG) channel and hence significantly contributes to the total device current. On the other hand, devices with smaller W_fin = 50 and 100 nm exhibit normally-off performance with positive threshold voltage of 2.0 and 0.6 V, respectively, and less broad g_m characteristics because the current from the side-wall MOS channel dominates the total device current.