Sub-30-nm In_0.8Ga_0.2As Composite-Channel High-Electron-Mobility Transistors With Record High-Frequency Characteristics

We present sub-30-nm In _0.8 Ga _0.2 As composite-channel high-electron-mobility transistors (HEMTs) with outstanding dc and high-frequency characteristics. We adopted a composite-channel design with an In _0.8 Ga _0.2 As core layer, which led to superior carrier transport properties such as a Hall mobility ( μ _{n_Hall} ) of 13500 cm ² / V·s. The device with L _g = 19 nm exhibited an excellent combination of dc and RF properties, including R _ON = 271Ω-μm, g _{m_max} = 2.8 mS / μm, and f _T / f _max = 738 / 492 GHz. To understand the physical origin of such an excellent combination of dc and RF responses, we analyzed the effective mobility ( μ _{n_eff} ) and delay time for both long- and short- L _g devices, revealing a very high μ _{n_eff} value of 13200 cm ² / V·s and an average velocity under the gate ( v _avg ) of 6.2×10 ⁷ cm / s. We also studied the impact of the electrostatic integrity of the device, finding that the intrinsic output conductance (g _oi ) played a role in determining f _T and f _max in short- L _g HEMTs.