Sub-30-nm In0.8Ga0.2As Composite-Channel High-Electron-Mobility Transistors With Record High-Frequency Characteristics

We present sub-30-nm In0.8Ga0.2As composite-channel high-electron-mobility transistors (HEMTs) with outstanding dc and high-frequency characteristics. We adopted a composite-channel design with an In0.8Ga0.2As core layer, which led to superior carrier transport properties such as a Hall mobility (mu(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 = 271-mu m , g(m_max) = 2.8 mS/mu m , 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 (mu(n_eff)) and delay time for both long- and short-L-g devices, revealing a very high mu(n_eff) value of 13200 cm(2)/V.s and an average velocity under the gate (v(avg)) of 6.2 x 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.