L g = 19 nm In 0.8 Ga 0.2 As composite-channel HEMTs with f T = 738 GHz and f max = 492 GHz

We present L g = 19 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 that led to superior carrier transport properties. The device with L g = 19 nm displayed an excellent combination of R ON = 271 Ω-μm, g m_max = 2.5 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 13,200 cm2/V•s and an average velocity under the gate (v avg ) of 6.2 × 107 cm/s. We also studied the impact of the gate-to-source spacing (L GS ) and the electrostatic integrity of the device, finding that a reduction of L GS less than 0.6 μm was of little use in improving g m_max and f T . Additionally, the intrinsic output conductance (g o_int ) had an important impact on f T in short-L g HEMTs.