Sub-30-nm In0.8Ga0.2As 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.