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 ( $\boldsymbol \mu _{n{\boldsymbol \_{}}\text {Hall}}$ ) of 13500 cm $^{{2}} \boldsymbol /\text{V}\cdot \text{s}$ . The device with ${L}_{g} \boldsymbol {=}\,\,19$ nm exhibited an excellent combination of dc and RF properties, including ${R}_{ \mathrm{\scriptscriptstyle ON}} \boldsymbol {=}\,\,271\Omega $ - $\boldsymbol \mu \text{m}$ , ${g}_{m{\boldsymbol \_{}}\text {max}} \boldsymbol {=}\,\,2.8$ mS ${\boldsymbol /} \boldsymbol \mu \text{m}$ , and ${f}_{\text {T}} \boldsymbol / {f}_{\text {max}} \boldsymbol {=}\,\,738\boldsymbol /492$ GHz. To understand the physical origin of such an excellent combination of dc and RF responses, we analyzed the effective mobility ( $\boldsymbol \mu _{n{\boldsymbol \_{}}\text {eff}}$ ) and delay time for both long- and short- ${L}_{g}$ devices, revealing a very high $\boldsymbol \mu _{n{\boldsymbol \_{}}\text {eff}}$ value of 13200 cm $^{{2}} \boldsymbol /\text{V}\cdot \text{s}$ and an average velocity under the gate ( ${v}_{\text {avg}}$ ) of $6.2\times 10^{{7}}$ cm $\boldsymbol /\text{s}$ . We also studied the impact of the electrostatic integrity of the device, finding that the intrinsic output conductance ( ${g}_{\text {oi}}$ ) played a role in determining ${f}_{\text {T}}$ and ${f}_{\text {max}}$ in short- ${L}_{g}$ HEMTs.