Fig. 3. Electrical performance of cryogenic III-V HEMT on Si for low noise amplifier.

Transfer (a) and transconductance (b) characteristics of III–V HEMTs on Si with L_G of 70 nm and W_G of 2 × 20 μm measured at V_DS of 50 (dashed) and 100 mV (solid). The measurements were conducted at 300 K and 4 K. When cooled to 4 K, the device exhibits transfer characteristics with improved SS of 35 mV dec⁻¹ at V_DS = 50 mV. The positive threshold voltage (V_TH) shift is also observed. The device offers sharper g_m characteristics and a high peak g_m of 0.8 S mm⁻¹ at 4 K for a low V_DS of 100 mV, compared to those observed at 300 K. This improvement at 4 K is attributed to enhanced 2DEG mobility and a reduction in parasitic resistance. c Output characteristics of the same device, showing improved on-resistance and increased maximum current at 4 K. d Noise indication factor versus I_D of the device at a low V_DS of 50 and 100 mV. The measurements were conducted at 300 K and 4 K. The device shows a very low noise indication factor of 0.21 $0.21\sqrt{\mathrm{Vmm}}\sqrt{S^{-1}}$ and the P_DC at minimum noise indication factor is only 0.8 and 2 mW mm⁻¹ at V_DS = 50 and 100 mV. Gain plots of III–V HEMTs on Si with L_G of 70 nm and W_G of 2 × 20 μm measured at 300 K (e) and 4 K (f). The measurements were conducted at V_DS of 500 mV and the optimal V_GS for each temperature. The f_T and f_MAX are extracted by extrapolating the h₂₁ and U curves with −20 dB dec⁻¹ lines.