Input Noise Voltage Below 1 nV/Hz1/2 at 1 kHz in the HEMTs at 4.2 K

Specific High Electron Mobility Transistors (HEMTs) have been realized and characterized. At 4.2?K, with a drain-source current I _ds of 1.55?mA and drain-source voltage V _ds of 100?mV, the transistor has the following electrical characteristics: a?transconductance and an output conductance of 69 and 3.8?mS, respectively, leading to an intrinsic voltage gain of?18; an input gate-source capacitance C _gs of about 31?pF; and a gate leakage current less than 0.2?pA. An equivalent input noise voltage lower than 1?nV/Hz^1/2 at 1?kHz has been achieved when I _ds=1.55?mA at V _ds=100?mV. Hence, our results show that the specific HEMTs should be a suitable transistor for future ultra-low noise deep cryogenic low-frequency high-impedance readout electronics.