Low-Field Mobility and High-Field Velocity of Charge Carriers in InGaAs/InP High-Electron-Mobility Transistors

Development of transistors for advanced low-noise amplifiers requires better understanding of mechanisms governing the charge carrier transport in correlation with the noise performance. In this article, we report on study of the carrier velocity in InGaAs/InP high-electron mobility transistors (HEMTs) found via geometrical magnetoresistance in the wide range of the drain fields, up to 2 kV/cm, at a cryogenic temperature of 2 K. We observed, for the first time experimentally, the velocity peaks and found that the peak velocity and corresponding field decrease significantly with the transverse field. The low-field mobility and peak velocity are found to be up to 65 000 cm(2)/Vs and 1.2 x 10(6) cm/s, respectively. Extrapolations to the lower transverse fields show that the peak velocity can be as high as 2.7 x 10(7) cm/s. The corresponding intrinsic transit frequency can be up to 172 GHz at the gate length of 250 nm. We demonstrated, for the first time, that the low-field mobility and peak velocity reveal opposite dependencies on the transverse field, indicating the difference in carrier transport mechanisms dominating at low and high fields. Therefore, the peak velocity is an appropriate parameter for characterization and development of the low-noise HEMTs, complementary to the low-field mobility. Analysis indicates that the low-field carrier transport is governed by screening of the Coulomb potential of ionized impurities responsible for the carrier scattering. The velocity overshoot is associated with the electron quantization and subband formation caused by the transverse field. The results of the research clarify the ways of the further development of the HEMTs for advanced applications.