An analytical noise evaluation for super low-noise InAlAs/InGaAs/InAlAs/InP HEMTs

An analytical model for super low-noise InAlAs/InGaAs/InAlAs/InP HEMTs is presented. The carriers are well confined in the quantum well formed in InGaAs due to the large conduction band discontinuities (ΔEC) at the InAlAs/InGaAs and InGaAs/InAlAs heterointerfaces. Moreover, a smaller electron effective mass in InGaAs results in a higher device transconductance g_m and lower noise figure NF. The noise figure of InP based HEMTs is much lower than that of GaAs based pseudomorphic or normal HEMTs. The present model is based on a self-consistent solution of Schroedinger and Poisson´s equations to calculate the properties of the quantum well formed in InGaAs, namely the average distance of two-dimensional electron gas (2DEG), x_av , and the position of Fermi level, E_F, as a function of 2DEG concentration n_s. Instead of using a two-line or an exponential approximation, an improved velocity electric field (v_d -E) characteristic is used to calculate the current-voltage (I-V) characteristics, small-signal parameters and noise performance analytically. Based on the model developed by Liu and Anwar et al., g _m is calculated and the result shows an excellent agreement with experimental data. The present model yields a minimum noise figure, F_min, of 0.8 and 1.2 dB at 60 and 94 GHz, respectively, which well fit to the experimental data. The noise performance of this class of devices with different gate lengths is studied in the present model