Epitaxial Optimization of 130-nm Gate-Length InGaAs/InAlAs/InP HEMTs for Low-Noise Applications

The epitaxial structure of 130- nm gate-length InGaAs/InAlAs/InP high electron mobility transistors (HEMTs) has been studied in order to optimize the device performance when biased under low-noise conditions. Three essential epitaxial parameters have been varied: the In channel content ([In]: 53%, 70%, and 80%), the delta-doping concentration (delta: 3, 5, and 7 times 10¹² cm^-2), and the Schottky layer thickness (d_SL: 9,11, and 13 nm). All HEMTs exhibited low gate-leakage current I_G below 1 muA/mm at a low-noise bias, except d_SL = 9 nm due to a too thin Schottky layer thickness. It was verified that the lowest noise figure NF was achieved when the square root of the drain-to-source current I_DS over transconductance g_m exhibited a minimum. A clear optimum for both d_Sl and delta was observed with respect to minimum noise figure NF_min. Increasing [In] only provided a slight reduction in N-F_min. In contrast, the RF performance was much more affected by increasing [In]. The lowest NF_min was achieved with a delta doping of 5 times 10¹² cm² and a d_SL of 11 nm.