Velocity Enhancement in Cryogenically Cooled InP-Based HEMTs on (411)A-Oriented Substrates

An extremely high maximum transconductance g mmax of 2.25 S/mm and a cutoff frequency f T of 310 GHz was achieved at a cryogenic temperature (16 K) in a 195-nm-gate In 0.75 Ga 0.25 As/In 0.52 Al 0.48 As high electron mobility transistor (HEMT) fabricated on a (411)A-oriented InP substrate by molecular beam epitaxy, compared with room temperature values (g mmax =1.78 S/mm and f T =245 GHz). These significantly enhanced g mmax and f T values are attributed to a high electron velocity of up to 4.9times10 7 cm/s due to suppressing phonon scattering in the In 0.75 Ga 0.25 As/In 0.52 Al 0.48 As HEMT with (411) A super-flat InGaAs/InAlAs interfaces (effectively atomically flat heterointerfaces over a wafer-size area)