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)