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 10
¹²
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 10
¹²
cm
²
and a d
_SL
of 11 nm.