Characterization of InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic In
y
Ga
1-y
As/Al
0.15
- Ga
0.85
As (
0.05 \le y \le 0.2
) MODFET's grown by MBE have been characterized at dc (300 and 77 K) and RF frequencies. Transconductances as high as 310 and 380 mS/mm and drain currents as high as 290 and 310 mA/mm were obtained at 300 and 77 K, respectively, for 1-µm gate lengths and 3-µm source-drain spacing devices. Lack of persistent trapping effects,
I-V
collapse, and threshold voltage shifts observed with these devices are attributed to the use of low mole fraction Al
x
Ga
1-x
As while still maintaining 2DEG concentrations of about 1.3 × 10
¹²
cm
^-2
. Detailed microwave S-parameter measurements indicate a current gain cut-off frequency Of 24.5 GHz When
y = 0.20
, which is as much as 100 percent better than similar GaAs/AlGaAs MODFET structures, and a maximum frequency of oscillation of 40 GHz. These superior results are in part due to the higher electron velocity of InGaAs as compared with GaAs. Velocity field measurement performed up to 3 kV/cm using the magnetoresistance method indicates an electron saturation velocity of greater than 1.7 × 10
⁷
cm/s at 77 K for
y = 0.15
, which is 20 percent higher than GaAs/AlGaAs MODFET's of similar structure.