An investigation of i-AlGaAs/n-GaAs doped-channel MIS-like FET's (DMT's)—Properties and performance potentialities

Doped-channel MIS-like FET's (DMT's) based upon an i-AlGaAs/n-GaAs structure have been investigated in detail for the purpose of clarifying their properties and performance potentialities. The DMT is unique in having two operation modes, a depletion-layer modulation mode and an electron accumulation mode, both of which are experimentally demonstrated through capacitance-voltage characteristics. Analytical and experimental results shows that the maximum drain current I
DSmax
is more than 2.5 times that for a conventional n-AlGaAs/GaAs 2DEGFET. g
mmax
and I
Dsmax
values obtained for 0.5- µm gate DMT's are very high, 310 mS/mm (410 mS/mm) and 650 mA/mm (800 mA,/mm) at 300 K (77 K), respectively, f
max
is 48 GHz. f
T
is as large as 45 GHz, which is the best data ever reported in 0.5-µm gate FET's. Moreover, the estimated electron saturation velocity is outstandingly large, 1.5 × 10
⁷
cm/s (2 × 10
⁷
cm/s) at 300 K (77 K), even for a thin GaAs channel layer with a 3 × 10
¹⁸
cm
^-3
doping level, while Hall electron mobility is not reasonably so high, being typically 1850 cm
²
/V . s (1650 cm
²
/V . S). Preliminary power performances are also studied at 28.5 GHz. An 18-dBm (225-mW/mm) saturation output power, 6.4-dB linear gain, and 15-percent power added efficiency are achieved. A further performance improvement may be easily accomplished by gate length reduction, structure optimization, and so on. Consequently, it has been proved that DMT's have great feasibility for high-speed and high-frequency high-power device applications.