CHARACTERISTICS OF 0.8-MU-M AND 0.2-MU-M GATE LENGTH INXGA1-XAS IN0.52AL0.48AS INP (0.53-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.70) MODULATION-DOPED FIELD-EFFECT TRANSISTORS AT CRYOGENIC TEMPERATURES

We have investigated analytically and experiment tally the performance characteristics of InP-based InxGa1-xAs/In0.52Al0.48As (0.53 less-than-or-equal-to x less-than-or-equal-to 0.70) pseudomorphic modulation-doped field-effect transistors (MODFET's) as a function of strain in the channel, gate, length, and temperature. The strain in the channel was varied by varying the In composition x. The temperature was varied in the range of 40-300 K and the devices have gate lengths L(g) of 0.8 and 0.2-mu-m. Analysis of the device was done using a one-dimensional self-consistent solution of the Poisson and Schrodinger equations in the channel, a two-dimensional Poisson solver to obtain the channel electric field, and a Monte Carlo simulation to estimate the carrier transit times in the channel. An increase in the value of the cutoff frequency is predicted for an increase in In composition, a decrease in temperature, and a decrease in gate length. The improvements seen with decreasing temperature, decreasing gate length, and increased In composition were smaller than those predicted by analysis. The experimental results on pseudomorphic InGaAs/InAlAs MODFET's have shown that there is a 15-30% improvement in cutoff frequency in both the 0.8- and 0.2-mu-m gate length devices when the temperature is lowered from 300 to 40 K.