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The correlation of the capacitance-voltage characteristics of fat MODFETs (FATFETs) to the current-voltage characteristics of FATFETs and the pulse-doped MODFET is reported. The measured gate capacitance is fitted using a noniterative numerical algorithm. The effective doping concentration of the GaAs buffer region and AlGaAs pulse-doped region is extracted along with the dependence of two-dimensional electron gas concentration upon the applied gate voltage. An excellent agreement between the threshold voltages calculated from the measured gate capacitance relation and the I-V characteristics is obtained for FATFETs. The correlation of the average threshold voltages of MODFETs and FATFETs appears to be technology-dependent. A good correlation of the average threshold voltage of MODFETs and FATFETs is observed on a wafer featuring Schottky gate diodes with good ideality coefficients. The comparison of the present semianalytic I-V model with a hydrodynamic model demonstrates that velocity overshoot above the GaAs peak stationary velocity does not appreciably improve the saturation transconductance. The two-dimensional field effects associated with the 2DEG channel width are also shown to bring a minimal contribution to the drain conductance of MODFETs.
Date of Publication: Nov 1989