MODFET 2-D hydrodynamic energy modeling: optimization of subquarter-micron-gate structures

Harmonic solution of semiconductor transport equations for microwave and millimetre-wave device modelling

“…These terms have little impact in our case, as their effect is felt especially when strong discontinuities are present in the direction of the charge flow. Poisson's and continuity equations are solved simultaneously because of their strong coupling; the other two conservation equations are solved iteratively by recomputing the values of the relaxation time constants at each iteration, until the solution converges to a stable value [12]. The efficiency of the proposed approach becomes apparent from the comparison of the computational times, which are thus usually reduced by one to more than two orders of magnitude with respect to the traditional time-domain approach, as reported in the following.…”

Investigation into intermodulation distortion in HEMTs using a quasi-2-D physical model

“…The reasons for the fall in around pinchoff are the depletion of the 2 DEG layer of electrons and deconfinement of electrons from the quantum-well channel: electrons are injected from the channel into the buffer and contribute to channel current, but with a lower mobility than in the 2 DEG channel. These electrons are far from the gate so charge control, and hence transconductance, is reduced [12]. This can be interpreted as a shift in the effective position of the 2 DEG layer, which is dependent on the gate voltage, with a consequent nonlinear relationship between channel carrier concentration and gate voltage [13] (5) where is the 2 DEG sheet charge density, is the distance from the gate to the heterointerface, is the effective position of the 2 DEG (which is dependent on gate bias), is the gate voltage, and the threshold voltage.…”

“…This can be interpreted as a shift in the effective position of the 2 DEG layer, which is dependent on the gate voltage, with a consequent nonlinear relationship between channel carrier concentration and gate voltage [13] (5) where is the 2 DEG sheet charge density, is the distance from the gate to the heterointerface, is the effective position of the 2 DEG (which is dependent on gate bias), is the gate voltage, and the threshold voltage. The transconductance falls around forward-bias gate voltages due to the onset of parallel conduction in the doped donor layer (AlGaAs in a conventional GaAs/AlGaAs HEMT) and saturation of the 2 DEG layer [12]. The build-up of charge in the (low mobility) donor layer shields the 2 DEG layer from the charge-control effects of the gate, thus reducing transconductance.…”

MESFET models for microwave CAD applications

“…The models have not yet been developed to the point where they can be efficiently used to simulate the R F performance of a device. In general, nonequilibrium phenomena can be simulated using hydrodynamic [27], numerical [25], or Monte Carlo [28] solution techniques. These models are very useful for investigating in detail the physical operation of the device.…”