Modeling of short-pulse threshold voltage shifts due to DX centers in Al/sub x/Ga/sub 1-x/As/GaAs and Al/sub x/Ga/sub 1-x/As/In/sub y/Ga/sub 1-y/As MODFET's

The DX-center-related short-pulse threshold voltage shifts (SPTVS) in Al/sub x/Ga/sub 1-x/As-based MODFETs is modeled using CBAND, a simulator that solves Poisson equations self-consistently with Schrodinger equations and donor statistics. Using values given in the literature for the DX energy level in Al/sub x/Ga/sub 1-x/As this technique gives good agreement between measured and simulated SPTVS for Al/sub 0.3/Ga/sub 0.7/As/GaAs and Al/sub 0.3/Ga/sub 0.7/As/In/sub 0.2/Ga/sub 0.8/As MODFETs. Both simulation and experiment show that the use of Al/sub 0.2/Ga/sub 0.8/As in the donor layer reduces the SPTVS relative to the structures using Al/sub 0.3/Ga/sub 0.7/As. However, the measured shifts at this composition are considerably lower than the simulated values, indicating a DX energy level that may be higher than the value extrapolated from the literature, possibly due to the existence of multiple trap levels. Despite this discrepancy, these results support the use of strained-channel layers and lower Al/sub x/Ga/sub 1-x/As compositions in MODFETs for digital and other large-signal applications requiring good threshold stability.<
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