A study of electron transit-time in ballistic diodes using a multi-valley hydrodynamic transport model

The use of a multivalley hydrodynamic transport model to investigate electron transit time through submicron GaAs electron device structures is discussed. The study was performed to determine the feasibility of utilizing the velocity overshoot effect in reducing the overall transit time. This model, which incorporates a separate set of hydrodynamic equations for each conduction band valley (Γ, L and X) and allows for electron exchange through energy dependent relaxation parameters, is applied to a structure which reduces upper valley occupancy and enhances device transit time. The results of this study indicate that, while velocity speed-up in minimal in the neighborhood of the active (low-doped) region, the velocity overshoot can be extended into the collector region (high-doped region) with significant transit time enhancement