Top-down drift-diffusion versus bottom-up quasi-ballistic formalism in device compact modeling

In this paper, we start with a review of the basics in the drift-diffusion (DD) and quasi-ballistic (QB) formalisms in the context of field-effect transistor (FET) compact modeling (CM). In general, analytic CMs are derived with simplifying approximations, and they are validated with the corresponding theories by numerical simulations; e.g., by numerically solving the Shockley DD equations or coupled Schrödinger-Poisson equations. However, in validating either approach, comparisons with experimental devices would be important. For this purpose, we make a critical comparison of the two CMs based on the DD and QB formalisms with the state-of-the-art nanoscale GaN high electron-mobility transistors (HEMTs). The role of velocity saturation is explored and compared in both the DD and QB formulations. Finally, we discuss on the model scalability and applicability for both approaches in real-life devices.