Polarization-controlled modulation doping of a ferroelectric from first principles

TL;DR

This paper uses first-principles calculations to explore how ferroelectric materials in FeFETs can actively contribute to device conductance through modulation doping, guiding materials selection for improved device performance.

Contribution

It provides a detailed first-principles analysis of modulation doping in ferroelectric heterostructures, expanding understanding of active FeFET mechanisms and offering a predictive electrostatic model.

Findings

Modulation doping is significant in BaTiO3/n-SrTiO3 and PbTiO3/n-SrTiO3 heterostructures.

An electrostatic model accurately describes charge transfer distribution.

Guidelines for materials and interface design in active FeFETs are proposed.

Abstract

In a ferroelectric field effect transistor (FeFET), it is generally assumed that the ferroelectric gate plays a purely electrostatic role. Recently it has been shown that in some cases, which could be called 'active FeFETs', electronic states in the ferroelectric contribute to the device conductance as the result of a modulation doping effect in which carriers are transferred from the channel into the ferroelectric layers near the interface. Here we report first-principles calculations and model analysis to elucidate the various aspects of this mechanism and to provide guidance in materials choices and interface termination for optimizing the on-off ratio, using BaTiO3/n-SrTiO3 and PbTiO3/n-SrTiO3 as prototypical systems. It is shown that the modulation doping is substantial in both cases, and that extension of an electrostatic model developed in previous work provides a good description of the transferred charge distribution. This model can be used to suggest additional materials heterostructures for the design of active FeFETs.