Negative capacitance field-effect transistor (NCFET) and ferroelectric field-effect transistor (FE-FET) devices and methods of forming are provided. The gate dielectric stack of the NCFET and FE-FET devices includes a non-ferroelectric interfacial layer formed over the semiconductor channel, and a ferroelectric gate dielectric layer formed over the interfacial layer. The ferroelectric gate dielectric layer is formed by inserting dopant-source layers in between amorphous high-k dielectric layers and then converting the alternating sequence of dielectric layers to a ferroelectric gate dielectric layer by a post-deposition anneal (PDA). The ferroelectric gate dielectric layer has adjustable ferroelectric properties that may be varied by altering the precisely-controlled locations of the dopant-source layers using ALD/PEALD techniques. Accordingly, the methods described herein enable fabrication of stable NCFET and FE-FET FinFET devices that exhibit steep subthreshold slopes.