Developing Phase Field Models for The Physical Vapor Deposition of Ferroic Doped AlN

While unique functionalities, such as ferroelectricity and ferromagnetism, have been observed in transition metal doped AlN thin films, the addition of these dopants can negatively impact the films crystalline quality. Avoiding phase segregation, surface faceting, or crystallite missorientation are critical to ensure that the full ferroic potential of these materials can be reached. Further insight into the microstructural evolution of AlN in the presence of transition metal dopants is necessary to understand the impact of these dopants on film growth and ferroelectricity.<br/>In this work, phase field models are developed for physical vapor deposition, microstructural development, and ferroelectric response of transition metal doped AlN thin films. These models are then compared to doped AlN thin films grown by pulsed laser deposition (PLD) and sputtering. Doped AlN thin films were deposited onto platinized silicon substrates via ultra-high-vacuum PLD, RF or DC sputtering. The substrate growth temperatures ranged from 200 °C to 800 °C with an incident laser energy from 100 to 300 mJ and a laser repetition rate of 10 Hz for PLD growth. Increasing the growth temperature decreases the full width, half maximum of the predominant (002) X-ray diffraction peaks, indicating an increase in orientation which is corroborated by the model. Atomic force microscopy and scanning electron microscopy show the evolution of the surface morphology and microstructure with changing processing conditions. Increased surface faceting is observed with increased dopant concentration and segregation as determined by X-ray photoelectron spectroscopy (XPS). There is also a clear correlation between the deposition conditions and the ferroelectric response, with increased electrical breakdown for DC sputtered films compared to RF sputtering and pulsed laser deposition. Overall, these results illustrate that the ferroelectric properties highly sensitive to the growth conditions and resulting microstructure.