Unravelling the polarity preference and effects of the electrode layer on wurtzite aluminum nitride for piezoelectric applications

Aluminum nitride (AlN) is a promising material for electromechanical and optoelectronic applications due to its exceptional properties. The stability and control of the polarity of AlN surfaces, as well as the interactions between AlN and electrode layers, are critical for optimizing device performance. In this study, we investigate the properties of electrode layers on AlN slabs and their impact on the stability and polarity preferences of AlN surfaces. Using first principles simulations, we calculate the formation energies of various electrode layers on AlN slabs and analyze the resulting trends. Additionally, we examine the Bader charges of the electrode layers to gain insights into the nature of the interface interactions. Our findings reveal that the interaction between the electrode layer and the AlN slab is thermodynamically favorable and is mainly electrostatic or ionic in nature. The preferred stacking sequence of the electrode layer elements on Al-polar AlN slabs aligns with the overall wurtzite structure of the AlN slabs, minimizing lattice distortion and destabilization. The variation in the Born effective charge of the interfacial atoms on AlN slabs with electrode layer elements of different electronegativities could impact the interface polarization and piezoelectric properties. By considering electronegativity or Bader charges of the electrodes, the design of stable electrodes on AlN slabs with preferred polarity can be achieved. This study provides valuable insights into the design and optimization of AlN-based electronic and piezoelectric devices. Through careful consideration of the electronegativity of the electrodes, we can design stable electrodes tailored for aluminum nitride (AlN) slabs of desired polarity.