Electromechanical losses in carbon- and oxygen-containing bulk AlN single crystals

• Published in: Solid state ionics 2019-12, Vol.343, p.115072, Article 115072
• Main Authors: Kogut, Iurii, Hartmann, Carsten, Gamov, Ivan, Suhak, Yuriy, Schulz, Michal, Schröder, Sebastian, Wollweber, Jürgen, Dittmar, Andrea, Irmscher, Klaus, Straubinger, Thomas, Bickermann, Matthias, Fritze, Holger
• Format: Article
• Language: English
• Subjects: Aluminum nitride; Anelastic relaxation of point defects; Anelasticity; Bulk acoustic wave resonator; Carbon; Crystal defects; Current carriers; Electric properties; Electrical resistivity; Electromechanical losses; Heat conductivity; High temperature; Impurities; Oxygen; Oxygen content; Piezoelectricity; Point defects; Single crystals
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2019.115072

Bulk single-crystalline aluminum nitride (AlN) is potentially a key component for low-loss high-temperature piezoelectric devices. However, the incorporation of electrically active impurities and defects during growth of AlN may adversely affect the performance of piezoelectric resonators especially at high temperatures. The electrical conductivity and electromechanical losses in bulk AlN single crystals are analyzed in the temperature range of 300–1200 K with respect to various contents of growth-related impurities in them. For AlN with [O]/[C] ≤ 1, an increase of electrical conductivity due to thermal activation of charge carriers in the temperature range of 850–1200 K has been observed and was determined to be a major contribution to electromechanical losses Q−1 rising up to maximum values of about 10−3 at 1200 K. As the oxygen content in AlN increased, the magnitude and the activation energy of high-temperature electrical conductivity increased. In oxygen-dominated AlN, two major thermally activated contributions to electromechanical losses were observed, namely, the anelastic relaxations of point defects at temperatures of 400–800 K and electrical conductivity at T > 800 K. •Electrical conductivity of AlN single crystals is investigated from 300 to 1200 K.•Resonant properties of AlN single crystals are investigated from 300 to 1200 K.•Electromechanical losses in AlN at medium and high temperatures are analyzed.•Anelastic features of electromechanical behavior of AlN resonators are discussed.