Ferroelectricity in boron-substituted aluminum nitride thin films

This manuscript demonstrates ferroelectricity in B-substituted AlN thin films and a complementary set of first-principles calculations to understand their structure-property relationships. ${\mathrm{Al}}_{1--x}{\mathrm{B}}_{x}\mathrm{N}$ are grown by dual-cathode reactive magnetron sputtering on $(110)\mathrm{W}/(001){\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates at 300\ifmmode^\circ\else\textdegree\fi{}C compositions spanning $x=0$ $x=0.20$. X-ray diffraction studies indicate decrease both the $c$ $a$ lattice parameters with increasing B concentration, resulting unit cell volume constant $c$/$a$ axial ratio 1.60 over this composition range. Films $0.02\ensuremath{\le}x\ensuremath{\le}0.15$ display ferroelectric switching remanent polarizations exceeding $125\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--2}$ while maintaining band gap energies $>5.2\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The large allows low frequency hysteresis measurement (200 Hz) modest leakage contributions. At concentrations $x>0.15$, $c$-axis orientation deteriorates behavior is degraded. Density-functional theory corroborate structural observations provide predictions for wurtzite $u$ parameter, polarization reversal magnitudes, composition-dependent coercive fields.