Realizing Giant Ferroelectricity in Stable wz-Al1-xBxN Alloys by Controlling the Microstructure and Elastic Constant

Abstract

The emerged wurtzite-type (wz) ferroelectric Al_1 − xB_xN alloys have drawn increasing attention due to superior ferroelectricity and excellent compatibility with microelectronics. Revealing and controlling the microstructure and ferroelectric origin is vital to design and fabricate stable wz-Al_1 − xB_xN alloy with giant ferroelectricity. We find that the β-BeO-like rather than h-BN-like structure is the non-polar intermediate phase in the polarization inversion process of stable wz-Al_1 − xB_xN alloy. The stability and ferroelectric switching pathway of wz-Al_1 − xB_xN alloy are dominated by the covalent bond strength and elastic constant C₁₄. Due to the reduced internal parameter u and enhanced C₁₄ of wz-Al_1 − xB_xN alloy, the spontaneous polarization and polarization switching barrier respectively raises and declines as the B concentration increases. Meanwhile, the spontaneous polarization is enlarged by the compression along horizontal direction and tension along c-axis direction, while the polarization switching barrier and band gap are reduced by the all the tension. Moreover, the polarization switching fields are lower than the breakdown fields of wz-Al_1 − xB_xN alloys with tension. As a result, the giant ferroelectricity with larger spontaneous polarization than wz-Al_1 − xSc_xN alloy and comparable polarization switching barrier to the common ferroelectric oxide is designed in for wz-Al_1 − xB_xN alloy. It should be noted that the phase transformation concentration of about 0.1875 for wz-Al_1 − xB_xN alloy is reduced by both tension and compression. These findings give a deeply understanding of ferroelectricity wz-Al_1 − xB_xN alloy, and provide a guideline to design high-performance ferroelectric wz-Al_1 − xB_xN alloys.