In this study, we demonstrate ferroelectricity in high-quality monocrystalline quaternary alloy ScAlGaN. Sc0.2Al0.45Ga0.35N films are grown by plasma-assisted molecular beam epitaxy and exhibit a surface roughness of 0.5 nm, limited by the roughness of the underlying molybdenum template. Polarization-electric field and positive-up-negative-down measurements reveal unambiguous ferroelectric switching with a coercive field of ∼5.5 MV cm−1 at 10 kHz and high remanent polarization of ∼150 μC cm−2. Time-dependent measurements suggest that the polarization reversal behavior adheres to the Kolmogorov–Avrami–Ishibashi model and follows a scheme of domain nucleation and growth. Detailed piezoresponse force microscopy studies further elucidate the evolution of polarity reversal domains in wurtzite nitride ferroelectrics and support the notion that the growth of inversion domains occurs via an in-plane motion of the domain walls. The realization of functional ferroelectric quaternary alloys in the wurtzite nitride family extends beyond being a technical demonstration. The additional degree of bandgap, band alignment, lattice parameter, and piezoelectric constant tunability achievable through quaternary alloys unveils a vast dimension through which wurtzite nitride ferroelectrics can be optimally engineered for a broad variety of high-performance electronic, optoelectronic, and acoustic devices and systems.

中文翻译：

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铁电四元合金Sc0.2Al0.45Ga0.35N的分子束外延及表征

在这项研究中，我们展示了高质量单晶四元合金 ScAlGaN 的铁电性。 Sc0.2Al0.45Ga0.35N 薄膜通过等离子体辅助分子束外延生长，表面粗糙度为 0.5 nm，但受到底层钼模板粗糙度的限制。极化电场和正上负下测量揭示了明确的铁电开关，在 10 kHz 时具有~5.5 MV cm−1 的矫顽场和~150 μC cm−2 的高剩余极化。与时间相关的测量表明，极化反转行为遵循 Kolmogorov-Avrami-Ishibashi 模型，并遵循域成核和生长的方案。详细的压响应力显微镜研究进一步阐明了纤锌矿氮化物铁电体中极性反转域的演化，并支持了反转域的生长通过域壁的面内运动发生的观点。在纤锌矿氮化物家族中实现功能性铁电四元合金不仅仅是技术演示。通过四元合金可实现更高程度的带隙、能带排列、晶格参数和压电常数可调性，揭示了纤锌矿氮化物铁电体可以优化设计用于各种高性能电子、光电和声学器件和系统的广阔空间。 。