Bhattarai Bipin, Zhang Xiaoman, Xu Wangwang, Gu Yijia, Meng W J, Meng Andrew C
Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA.
Department of Mechanical and Industrial Engineering, Louisiana State University, Baton Rouge, LA 70803, USA.
Mater Horiz. 2024 Oct 28;11(21):5402-5408. doi: 10.1039/d4mh00551a.
While aluminum scandium nitride based ferroelectric materials have shown significant promise for non-volatile memory applications, difficulties relating challenges in device performance, such as electrical leakage, to structural characteristics motivate improved understanding of the fundamental structure-property relationship. Spinodal decomposition has been reported in this material system, consistent with our observation of compositional segregation in AlScN films grown by reactive sputter epitaxy. To better understand the effects of spatially non-uniform Sc concentrations, the electronic and ferroelectric (FE) properties of AlScN as a function of Sc distribution are studied using density functional theory (DFT). We explore the impact of Sc-rich atomic planes in wurtzite AlScN with Sc concentration ranging from 0 to 44 at% through a supercell approach. We find that while spontaneous polarization decreases with Sc concentration (∼133 to 102 μC cm), periodic Sc-rich planar clusters slow this effect, suggesting that phase segregation counters the effects of increasing Sc composition. Furthermore, the FE switching barrier per formula unit (f.u.) as a function of composition exhibits a local maximum of 0.60 eV f.u. at 25% Sc concentration in the presence of Sc-rich planes but decreases monotonically (0.51 to 0.28 eV f.u.) if Sc is uniformly distributed, suggesting that the spatial distribution of Sc plays an important role in the optoelectronic properties of the material by changing the energy landscape. Sc clustering also decreases the bandgap of the material. This study shows that the structural complexity arising from spatial composition modulation provides tunability of ferroelectric properties in AlScN ferroelectrics.
虽然基于氮化铝钪的铁电材料在非易失性存储器应用中显示出巨大潜力，但与器件性能挑战（如漏电）相关的困难与结构特征促使人们更好地理解基本的结构 - 性能关系。在这种材料体系中已报道有旋节分解现象，这与我们在通过反应溅射外延生长的AlScN薄膜中观察到的成分偏析一致。为了更好地理解空间上不均匀的钪浓度的影响，使用密度泛函理论（DFT）研究了AlScN作为钪分布函数的电子和铁电（FE）特性。我们通过超胞方法研究了纤锌矿型AlScN中钪浓度范围从0到44原子百分比的富钪原子平面的影响。我们发现，虽然自发极化随钪浓度降低（从约133降至102 μC/cm），但周期性的富钪平面簇减缓了这种效应，这表明相分离抵消了钪成分增加的影响。此外，每个化学式单位（f.u.）的铁电开关势垒作为成分的函数，在存在富钪平面的情况下，在25%钪浓度时表现出局部最大值0.60 eV/f.u.，但如果钪均匀分布则单调下降（从0.51降至0.28 eV/f.u.），这表明钪的空间分布通过改变能量态势在材料的光电特性中起重要作用。钪团簇也降低了材料的带隙。这项研究表明，由空间成分调制引起的结构复杂性为AlScN铁电体中铁电性能提供了可调节性。
