Extreme polarisation gradients (Akronym: „Polrock“): surface and interface analytics on rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-based heterostructures

在该项目中，将外延生长rS-ScxAl1-xN/wz-GaN-和rS-SCN/wz-ScxAl1-xN基异质结，并研究它们的界面性质。我们的目的是证明理论预测的极端极化梯度和极化诱导的片层电荷密度在不同晶体结构之间的界面。此外，它们应该以受控的方式进行调整，以便在电子和光学设备中应用。ScxAl1-xN-层和纤锌矿结构的GaN或ScxAl1-xN层(可以沿[0001]方向表现出很高的极化：Pmax(Wz)~1，4C/m2)在一个伪晶异质结构中具有岩盐结构(无极化，P(Rs)=0)和GaN或ScxAl1-xN层的新组合，使得能够获得非常高的极化梯度(∆P=Pmax(Wz))和极化感生的片层电荷密度，最高可达σ/e~8×10^14 cm-2。这些片状电荷密度比限制在假象GaAlN/GaN异质结界面的片状电荷密度高出约两个数量级，这符合最新的技术水平。为了通过实验上可测量的载流子分布来证明极端的极化梯度，有必要对带边分布进行模拟。他们需要关于能带不连续性、表面电势和掺杂的精确知识。分析能带不连续性和特定的表面和界面特性需要对单层及其异质结构进行详细的分析。在优化的氮极性和金属极性涂层和膜层体系的基础上，我们将确定ScxAl1-xN材料体系的结构和电子性质，以及Sc-含量对能带跃迁和声子的色散的影响。模拟将支持电子和声子能带结构的准确确定。所获得的洞察力将有助于证明rS-ScxAl1-xN/wz-GaN-和rS-SCN/wz-ScxAl1-xN-异质结界面的能带不连续性、能带弯曲和载流子分布，并使极端极化梯度及其受控变化的验证成为可能。

Within the project, rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-based heterostructures will be epitaxially grown, and their interface properties will be investigated. We aim to prove the theoretically predicted extreme polarization gradients and polarization-induced sheet charge densities at the interface between different crystal structures. Furthermore, they should be adjusted in a controlled manner for applications in electronic and optical devices. The novel combination of ScxAl1-xN-layers with rock salt structure (without polarization, P(rs) = 0) and GaN or ScxAl1-xN layers with wurtzite structure (which can show very high polarization along the [0001]-direction: Pmax(wz) ~~ 1,4 C/m2 ) within one pseudomorphic heterostructure, enables to achieve very high polarization gradients (∆P = Pmax(wz)) and polarization induced sheet charge densities up to σ/e ~~ 8 x10^14 cm-2. These sheet charge densities are about two orders of magnitude higher than sheet charges confined at interfaces of pseudomorphic GaAlN/GaN-heterostructures, which correspond to state-of-the-art. Simulations of band edge profiles are necessary to prove extreme polarization gradients by experimentally measurable charge carrier profiles. They need precise knowledge about band discontinuities, surface potentials, and doping. Analyzing band discontinuities and specific surface and interface properties requires a detailed analysis of the single layers and their heterostructures. Based on optimized nitrogen- and metal-polar coatings and layer systems, we will determine the structural and electronic properties of the ScxAl1-xN-material system and the dispersion of the band transitions and phonons in dependence of the Sc-content. Simulations will support the exact determination of the electronic and phonon band structure. The gained insight will help prove the band discontinuities, band bending, and charge carrier profiles at the interfaces of rs-ScxAl1-xN/wz-GaN- and rs-ScN/wz-ScxAl1-xN-heterostructures and enable the validation of extreme polarization gradients and their controlled variation.