Fermi Level Tuning by Low Temperature Atomic Layer Deposition/Epitaxy (ALD/ALE) of Ternary Chalcogenide Layers

原子层沉积（ald）是沉积碲基三元硫系层的首选合成技术。本文将研究（Sb1-xBix）2Te3、（GeTe）1-x(Sb2Te3)x和（GeTe）1-x(Bi2Te3)x三种硫族化合物体系，优化其组成因子x以使狄拉克锥中的费米能量水平，从而实现低载流子浓度和零塞贝克系数。对于后一物理量，将利用霍尔-塞贝克测量平台，该平台具有通过施加电场调节费米能级的附加能力。三元层将通过ALD工艺在合适的非晶和单晶衬底上在相当低的温度（RT至150'C）下合成。我们将研究衬底的影响(无定形二氧化硅与单晶衬底，如。GaAs和BaF2对层状形貌、能带结构和拓扑输运性质的影响。为了抑制反位缺陷，碲蒸气下的退火被整合到合成过程中，尽管理想的化学计量组成是通过低t A LD工艺以及使用合适的（活性的）金属有机前驱体来实现的。为了实现理想的ALD工艺，开发和测试特定的挥发性但热稳定（可储存）的金属有机前体是一个重要的项目目标，这将由来自埃森的Schulz小组为Bi2Te3， Sb2Te3和GeTe等二进制化合物解决。合成了一般类型（R3Si）2Te （R = Me, Et, i-Pr, Ph，…）的硅基取代碲，它很容易与M(OR')x型的锑和铋烷氧化物以及M(NR'2)x （M = Sb, Bi; x = 3; M = Ge, x = 2； R' = Me, Et, n-Pr, n-Bu, i-Pr, i-Bu, t- bu）的酰胺反应，随后由于形成热力学稳定的Si-N或Si-O键，硅基酰胺R3SiNR‘2或硅基醚R3SiOR’消去。有机取代基R和R‘的变化允许对热稳定性进行微调，因此适合于不分解储存（R， R’ = Me, Et, n-Pr, i-Pr）。此外，化合物的蒸汽和升华压力（挥发性）以及反应性在很大程度上取决于有机基团的空间大小（动力学稳定性）。基于优化的二元半导体ALD工艺，来自汉堡的Nielsch团队将通过交替应用二元工艺来优化三元体系的拓扑特性，并进行所有主要的物理表征（如上所述）。

Atomic Layer Deposition(A LD) is the synthesis technique of choice for the deposition of telluride based ternary chalcogenide layers. Three chalcogenide systems,( Sb1-xBix)2Te3, (Ge Te)1-x(Sb2Te3)x and (GeTe)1-x(Bi2Te3)x) will be investigated for which the composition factor x will be optimized in order to level the Fermi energy in the Dirac cone, thus achieving a low carrier concentration and a zero Seebeck coefficient. For the latter physical quantity a Hall-Seebeck measurement platform with the additional capability for tuning the Fermi energy level by applying electric field will be utilized. The ternary layers will be synthesized by ALD processes on suitable amorphous and single-crystalline substrates at rather low temperatures (RT to 150'C). We will study the substrate influence (amorphous silica versus single-crystalline substrates like e .g. GaAs and BaF2) on the layer morphology band structure and topologic transport properties. For the suppression of antisite defects, the annealing under tellurium vapor is integrated in the synthesis procedure, although the ideal stoichiometric composition is achieved by the low-T A LD processes as well as the use of suitable (reactive) metal organic precursors. For achieving ideal ALD processes, the development and testing of specific volatile but thermally stable (storable) metal-organic precursors is one essential project goal, which will be addressed by the Schulz group from Essen for binary compounds such as Bi2Te3, Sb2Te3 and GeTe. Silyl- substituted telluranes of the general type (R3Si)2Te (R = Me, Et, i-Pr, Ph, …) are synthesized, which readily react with either antimony and bismuth alkoxides of the type M(OR')x and amides M(NR'2)x, (M = Sb, Bi; x = 3; M = Ge, x = 2; R' = Me, E t , n-Pr, n-Bu, i-Pr , i-Bu, t-Bu) with subsequent elimination of silylamides R3SiNR'2 or silylethers R3SiOR' due to the formation of thermodynamically stable Si-N or Si-O bonds. Variation of the organic substituents R and R' allows the fine-tuning of the thermal stability, hence the suitability for decomposition-free storage( R, R' = Me, Et, n-Pr, i-Pr). Moreover, the vapor and sublimation pressure (volatility) as well as reactivity of the compound significantly depends on the steric size of the organic group (kinetic stabilization). Based on the optimized ALD processes for binary semi-conductors the Nielsch group from Hamburg will optimize the topological properties of ternary systems by alternating applications of binary processes and carry out all major physical characterization (mentioned above).