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

原子层沉积(A LD)是沉积碲基三元硫化物薄膜的首选合成技术。研究了(Sb1-xBix)2Te3，(Ge Te)1-x(Sb2Te3)x和(GeTe)1-x(Bi2Te3)x三种硫系化合物，并对其组成因子x进行了优化，以使Dirac锥中的费米能趋于平坦，从而实现低载流子浓度和零Seebeck系数。对于后者的物理量，将使用霍尔-塞贝克测量平台，该平台具有通过施加电场来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到150℃)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，例如。GaAs和BaF2)对薄膜形貌、能带结构和拓扑输运性质的影响。为了抑制反位缺陷，在合成过程中集成了碲蒸气下的热处理，尽管通过低T-A LD工艺以及使用合适的(活性)金属有机前驱体可以获得理想的化学计量比组成。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，埃森的舒尔茨团队将针对Bi2Te3、Sb2Te3和GeTe等二元化合物解决这一问题。普通型(R3Si)2Te(R=Me，Et，i-Pr，Ph，…)的硅基取代碲烷它们很容易与M(OR‘)x型的锑和铋的醇氧化物和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)反应，随后由于形成热力学稳定的Si-N或Si-O键而消除了硅酰胺R3SiNr’2或硅醚R3SiOR‘。有机取代基R和R‘的变化允许热稳定性的微调，因此适合于无分解储存(R，R’=Me，Et，n-Pr，i-Pr)。此外，化合物的蒸气和升华压力(挥发性)以及反应活性显著取决于有机基团的空间大小(动力学稳定性)。来自汉堡的Nielsch小组将在优化的二元半导体ALD工艺的基础上，通过交替应用二元工艺来优化三元体系的拓扑性质，并执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).