Disruptive development of van der Waals semiconductors by enabling anion-controlled functionalities

2021-2022年半导体制造危机的影响凸显了现代社会对半导体技术的依赖程度。半导体是英国经济的重要组成部分，2020年的市场价值约为80亿美元，而且仍在增长。半导体是电子和光电子器件的基本组成部分，因此在许多看似无关的技术的进步中发挥着关键作用，例如微电子领域，可再生能源领域和通信领域。由于现代设备不断增加且经常相互冲突的要求，硅等传统半导体正被推向其物理极限的边缘。范德华半导体（vdW）和相关的二维材料（2D）可以为这些挑战提供解决方案，因为它们能够克服影响传统半导体的一些物理限制。这项EPSRC新研究者奖将通过设计具有新的和改进的功能的混合阴离子vdW半导体，以及可扩展的沉积方法来生产它们，来支持英国半导体部门的发展。vdW半导体的主要例子是黑磷（BP）或过渡金属二硫化物（TMDs）。大多数vdW材料要么是金属的，要么是绝缘的。只有少数化学家族，如BP或tmd具有半导体性质，可以剥离成二维形式。这限制了这些化学物质中可用的功能。如果我们利用多种阴离子的特性来设计具有新功能的新材料，那么vdW半导体中可用的各种功能可以大大增加。这最近在CrSBr中得到了证明，CrSBr是一种罕见的二维铁磁半导体。我将进一步发展这一领域，设计新的混合阴离子vdW半导体，属于金属硫卤化物和金属氧卤化物家族，具有高载流子迁移率，非线性光学性质和室温铁电性。为了提高这些材料的可制造性，我将修改聚合物辅助沉积（PAD）方法，使其能够同时插入多个阴离子。这种方法具有可扩展性和成本效益，因此适合快速跨越技术准备水平（TRL）规模走向工业化。PAD方法也将在允许化学灵活性设计具有目标性能的材料方面发挥关键作用，该材料基于所加入阴离子的独特物理和化学特性。例如，在氧化卤化物中，卤化物的选择将决定材料基本带隙的大小，从而决定材料吸收或发射不同部分可见光的能力。这使得基于插入的阴离子对材料属性进行原子控制成为可能。这些材料与半导体工业的相关性将最终通过制造电流整流器件（例如，pn结）来证明，其性能必须等于或优于工业标准硅。

Repercussions of the semiconductor manufacturing crisis in 2021-2022 have highlighted how much modern society depends on semiconductor technologies. Semiconductors are an important part of the UK economy, with a market worth around $8bn in 2020 and still on the rising. Semiconductors are fundamental components of electronic and optoelectronic devices thus playing a key-role in the advancement of a number of seemingly unrelated technologies such as the field of microelectronics, the renewable energy sector and the communication sector. Traditional semiconductors such as silicon are getting pushed to the edge of their physical limits by the constantly increasing and often conflicting requirements of modern devices. van der Waals (vdW) semiconductors and related two-dimensional materials (2D) can provide a solution to these challenges due their ability to overcome some of the physical limitations affecting traditional semiconductors.This EPSRC New Investigator Award will support the growth of the UK semiconductor department by designing mixed-anions vdW semiconductors with new and improved functionalities, and a scalable deposition method to produce them. Prime example of vdW semiconductors are black phosphorous (BP) or transitional metal dichalcogenides (TMDs). Most vdW materials are either metallic or insulating. Only few chemical families, such as BP or TMDs possess semiconducting properties and can be exfoliated to 2D form. This limits the functionalities that can be accessed to those available in these chemistries. The variety of functionalities available in vdW semiconductors can be drastically increased if we leverage the properties of multiple anions to design new materials with new functionalities. This was recently demonstrated for CrSBr, a rare case of 2D ferromagnetic semiconductor. I will further advance this field by designing new mixed-anion vdW semiconductors belonging to the family of metal chalcohalides and metal oxyhalides that display high mobility of the electrical carriers, non-linear optical properties and room temperature ferroelectricity. To boost the manufacturability of these materials, I will modify the Polymer Assisted Deposition (PAD) method to enable simultaneous insertion of multiple anions at once. This method is scalable and cost-effective, thus suitable to rapidly move across the technology readiness levels (TRL) scale towards industrialization. The PAD method will also be pivotal in allowing the chemical flexibility to design materials with targeted properties based on the unique physical and chemical properties of the incorporated anions. For example, in oxyhalides, the choice of the halide will determine the size of the material's fundamental band gap, determining the material's ability to absorb or emit a different portion of visible light. This enables an atomic control over the materials' properties based on the anion inserted. The relevance of these materials for the semiconductor industry will be finally demonstrated by fabricating current rectifying devices (e.g., p-n junctions), whose properties must be equal or superior to those of the industrial standard, silicon.