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

2021-2022年半导体制造业危机的爆发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年市场价值约为80亿美元，且仍在增长。半导体是电子和光电子设备的基本组成部分，因此在许多看似无关的技术（如微电子领域，可再生能源部门和通信部门）的发展中发挥着关键作用。传统半导体（如硅）正被现代设备不断增长且往往相互冲突的要求推向其物理极限的边缘。货车德瓦耳斯（vdW）半导体和相关的二维材料（2D）能够克服传统半导体的物理限制，为这些挑战提供解决方案。EPSRC新研究者奖将通过设计具有新功能和改进功能的混合阴离子vdW半导体，以及生产它们的可扩展沉积方法，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）或过渡金属二硫属化物（TMD）。大多数vdW材料是金属或绝缘的。只有少数化学家族，如BP或TMD具有半导体性质，可以剥离成2D形式。这限制了可以获得这些化学品中可用的那些功能。如果我们利用多种阴离子的性质来设计具有新功能的新材料，那么vdW半导体中可用的功能的种类可以急剧增加。这是最近证明了CrSBr，一种罕见的情况下，二维铁磁半导体。我将进一步推进这一领域的设计新的混合阴离子VDW半导体属于家庭的金属硫族卤化物和金属卤氧化物，显示高流动性的电载流子，非线性光学性能和室温铁电性。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，以便同时插入多种阴离子。这种方法是可扩展的和具有成本效益的，因此适合于快速跨越技术就绪水平（TRL）规模走向工业化。PAD方法也将是关键的，它允许化学灵活性，以基于所结合阴离子的独特物理和化学性质来设计具有目标性质的材料。例如，在卤氧化物中，卤化物的选择将决定材料的基本带隙的大小，决定材料吸收或发射不同部分可见光的能力。这使得能够基于插入的阴离子对材料的性质进行原子控制。这些材料对于半导体工业的相关性将最终通过制造电流整流器件（例如，p-n结），其特性必须等于或上级于工业标准硅。

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.