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

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.