Magnetic Fields and Electric Potentials Steer Charge for Efficient Separation.

Researchers demonstrate control of charge carrier movement within planar structures by combining magnetic fields with engineered electric potentials. This manipulation facilitates efficient charge separation following photo-excitation, offering potential advancements in transport mechanisms and photoelectric/photovoltaic device design.

The efficient manipulation of charge carriers is central to advances in electronic and optoelectronic devices. Researchers are continually seeking methods to direct the flow of these carriers, particularly in two-dimensional materials like graphene, which offer unique electronic properties. A team at the Helmholtz-Zentrum Dresden-Rossendorf – Joris Josiek, Friedemann Queisser, Stephan Winnerl, and Ralf Schützhold – detail a theoretical approach to achieve precisely this control in their paper, ‘Magneto-photoelectric effect in graphene via tailored potential landscapes’. They demonstrate how a combination of magnetic fields and specifically engineered electric potentials can steer photo-generated charge carriers, potentially leading to improved designs for transport schemes and photoelectric/photovoltaic applications.

Directed Charge Carrier Control in Planar Materials

The precise manipulation of charge carriers within two-dimensional (2D) materials represents a notable development in materials science, with implications for electronic and optoelectronic devices. Recent research demonstrates the steering of photo-generated charge carriers using a combination of constant magnetic fields and spatially varying electric potentials, achieving efficient charge separation and enabling novel transport schemes.

This work builds upon decades of investigation into 2D materials, notably graphene and hexagonal boron nitride. These materials exhibit unique electronic properties stemming from their atomic-scale thickness and distinct band structures. Modifying these materials through doping – the intentional introduction of impurities – allows for refinement of conductivity and carrier density, providing a means to control charge carrier behaviour. Researchers utilise the formation of p-n junctions – interfaces between materials with differing charge carrier concentrations – within the planar material to create directed pathways for charge carrier movement and maximise separation efficiency.

The core of this approach involves applying an in-plane electric potential alongside a perpendicular magnetic field. This configuration generates a Lorentz force – a force exerted on a charged particle moving in a magnetic field – which deflects the moving charge carriers. By carefully shaping the electric potential, researchers direct these deflected carriers, achieving efficient charge separation, a critical process for photoelectric and photovoltaic devices. The design of these potential landscapes draws upon established theoretical understanding of electron behaviour in electric fields, including concepts from relativistic quantum electrodynamics, such as those originally explored by Sauter and Schwinger, which describe the behaviour of charged particles in strong fields.

Investigations focus on actively influencing charge carrier trajectories within planar materials subjected to these combined fields, offering a method for directed transport. The study demonstrates that carefully engineered electric potential landscapes effectively steer these carriers, potentially enhancing performance in various applications and validating the theoretical framework underpinning this approach.

Researchers are expanding the scope of this technique beyond graphene and hexagonal boron nitride, broadening its applicability. This includes investigating the potential for incorporating non-linear optical effects – where the material’s response to light is not proportional to the light’s intensity – or utilising time-varying potentials to dynamically control charge carrier movement. Detailed modelling and simulation, coupled with experimental validation, refine design parameters and enhance device performance.

Ongoing research focuses on optimising potential landscapes for specific device architectures, investigating the impact of material properties – such as carrier mobility (how easily charge carriers move through the material) and defect density – on charge transport, and exploring the scalability of this technique for large-area devices. This work establishes a foundation for developing advanced charge transport and energy conversion technologies, potentially leading to highly efficient and versatile electronic and optoelectronic devices.