Charge Carrier Dynamics and Light Emission in Materials from First Principles

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• Marco Bernardi - Caltech
• Monday 10 April 2017, 14:00-15:00
• Rayleigh Seminar Room - Maxwell centre.

If you have a question about this talk, please contact Giorgio Divitini.

Experiments probing charge carrier transport and ultrafast dynamics are used broadly for characterizing materials and devices. Yet, their interpretation is often heuristic, and the understanding of the relevant carrier scattering mechanisms is incomplete. We will discuss advances in first-principles calculations that are providing new microscopic insight into carrier dynamics and light emission in materials. The talk will highlight theoretical and computational approaches we recently developed, focusing on case studies of interest for energy applications, including: 1) The main source of energy loss in most inorganic solar cells, namely, the ultrafast thermalization of excited (so-called “hot”) carriers that follows sunlight absorption. We compute the time and length scale over which hot carriers lose energy in silicon, and suggest strategies for extracting hot carriers and avoiding thermalization losses. 2) Ultrafast carrier dynamics and transport in polar materials, such as GaAs and GaN, for which we can accurately predict the temperature-dependent mobility and microscopically interpret time-resolved pump-probe measurements. In GaN, we find an asymmetry between the dynamics of excited electrons and holes, and analyze its implications for the efficiency of GaN light emitting devices. 3) Two-dimensional semiconductors, such as MoS2 and related transition metal dichalcogenides (TMDCs), which are promising for ultrathin solar cells and lighting devices. We focus on our recent calculations of light absorption and exciton radiative lifetimes in TMD Cs, and discuss recent experiments and challenges for theory. Our ongoing project to develop a first-principles code for computing carrier dynamics in complex materials will be discussed.

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