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SUMMARY:Charge Carrier Dynamics and Light Emission in Materials from First
  Principles - Marco Bernardi - Caltech
DTSTART:20170410T130000Z
DTEND:20170410T140000Z
UID:TALK71977@talks.cam.ac.uk
CONTACT:Giorgio Divitini
DESCRIPTION:Experiments probing charge carrier transport and ultrafast dyn
 amics are used broadly for characterizing materials and devices. Yet\, the
 ir interpretation is often heuristic\, and the understanding of the releva
 nt carrier scattering mechanisms is incomplete. We will discuss advances i
 n first-principles calculations that are providing new microscopic\ninsigh
 t into carrier dynamics and light emission in materials.\nThe talk will hi
 ghlight theoretical and computational approaches we recently developed\, f
 ocusing on case studies of interest for energy applications\, including:\n
 1) The main source of energy loss in most inorganic solar cells\, namely\,
  the ultrafast thermalization of excited (so-called “hot”) carriers th
 at follows sunlight absorption. We\ncompute the time and length scale over
  which hot carriers lose energy in silicon\, and suggest strategies for ex
 tracting hot carriers and avoiding thermalization losses.\n2) Ultrafast ca
 rrier dynamics and transport in polar materials\, such as GaAs and GaN\, f
 or 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 dev
 ices.\n3) Two-dimensional semiconductors\, such as MoS2 and related transi
 tion metal dichalcogenides (TMDCs)\, which are promising for ultrathin sol
 ar cells and lighting devices. We focus on our recent calculations of ligh
 t absorption and exciton radiative lifetimes in TMDCs\, and discuss recent
  experiments and challenges for theory.\nOur ongoing project to develop a 
 first-principles code for computing carrier dynamics in complex materials 
 will be discussed.
LOCATION:Rayleigh Seminar Room - Maxwell centre
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