Cooling of photoexcited carriers in graphene by internal and substrate   phonons
  We investigate the energy relaxation of hot carriers produced by photoexcitation of graphene through coupling to both intrinsic and remote (substrate) surface polar phonons using the Boltzmann equation approach. We find that the energy relaxation of hot photocarriers in graphene on commonly used polar substrates, under most conditions, is dominated by remote surface polar phonons. We also calculate key characteristics of the energy relaxation process, such as the transient cooling time and steady state carrier temperatures and photocarriers densities, which determine the thermoelectric and photovoltaic photoresponse, respectively. Substrate engineering can be a promising route to efficient optoelectronic devices driven by hot carrier dynamics. 
Tony Low, Vasili Perebeinos, Raseong Kim, Marcus Freitag and Phaedon   Avouris
cond-mat.mes-hall