Photoexcited carrier dynamics and impact-excitation cascade in graphene

In materials with strong electron-electron interactions, photoexcitation can trigger a cascade in which multiple particle-hole excitations are generated. Here we analyze the cascade of impact-excitation processes in graphene in which many hot carriers are generated by a single absorbed photon. We show that the number of generated carriers has a strong dependence on doping (gate tunability). Linear scaling with photon energy is predicted for the number of pairs and for the duration of the cascade. These dependencies, along with a sharply peaked angular distribution of excited carriers, provide clear experimental signatures of hot carrier multiplication.