The importance of interband transitions on the ultrafast relaxation process in photoexcited pristine graphene is evaluated by means of an ensemble Monte Carlo simulator. Impact ionization and Auger recombination in the collinear limit are considered, together with phonon-induced generation and recombination and intraband scattering mechanisms. The results show that collinear impact ionization is dominant in the first 100 femtoseconds, creating an important excess carrier population that is finally eliminated in the picosecond scale, together with the photoexcited population, by Auger and optical phonon-assisted recombination. The hot phonon effect is also important, stimulating phonon absorption and indirectly reducing the net collinear recombination in the hundreds of femtosecond range. The substrate type is an important factor, appeasing collinear impact ionization via screening and creating additional cooling channels that speed up the relaxation process. The results evidence that interband collinear generation processes are critical to explain the fastest stages of the relaxation process in graphene.

借助集成蒙特卡罗模拟器评估了带隙跃迁对光激发原始石墨烯中超快弛豫过程的重要性。考虑了共线极限内的碰撞电离和俄歇复合，以及声子诱导的生成和复合以及带内散射机制。结果表明，共线碰撞电离在前100飞秒中占主导地位，产生了重要的过量载流子，该载流子最终在皮秒级被光子和光学声子辅助重组消除，并与光激发的电离一起。热声子效应也很重要，它可以刺激声子吸收并间接减少数百飞秒范围内的净共线复合。基材类型是一个重要因素，通过筛选并建立额外的冷却通道来加速共线碰撞电离，从而加快松弛过程。结果证明带间共线生成过程对于解释石墨烯弛豫过程的最快阶段至关重要。