Sadasivam Sridhar, Chan Maria K Y, Darancet Pierre
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Phys Rev Lett. 2017 Sep 29;119(13):136602. doi: 10.1103/PhysRevLett.119.136602. Epub 2017 Sep 27.
We compute the transient dynamics of phonons in contact with high energy "hot" charge carriers in 12 polar and nonpolar semiconductors, using a first-principles Boltzmann transport framework. For most materials, we find that the decay in electronic temperature departs significantly from a single-exponential model at times ranging from 1 to 15 ps after electronic excitation, a phenomenon concomitant with the appearance of nonthermal vibrational modes. We demonstrate that these effects result from slow thermalization within the phonon subsystem, caused by the large heterogeneity in the time scales of electron-phonon and phonon-phonon interactions in these materials. We propose a generalized two-temperature model accounting for phonon thermalization as a limiting step of electron-phonon thermalization, which captures the full thermal relaxation of hot electrons and holes in semiconductors. A direct consequence of our findings is that, for semiconductors, information about the spectral distribution of electron-phonon and phonon-phonon coupling can be extracted from the multiexponential behavior of the electronic temperature.
我们使用第一性原理玻尔兹曼输运框架，计算了12种极性和非极性半导体中与高能“热”电荷载流子接触的声子的瞬态动力学。对于大多数材料，我们发现电子激发后1到15皮秒的时间范围内，电子温度的衰减显著偏离单指数模型，这种现象与非热振动模式的出现相伴。我们证明，这些效应是由声子子系统内的缓慢热化引起的，这是由这些材料中电子-声子和声子-声子相互作用时间尺度的巨大不均匀性导致的。我们提出了一个广义双温模型，将声子热化视为电子-声子热化的一个限制步骤，该模型捕捉了半导体中热电子和热空穴的完整热弛豫过程。我们的发现的一个直接结果是，对于半导体，可以从电子温度的多指数行为中提取有关电子-声子和声子-声子耦合光谱分布的信息。
