Carrier relaxation and lattice heating dynamics in silicon revealed by femtosecond electron diffraction
Carrier relaxation and lattice heating dynamics in silicon revealed by femtosecond electron diffraction
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DOI：
10.1021/jp064649n
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发表时间：
2006-12-21
影响因子：
3.3
通讯作者：
Miller, R. J. Dwayne
中科院分区：
文献类型：
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作者：
Harb, Maher;Ernstorfer, Ralph;Miller, R. J. Dwayne
我们报道了利用飞秒电子衍射来解析硅中电子-声子弛豫的动力学。在吸收5.6 mJ/cm(2)的387 nm光(对应于载流子密度为2.2 x 10（21) cm(-3)）下，将纳米多晶硅独立膜激发至损伤阈值以下。衍射图样在一定的延迟时间范围内被捕获，时间分辨率为350秒。所有检测到的布拉格峰都表现出时间常数小于2ps的强度损失。除了初始衰减之外，衍射强度在700ps以下没有进一步变化。我们发现，衍射阶的强度损失是由德拜-沃勒效应在时间尺度上解释的，这表明是热驱动过程，而不是电子驱动过程。此外，弛豫时间常数与激发态一致，在激发态中，由于载流子筛选，声子发射率降低。
We report on the use of femtosecond electron diffraction to resolve the dynamics of electron-phonon relaxation in silicon. Nanofabricated free-standing membranes of polycrystalline silicon were excited below the damage threshold with 387 nm light at a fluence of 5.6 mJ/cm(2) absorbed (corresponding to a carrier density of 2.2 x 10(21) cm(-3)). The diffraction pattern was captured over a range of delay times with a time resolution of 350 fs. All of the detected Bragg peaks exhibited intensity loss with a time constant of less than 2 ps. Beyond the initial decay, there was no further change in the diffracted intensity up to 700 ps. We find that the loss of intensity in the diffracted orders is accounted for by the Debye-Waller effect on a time scale indicative of a thermally driven process as opposed to an electronically driven one. Furthermore, the relaxation time constant is consistent with the excitation regime where the phonon emission rate is reduced due to carrier screening.