掺硼硅中由带载子和束缚掺杂光电离产生的高次谐波
Higher-harmonic generation in boron-doped silicon from band carriers and bound-dopant photoionization
摘要：
我们研究了Si：B中的超快谐波产生（HG），在4 K和300 K下，由强泵浦脉冲驱动，场达到~100 kV/cm，载波频率为300 GHz。我们报告了几个新的发现有关的非线性载流子动力学在强亚太赫兹领域。(i)在室温下观察到n=9阶的谐波，而在低温下，我们甚至可以分辨n=13的谐波。在中等场强下每个电荷载流子的磁化率与石墨烯中的载流子一样高，石墨烯被认为是具有最强亚太赫兹非线性响应的材料之一。(ii)对于T=300 K，其中结合到受体的载流子被完全热电离到价电子带中，磁化率值随着场强的增加而减小。结合多价带蒙特卡罗和时域有限差分（FDTD）传播的模拟表明，在这里，HG过程变得越来越占主导地位的能量依赖的散射率的贡献从带非抛物线，由于光学声子发射的发病，这最终导致在高场饱和。(iii)在T=4 K，其中大部分的电荷被绑定到受体，我们观察到的HG产量急剧上升的内部泵场为30 kV/cm，作为一个达到阈值的隧道电离。我们解开HG的贡献，在这种情况下，从最初的“代”和随后的带非线性的贡献，并表明，散射严重退化的任何相干性的空穴在随后的振荡。
英文摘要：
We investigate ultrafast harmonic generation (HG) in Si:B, driven by intense pump pulses with fields reaching ~100 kV/cm and a carrier frequency of 300 GHz, at 4 K and 300 K, both experimentally and theoretically. We report several novel findings concerning the nonlinear charge carrier dynamics in intense sub-THz fields. (i) Harmonics of order up to n=9 are observed at room temperature, while at low temperature we can resolve harmonics reaching even n=13. The susceptibility per charge carrier at moderate field strength is as high as for charge carriers in graphene, considered to be one of the materials with the strongest sub-THz nonlinear response. (ii) For T=300 K, where the charge carriers bound to acceptors are fully thermally ionized into the valence subbands, the susceptibility values decrease with increasing field strength. Simulations incorporating multi-valence-band Monte-Carlo and finite-difference-time-domain (FDTD) propagation show that here, the HG process becomes increasingly dominated by energy-dependent scattering rates over the contribution from band non-parabolicity, due to the onset of optical-phonon emission, which ultimately leads to the saturation at high fields. (iii) At T=4 K, where the majority of charges are bound to acceptors, we observe a drastic rise of the HG yields for internal pump fields of 30 kV/cm, as one reaches the threshold for tunnel ionization. We disentangle the HG contributions in this case into contributions from the initial 'generational'- and subsequent band-nonlinearities, and show that scattering seriously degrades any coherent recollision during the subsequent oscillation of the holes.
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