Dynamically coupled plasmon-phonon modes in GaP: An indirect-gap polar semiconductor
Dynamically coupled plasmon-phonon modes in GaP: An indirect-gap polar semiconductor
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DOI：
10.1103/physrevb.92.205203
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发表时间：
2015-11
影响因子：
3.7
通讯作者：
K. Ishioka;K. Brixius;U. Höfer;A. Rustagi;Evan M. Thatcher;C. Stanton;H. Petek
中科院分区：
文献类型：
--
作者：
K. Ishioka;K. Brixius;U. Höfer;A. Rustagi;Evan M. Thatcher;C. Stanton;H. Petek
通过实验和理论研究了间接带隙半导体GaP中相干光学声子和光生电子空穴等离子体的超快耦合动力学。对于 800 nm 光的带隙以下激发和探测，仅观察到裸露的纵向光学 (LO) 声子。对于 400 nm 光的间隙激发，光激发产生高密度、非平衡 e-h 等离子体，由于 LO 声子-等离子体耦合 (LOPC) 模式，引入了额外的、更快的衰减振荡。 LOPC 模式频率对于 n 和 p 掺杂 GaP 表现出非常相似的行为，随着光激发载流子密度的增加，从 LO 下移到横向光学 (TO) 声子频率极限。我们将 LOPC 模式分配给与光激发多组分等离子体耦合的 LO 声子。对于 400 nm 激发，大部分光激发电子在 30 fs 内从谷散射到卫星 X 谷，而轻空穴和自旋分裂空穴则散射到重空穴带中。由此产生的混合等离子体被强烈阻尼，导致 LOPC 频率出现在剩余斯特拉伦间隙中。由于 X 电子和重空穴的有效质量较大，耦合模式在载流子密度为 5 × 1018 cm−3 时表现得最为明显。我们对超短光脉冲激发后的核运动和电子极化进行理论计算，以获得耦合模式的瞬态反射率响应。我们发现，虽然光激发载流子的纵向扩散微不足道，但应考虑由于激光强度分布而导致的光激发载流子的横向不均匀性，以重现所观察到的耦合模式动力学的主要特征。
The ultrafast coupling dynamics of coherent optical phonons and the photoexcited electron-hole plasma in the indirect gap semiconductor GaP are investigated by experiment and theory. For below-gap excitation and probing by 800-nm light, only the bare longitudinal optical (LO) phonons are observed. For above-gap excitation with 400-nm light, the photoexcitation creates a high density, nonequilibrium e-h plasma, which introduces an additional, faster decaying oscillation due to an LO phonon-plasmon coupled (LOPC) mode. The LOPC mode frequency exhibits very similar behavior for both nand p-doped GaP, downshifting from the LO to the transverse optical (TO) phonon frequency limits with increasing photoexcited carrier density. We assign the LOPC mode to the LO phonons coupled with the photoexcited multicomponent plasma. For the 400-nm excitation, the majority of the photoexcited electrons are scattered from the valley into the satellite X valley, while the light and spin-split holes are scattered into the heavy hole band, within 30 fs. The resulting mixed plasma is strongly damped, leading to the LOPC frequency appearing in the reststrahlen gap. Due to the large effective masses of the X electrons and heavy holes, the coupled mode appears most distinctly at carrier densities 5 × 1018 cm−3. We perform theoretical calculations of the nuclear motions and the electronic polarizations following an excitation with an ultrashort optical pulse to obtain the transient reflectivity responses of the coupled modes. We find that, while the longitudinal diffusion of photoexcited carriers is insignificant, the lateral inhomogeneity of the photoexcited carriers due to the laser intensity profile should be taken into account to reproduce the major features of the observed coupled mode dynamics.