Theory of coherent collective excitations in semiconductor superlattices excited by ultrashort optical pulses

超短光脉冲激发的半导体超晶格相干集体激发理论

基本信息

批准号：
14540297
负责人：
KATAYAMA Shin-ichi
金额：
$ 1.54万
依托单位：
Japan Advanced Institute of Science and Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

We have explored coherent oscillations in semiconductor superlattices (multiple quantum wells : MQWs) excited by ultrashort pulse lasers, and have studied generation mechanism of electromagnetic waves (including a laser) in a terahertz (THz) regime associated with the collective excitations. Our results are summarized as follows :(1)We have explored the coherent intra-miniband plasmon in a superlattice, which propagates along the growth axis. To compare our results with the observed THz radiation as well as reflective electro-optical sampling data, we have constructed a dielectric response theory based on density matrix. Using Kronig-Penney model, and changing ratio of well width to barrier width, we evaluated the plasmon dispersion relation. Our results indicate the discrete nature of plasma frequency as a function of electron number in multi-minibands, and correspond well to the observed appearance and disappearance of THz radiation from AlGaAs/GaAs superlattices.(2)We simulated THz radiation by coherent LO phonons as well as ultrafast movements of non-equilibrium photoexcited carriers in GaAs p-i-n diodes under high electric field. So we revealed an importance of synchronization between LO phonon and overshoot of carriers for generation of coherent LO phonon oscillation, and have predicted a saturation behavior of THz radiation intensity under extremely strong electric fields above 150 kV/cm.(3)We have constructed a theory of THz Raman laser excited optically in asymmetric coupled double quantum wells (ACDQWs). A stimulated Stokes Raman scattering due to collective inter-subband plasm on produces the proper laser gain in this structure. Further, it was revealed that the interaction of coherent intersubband plasmon with LO phonons plays the key role for a determination of the laser frequencies. Our results explain well the observed laser frequency in AlGaAs/GaAs ACDQWs.

我们已经探索了超时脉冲激光器激发的半导体超晶格（多个量子井：MQW）中的连贯振荡，并研究了与集体激发相关的Terahertz（THZ）中电磁波（包括激光）的发电机理（包括激光）。我们的结果总结如下：（1）我们探索了超晶格中的连贯的米支木内等离子体，从而沿着生长轴传播。为了将我们的结果与观察到的THZ辐射以及反射性电流采样数据进行比较，我们基于密度矩阵构建了介电响应理论。使用Kronig-Penney模型，以及井宽与屏障宽度的变化，我们评估了等离子分散关系。我们的结果表明，等离子体频率与多中心中电子数的函数的离散性质，并且很好地对应于观察到的外观和从藻类/GAAS超晶格的THz辐射的外观和消失。（2）我们通过相干LO Phonons模拟THZ辐射，并通过非equilibribribim photoexibrium Photoexibrium Photoexexpuith fired Fielter Fielter Fielter high high high high high high high high high high high high high high ind dii。因此，我们揭示了载体和载体过冲之间同步的重要性，即产生相干的声音振荡，并预测了在高于150 kV/cm的极强电场下，Thz辐射强度的饱和行为。（3）我们已经构建了Thz Raman激发型在As -Memmetric Coupled Coupled Coupled Doubled Coupled coupled Coupled Coupled doubled doubled doubled Coupled plouss（ACD）的理论（ACD）。刺激的stok刺激了由于集体间间比带引起的拉曼散射，从而在该结构中产生适当的激光增益。此外，据揭示了相干间隔等离子体与LO声音的相互作用在确定激光频率的关键作用中。我们的结果很好地解释了观察到的激光频率在藻类/GAAS ACDQW中。