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首页> 外文学位 >Time-resolved second harmonic generation studies of carrier and carrier-phonon dynamics at gallium arsenide surfaces (Gallium arsenide).
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Time-resolved second harmonic generation studies of carrier and carrier-phonon dynamics at gallium arsenide surfaces (Gallium arsenide).

机译：时间分辨的二次谐波产生研究，研究砷化镓表面（砷化镓）上的载流子和载流子声子动力学。

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摘要

Carrier dynamics in the depletion region of GaAs(110) were studied using femtosecond time-resolved second-harmonic generation. Due to its short probing depth, SHG is ideally suited for Angstrom-scale sensitivity to carrier density near the surface. A modified one-dimensional drift and diffusion model that includes separate surface trap capture dynamics for electrons and holes was used to fit the data. Contrary to analysis using the ambipolar diffusion model, no significant surface, trap recombination was observed.; Surface physical changes (disorder/damage) due to femtosecond pulsed laser irradiation were observed in a new regime—extremely low laser fluence (10−3 of the single shot bulk damage fluence) and large number of laser shots (>109 pulses). Disorder of the (1 x 1)-relaxed GaAs(110) surface was monitored using SHG intensity and time-resolved SHG-based surface phonon spectroscopy. No bulk damage was detected during the laser irradiation. Disorder is reversible by thermal annealing at 580°C. A new mechanism for femtosecond laser-induced surface physical reactions is proposed. Disorder is caused by a surface dangling bond hole-induced lattice instability. On rare high density hole fluctuations the reaction barrier is lowered to ∼kBT. This is remarkably different from traditional thermal chemical reactions where the rate limiting process is rare vibrational fluctuations that overcome eV-scale reaction barriers.; The interband transition of the dangling bonds on the GaAs(110)-(1 x 1) relaxed surface was studied with a new time-domain technique based on SHG. Two TRSHG field intensities and their interference are used to deconvolve the laser pulse parameters from the coherent media response. In typical coherent electronic transition studies, strict “energy-conservation” within the electronic system requires that only transition frequencies that fall within the laser bandwidth may be driven coherently. Surprisingly, media oscillation frequencies several 100 meV outside the laser bandwidth were observed. This implies that the full quantum coherence of the electronic and other material systems must be considered. The large energy shift implies that the electronic system is coupled to electronic rather than phonon excitation. Possibilities include plasmon-polaritons, exchange interaction, or band gap renormalization. The large density of “incoherent” surface dangling bond holes needed for these effects would be driven to the surface by the depletion field.
机译：利用飞秒时间分辨的二次谐波产生研究了GaAs（110）耗尽区中的载流子动力学。由于探测深度短，SHG非常适合对表面附近的载流子密度进行埃级灵敏度测量。修改后的一维漂移和扩散模型包括对电子和空穴的单独表面陷阱捕获动力学，用于拟合数据。与使用双极性扩散模型进行分析相反，未观察到明显的表面陷阱陷阱复合。飞秒脉冲激光辐照导致的表面物理变化（无序/损坏）在一种新的状态下被观察到-极低的激光通量（单次批量损伤通量的<10 -3 ）和大量的激光射击（> 10 9 个脉冲）。使用SHG强度和时间分辨的基于SHG的表面声子光谱技术监测（1 x 1）松弛的GaAs（110）表面的无序。在激光照射期间未检测到整体损坏。通过在580°C下进行热退火，可逆失序。提出了一种飞秒激光诱导的表面物理反应的新机制。乱序是由表面悬空的键孔引起的晶格不稳定性引起的。在极少数的高密度空穴波动下，反应势垒降低到〜k B T。这与传统的热化学反应显着不同，在传统的热化学反应中，限速过程是罕见的振动波动，克服了eV级反应障碍。利用基于SHG的新时域技术研究了GaAs（110）-（1 x 1）弛豫面上悬挂键的带间跃迁。使用两个TRSHG场强及其干扰将激光脉冲参数从相干介质响应中解卷积。在典型的相干电子跃迁研究中，电子系统内严格的“节能”要求只有相干驱动落入激光带宽内的跃迁频率。令人惊讶地，观察到在激光带宽之外几百meV的介质振荡频率。这意味着必须考虑电子和其他材料系统的完整量子相干性。大的能量偏移意味着电子系统耦合到电子，而不是声子激发。可能性包括等离激元-极化子，交换相互作用或带隙重归一化。这些效应所需的大密度“非相干”表面悬空键合孔将由耗尽场驱动到表面。

著录项

  • 作者

    Chou, Keng-Chang.;

  • 作者单位

    University of California, Riverside.;

  • 授予单位 University of California, Riverside.;
  • 学科 Physics Condensed Matter.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 126 p.
  • 总页数 126
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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