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Carrier dynamics of semiconductor surfaces by means of femtosecond two-photon photoelectron spectroscopy

通过飞秒双光子光电子能谱研究半导体表面的载流子动力学

基本信息

批准号：
12440087
负责人：
TANIMURA Katsumi
金额：
$ 10.18万
依托单位：
OSAKA UNIV.
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

The purpose of this project is to elucidate the dynamics of excited states on semiconductor surfaces, a typical quasi-two dimensional system, by means of femtosecond two-photon photoelectron (2ppe) spectroscopy. The knowledge of the dynamics provides fundamental basis on which mechanisms of photoinduced structural changes on the surfaces can be understood from microscopic point of view. Main results obtained are summarized below.1) The femtosecond-time resolved studies of 2ppe on Si(001)-(2x1) has resolved fundamental processes of surface-state dynamics including the transitions from bulk-to-surface states and the depopulation of the surface states. One of the most important findings is that the transition rate from bulk-to-surface states is carrier-density dependent; the rate is proportional to squire of the density. Thus, an important role of electron-electron scattering in the transition process has been revealed for the first time.2) The photoinduced structural changes on Si(111)-(7x7), Si(001)-(2x1), Si(111)-(2x1), and InP(110)-(1x1)surfaces have been studied by means of scanning tunneling microscopy (STM) and by highly sensitive laserionization spectroscopy of desorbed neutrals upon surface photoexcitation. On all of these surfaces, intrinsic sites of the surfaces are subject of bond rapture upon excitation, showing the intrinsic structural instability under valence excitation. The mechanism of the instability has been identified to be the two-hole localization; a dense population of valence holes forms a two-hole localized sate on intrinsic sites on surfaces to induce bond breaking and desorption. This finding enables us to generate new photoinduced phases of surface, typically shown for (1x1) structure of Si(001)-(2x1) generated by selective layer removal under laser excitation.These results have provided us crucial knowledge for establishing thorough understanding of the photoinduced processes on semiconductor surfaces.

该项目的目的是通过飞秒双光子光电子（2ppe）光谱来阐明半导体表面（一种典型的准二维系统）激发态的动力学。动力学知识提供了从微观角度理解表面光致结构变化机制的基础。主要结果总结如下：1)Si(001)-(2x1)上2ppe的飞秒分辨研究解决了表面态动力学的基本过程，包括体态到表面态的转变和表面态的减少。最重要的发现之一是从体态到表面态的转变速率取决于载流子密度。该速率与密度的平方成正比。由此,首次揭示了电子-电子散射在跃迁过程中的重要作用。2)通过扫描隧道显微镜(STM)和高通量研究了Si(111)-(7x7)、Si(001)-(2x1)、Si(111)-(2x1)和InP(110)-(1x1)表面的光致结构变化。表面光激发解吸中性粒子的敏感激光电离光谱。在所有这些表面上，表面的固有位点在激发时都会发生键断裂，显示出价激发下的固有结构不稳定性。不稳定性的机制已被确定为两孔局域化；密集的价空穴群在表面的本征位点上形成双孔局部状态，从而诱导键断裂和解吸。这一发现使我们能够生成新的表面光致相，通常显示为在激光激发下通过选择性层去除生成的 Si(001)-(2x1) 的 (1x1) 结构。这些结果为我们全面了解半导体表面的光致过程提供了重要的知识。