Study of photo-induced atomic processes on semiconductor surfaces by means of femtosecond spectroscopy

这个项目的目的是弄清楚清洁半导体表面上激光诱导电子不稳定性的微观过程。用飞秒激光脉冲和纳秒激光脉冲对超高Y腔体中的Si(111)-(7x7)和InP(110)-(1x1)表面进行了动力学研究和光谱激发。通过扫描隧道显微镜(STM)对原子结构的直接成像和解吸中性物种的高灵敏检测来研究诱导的结构变化。1)在重构半导体表面的典型例子--Si(111)-(7x7)表面上，激光诱导的电子不稳定性是由2.0 eV的表面特定电子跃迁引起的，然后由非线性局域化引起表面原子的键断裂。2)在InP(110)-(1x1)晶面上的不稳定性表现为准一角…更多的原子和电子性质，类似的激光诱导的电子不稳定性，但在结构变化上具有强烈的波长依赖性的形貌。在激发表面特定相变时，沿[110]方向产生P空位串，而在体电子激发下形成二维空位岛。这些特性可以归因于光生激发态在表面态和体电子态的不同性质，前者表现为一维性质，而后者在迁移率上是各向同性的。3)为了研究表面结构变化引起的脱附，我们成功地建立了一种高灵敏度的飞秒非共振电离光谱(FNRIS)同时检测多个中性物种的新方法。这种方法被应用于InP表面，表明脱附过程也是关于激发强度的强超线性的，类似于表面形成空位的情况。此外，对于清洁的(1x1)表面，脱附的主要产物为单原子P和原子，这与STM观察结果一致。我们在这个项目中获得的结果是第一次证明FNRIS是研究化合物半导体表面脱附的有力工具。较少

The purpose of this project is to make clear the microscopic processes of laser-induced electronic instability on clean semiconductor surfaces. The surfaces of Si(111)-(7x7) and InP(110)-(1x1) in an UHY chamber were excited either by fs-laser pulses for dynamical study or by ns- laser pulses for spectroscopy. Structural changes induced were studied by direct imaging of the atomic structures by scanning tunneling microscope (STM) and by high-sensitive detection of desorbed neutral species. Main results obtained in this project are summarized below.1) On Si(111)-(7x7), which is a proto-typical example of reconstructed semiconductor surfaces, laser-induced electronic instability is induced by the surface-specific electronic transition at 2.0 eV, followed by non-linear localization to induce bond breaking of adatoms on the surface. Two-hole localization followed by the phonon-kick process has been proposed to be the origin of the instability.2) On InP(110)-(1x1), which shows quasi-one dime … More nsional atomic and electronic properties, similar laser-induced electronic instability is induced, but with strongly wavelength-dependent morphologies in structural changes. Upon exciting surface specific transitions, P-vacancy strings are generated along [110] direction, while two-dimensional vacancy islands are developed upon bulk-electronic excitation. These characteristics can be ascribed to different properties of photo-generated excited species in surface states and in bulk electronic states ; the former shows one-dimensional nature, while the latter is isotropic in mobility.3) For studying desorption induced as a result of surface-structural changes, we successfully developed a new method of femtosecond non-resonant ionization spectroscopy (FNRIS) for detecting several neutral species simultaneously with high sensitivity. This method was applied for InP surfaces to show that desorption processes are also strongly super-linear with respect to the excitation intensity, similarly to the case of vacancy formation on the surface. Also, primary product of desorption has been confirmed to be monoatomic P and In atoms for clean (1x1) surface, being consistent with STM observation. Our results obtained in this project is the first demonstration of FNRIS to be a powerful tool for studying desorption from compound semiconductor surfaces. Less