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

本项目的目的是弄清楚激光在清洁半导体表面上引起的电子不稳定性的微观过程。在UHY室中，Si（111）-（7 × 7）和InP（110）-（1 × 1）表面分别用fs激光脉冲激发用于动力学研究和ns激光脉冲激发用于光谱学研究。诱导的结构变化进行了研究，通过扫描隧道显微镜（STM）的原子结构的直接成像和高灵敏度检测解吸的中性物种。1）在Si（111）-（7 x7）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，随后是非线性局域化，导致表面上吸附原子的键断裂。在InP（110）-（1x 1）晶体中，由于声子反冲过程导致的双空穴局域化是不稳定性的根源 ...更多信息 的原子和电子的性质，类似的激光诱导的电子不稳定性的诱导，但强烈的波长依赖的形态结构的变化。在激发表面特定跃迁时，沿[110]方向产生沿着的P型空位串，而在体电子激发时则形成二维空位岛。这些特征可以归因于光生激发态在表面态和体电子态的不同性质;前者显示一维性质，而后者在迁移率上是各向同性的。3）为了研究由于表面结构变化而引起的解吸，我们成功地发展了一种新的飞秒非共振电离光谱（FNRIS）方法，用于以高灵敏度同时检测几种中性物质。这种方法被应用于磷化铟表面显示，解吸过程也强烈的超线性相对于激发强度，类似于在表面上的空位形成的情况。此外，解吸的主要产物已被证实是单原子的P和In原子的清洁（1 × 1）的表面，与STM观察一致。我们在这个项目中获得的结果是第一次演示FNRIS是一个强大的工具，用于研究从化合物半导体表面的脱附。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