Photo-Induced Structural Changes on Semiconductor Surfaces

用扫描隧道显微镜（STM）和高灵敏度的共振和非共振电离光谱测量研究了Si（111）-（7 x7）和InP（110）表面辐照引起的结构变化和组分原子的脱附。对于Si（111）-（7 × 7）表面，低强度激光脉冲激发通过电子键断裂，伴随着电子基态Si原子的脱附，选择性地在表面吸附原子位上产生空位。对激光诱导空位空间分布的统计研究表明，激光诱导空位的破键效率与空位位置有很强的依赖性。随着激发激光脉冲剂量的增加，效率保持恒定，这意味着位置依赖性不是由于任何累积效应，而是在单个激光脉冲内诱导的键断裂的特征。本研究还表明，电子键-br ...更多信息 实验结果表明，激发光的能量和能量密度对脱附效率有很大的影响，脱附Si原子的平动能量分布与激发光的波长、能量密度和持续时间无关。实验结果表明，Si（111）-（7 x7）表面电子激发的非线性局域化对Si（111）-（7 x7）表面的光致键断裂起着重要的作用.基于对实验结果的详细分析，我们提出了一种脱附机制，即在InP（110）-（1xl）表面电子带间的激发导致了一种具有强烈位阻效应的电子键断裂：激光辐照选择性地在P亚晶格产生空位。此外，还表明，随着激发剂量的增加，有效地形成了沿沿着In-P链选择性伸长的空位串，这意味着在邻近空位的原子位置处优先键断裂。在低剂量范围内，不同尺寸的空位串的总数密度线性增加，然后在单层的百分之几处饱和。由于激光诱导的完整晶格位数变化不大，空位数密度的饱和强烈地暗示了键断裂效率的降低。在理想晶格位置的电子断键效率随剂量的增加呈非线性增加，表明电子断键过程中包含非线性过程。基于对非线性效率的分析，我们认为双空穴局域化是电子键断裂的主要步骤。实验上观察到的效率饱和现象可以解释为光生表面自由空穴沿In-P链准一维沿着延伸的有效转移和俘获.本研究表明，半导体表面的表面电子激发态具有强的位置选择效率，并非线性局域化，导致局域原子键断裂.在两个表面上观察到的几何特征和结构变化效率的差异可能表明，电子键断裂强烈依赖于表面的结构和电子性质。少

Structural changes and desorption of constituent atoms induced by irradiations of Si (111) - (7x7) and InP (l10) surfaces have been studied by means of scanning tunneling microscopy (STM) and high-sensitivity measurements of desorbed species using resonant- and non-resonant ionization spectroscopy. For Si (111) - (7x7) surfaces, it has been shown that excitation with laser pulses with low intensity induces vacancies selectively at surface adatom-sites, via electronic bond-breaking, accompanied with desorption of Si atoms of electronic ground state. Statistical investigation of spatial distribution of the laser-induced vacancies have revealed strong site-dependence of the bond-breaking efficiency. The efficiency stays constant with increasing the dose of excitation laser pulses, meaning that the site-dependence is not due to any accumulative effects but a characteristic feature of bond-breaking induced within a single laser pulse. The present study also shows that the electronic bond-br … More eaking exhibits strong photon-energy and fluence dependent efficiency, and that the translational energy distribution of desorbed Si atoms independent of wavelength, fluence and time duration of excitation laser lights. Experimental results obtained in the present study have shown that non-linear localization of surface electronic excitations selectively at surface adatom sites plays an important role on the photo-induced bond-breaking on the Si (111) - (7x7) surface. Based on the detail analyses of the results, we have proposed a desorption mechanism including two-hole localization on a surface atomic site followed by bond-breaking via phonon-kick process.Similarly, excitation between surface electronic bands on InP (110) - (lxl) induces an electronic bond-breaking with a strong site-dependent efficiency : laser irradiation produces vacancies selectively at P sub-lattice. In addition, it has been also shown that vacancy-strings elongated selectively along In-P chains are formed efficiently with increasing excitation dose, meaning preferential bond-breaking at atomic sites neighboring to vacancies. The total number density of vacancy string with respective sizes increases linearly for low dose range, and then saturates at a few percent of monolayer. Since the laser-induced change of the number of perfect lattice sites is little, the saturation of number density of vacancies suggests strongly the decrease of bond-breaking efficiency. The efficiency of electronic bond-breaking at perfect lattice sites shows non-linear increase with increasing dose, suggesting that non-linear process are included in the bond-breaking. Based on analyses of the non-linear efficiency, we suggest that two-hole localization is included as a primary step of the electronic bond-breaking. Experimentally observed saturation of the efficiency may be explained by efficient transfer and trapping of photo-generated surface free holes, which are extended quasi-one dimensionally along the In-P chain.The present study have demonstrated that the surface electronic excited states on semiconductor surfaces are localized non-linearly with a strong site-selective efficiency, leading to breaking of local atomic bonds. Observed difference in geometric feature and efficiency of structural changes on the two surfaces may indicate that the electronic bond breaking depends strongly on structural and electronic properties of the surfaces. Less