Evaluation of local electric fields on the reconstructed surfaces of semiconductor

利用二次谐波产生技术计算了清洁半导体表面上的局部电场。强脉冲激光载流子激发引起的能带弯曲的变化表现为三阶非线性光学极化率引起的倍频强度的变化，这种变化与电场有关。然而，我们发现，样品温度的升高也可以通过我们工作中阐明的随温度变化的倍频效应来促进倍频强度的变化。在另一种评估表面局部电场的尝试中，研究了低温等离子体增强化学气相沉积多晶薄膜中纳米硅产生倍频的倍频效应。由于晶体尺寸的减小，倍频信号的增加可以用局部电场的增加来解释。我们还研究了室温下吸附银的倍频效应以及高温下在Si(111)-7x7上形成Si(111)-[平方根]3x[平方根]：3-Ag表面的倍频效应。研究发现，倍频效应的强度依赖于二维吸附原子气体(2DAG)在Si(111)-[平方根]3x[平方根]3-Ag表面上的密度随温度和银通量的变化。在室温下，银覆盖的倍频效应可以用表面等离子体共振来解释，而在高温下的倍频效应则表现为在Si(111)-[平方根]3x[平方根]：3-Ag附近形成的3D岛的作用。我们的倍频探测方法也证明了Si(111)-7x7表面上的局域电子自旋。

Local electric fields on the clean semiconductor surface is evaluated by means of second-harmonic generation technique. The changes in the band-bending induced by carrier excitation by an intense pulsed laser has manifested as a change in the generated SHG intensity througil the third order nonlinear optical susceptibility which is electric-field dependent. However, it is found that the sample temperature increase can also contribute to the change in the SHG intensity through the temperature dependent SHG clarified in our work. Thus, the observed dependence of the SH intensity on the pump fluence was analysed by taking into accont the both effects.In another attempt to evaluate the surface local electric field, the seeond-harmonic generation SHG from silicon nanocrystallites in polycrystalline films prepared by low-temperature plasma-enhanced chemical-vapor deposition has been studied. An increase in the SHG signal by decrease in the sizes of crystallites is, interpreted by the increased local electric filed. We also studied SHG during the adsorption of silver at room temperature as well as the formation of the Si(111)-【square root】3x【square root】 : 3-Ag surface at elevated temperatures on Si(111)-7x7.The SHG intensity is found to depend on the density of the two-dimensional adatom gas (2DAG) on the Si(111)-【square root】3x【square root】3-Ag surface as a function of temperature and silver flux. The increase of SHG with silver coverage at room temperature is interpreted by a surface plasmon resonance, while that at elevated temperatures show the role of 3D islands formed beside the Si(111)-【square root】3x【square root】 : 3-Ag.Local electron spins on the Si(111)-7x7 surface are also evidenced by our SHG detection method.