Evaluation of local electric fields on the reconstructed surfaces of semiconductor

利用二次谐波产生技术对清洁半导体表面的局部电场进行了评价。强脉冲激光激发载流子引起的带弯曲变化表现为产生的SHG强度的变化，其三阶非线性光磁化率与电场有关。然而，通过我们工作中阐明的温度依赖性SHG，我们发现样品温度的升高也会导致SHG强度的变化。因此，通过考虑这两种影响，分析了观测到的SH强度对泵流量的依赖关系。在另一个评估表面局部电场的尝试中，我们研究了低温等离子体增强化学气相沉积法制备的多晶薄膜中硅纳米晶的次谐波产生。晶体尺寸的减小导致SHG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时的SHG，以及Si(111)-7x7上高温下Si(111)-【平方根】3x【平方根】：3-Ag表面的形成。发现SHG强度取决于Si(111)-【平方根】3x【平方根】3-Ag表面上二维adatom气体（2DAG）的密度，是温度和银通量的函数。在室温下，表面等离子体共振解释了银覆盖下SHG的增加，而在高温下，SHG的增加表明Si(111)-【平方根】3x【平方根】：3-Ag旁边形成的三维岛的作用。我们的SHG检测方法也证实了Si(111)-7x7表面的局部电子自旋。

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.