Desorption Induced by Electronic %excitation on Solid Surfaces

在化合物半导体GaP的清洁（1^^-1^^-1^^-）表面上测量了激光辐照引起的脱附和相关的表面改性。LEED观察到的结构变化引起的间接带隙能量附近的激光脉冲的照射表明，结构变化引起的实验条件下的温度上升是不显着的。为了弄清楚导致结构变化的电子激发的性质，我们测量了阈值激光能量密度的波长依赖性，在该阈值激光能量密度之上，干净的（17 × 17）重建表面结构变为（1 × 1）结构。结果提出明确的证据表明，清洁表面的改性发生在间接带隙能量附近的表面电子激发。Ga原子的结构变化和脱附与激光能量密度的超线性关系表明，这种原子过程是由表面态的密集激发引起的。结果表明，Ga脱附的阈值激光能量密度与激光辐照引起结构变化的阈值激光能量密度相同。除了结构变化的测量结果之外，该结果没有给出关于解吸机理的信息。在脱附测量中检测到的少量Ga原子表明，结构变化可能主要是由P原子的脱附引起的。这可能表明，磷原子的脱附测量提供了更多的信息，由电子激发引起的脱附机制。

Desorption and associated surface modification induced by laser irradiation are measured on the clean (1^^-1^^-1^^-) surfce of the compound semiconductor GaP. LEED observations of the structure change induced by irradiation with laser pulses near indirect band gap energy show that structure change induced under an experimental condition where the temperature rise is not significant. To make clear the nature of the electronic excitation leading to structure change, we measured the wave length dependence in the threshold laser fluence above which the clean (17x17) reconstructer surface structure change to (1x1) structrue. The results present clear evidence that the modification of clean surfaces occurs by surface electronic excitation near indirect band gap energy. The strong super linear dependence of the structure change and desorption on the laser fluence suggests that such atomic processes are induced by dense excitation of surface state.The desorption of Ga atoms were measured by means of resonant ionization spectroscopy using tunable dye laser. It shows that the threshold laser fluence for Ga desorption is just the same as that for the structure change by laser irradiation. This result does not give information on the mechanism for the desorption in addition to that from the measurement of the structure change. The small number of Ga atoms detected in desorption measurement, howerer, shows the possibility that the structure change mainly induced by the desorption of P atoms. It may suggest that the measurement of desorption of P atoms give more information on the mechanism of the desorption induced by electronic excitation.