Point Defects in Ge-doped SiO_2 Glass-Their Structures and Roles in Nonlinear Optical Effects

(1)在掺锗SiO_2玻璃中，通过Kramers-Kronig关系引起光折变的吸收变化的产生机理尚未明确。在本文中，我们研究了KrF准分子激光在5ev左右诱导的吸收变化与激光功率的关系。5 eV附近的诱导吸收由三个不同的分量组成，以4.50、5.08和5.80 eV为中心。每个吸收组分的增加行为在很大程度上取决于能量密度。根据能量密度的不同，这三种吸收成分达到不同的饱和水平。此外，高功率KrF准分子激光诱导的吸收被能量密度约为诱导激光的二十分之一的激光漂白。结合数学分析结果，发现每次吸收的诱导和漂白分别涉及双光子过程和单光子过程。更重要的是，引起吸收变化的前体缺陷属于缺氧型。(2)测量了KrF准分子激光辐照后，缺氧掺锗硅玻璃的光吸收随时间的微秒级变化。发现3ev以上的吸收与3.1 eV的发光衰减的时间常数相同。由此证实，所观察到的吸收变化是由于电子从最低的激发态激发到更高的态。(3)利用KrF （5.0 eV）准分子激光和同步辐射激发的光致发光（PL）表征了氧离子注入在Si中形成的SiO_2埋膜缺陷。在4.3和2.7 eV下观察到两个PL波段。4.3 eV波段有5.0和7.4 eV两个PL激发带，5.0 eV和7.4 eV的衰减时间分别为4.0 ns和2.4 ns。2.7 eV PL波段的衰减时间为9.7 ms。这些结果与4.3 eV和2.7 eV PL波段的结果非常相似，这是在缺氧型的大块硅玻璃中观察到的，归因于氧空位。通过PL强度随膜厚的变化，可以认为埋藏的SiO_2膜在整个氧化物中含有大量的氧空位缺陷。少

(1) The generation mechanism of the absorption changes, which cause a photorefractive change through the Kramers-Kronig relation in Ge-doped SiO_2 glass, has not been clarified yet. In the present paper, we examined the laser-power dependence of the absorption changes around 5 eV,induced by a KrF excimer laser. The induced absorption around 5 eV is composed of three different components, centering at 4.50,5.08, and 5.80 eV.The increasing behavior of each absorption component depends strongly on the energy density. The three absorption components reach different saturation levels, depending on the energy density. Furthermore the absorption induced by a high-power KrF excimer laser is bleached by a laser, the energy density of which is about one-twentieth of the inducing laser. Combining the results of mathematical analysis, it was found that a two-photon process and a one-photon process are, respectively, involved with the induction and the bleach of each absorption. It was also found t … More hat the precursor defects, which causes the absorption change, is of an oxygen-deficient type.(2) Optical absorption change in the microsecond order in oxygen-deficient Ge-doped silica glass was measured as a function of time just after photon irradiation from a KrF excimer laser. The absorption above 3 eV was found to decay with the same time constant as that of the luminescence at 3.1 eV.From this, it is confirmed that the observed absorption change is due to the excitation of electrons from the lowest excited triplet state to an upper state.(3) Defects in buried SiO_2 films in Si formed by implantation of oxygen ions were characterized by photoluminescence (PL) excited by KrF (5.0 eV) excimer laser and synchrotron radiation. Two PL bands were observed at 4.3 and 2.7 eV.The 4.3 eV band has two PL excitation bands at 5.0 and 7.4 eV,and its decay time is 4.0 ns for the 5.0 eV excitation and 2.4 ns for the 7.4 eV excitation. The decay time of the 2.7 eV PL band is found to be 9.7 ms. These results are very similar to those for the 4.3 eV and the 2.7 eV PL bands, which are observed in bulk silica glass of an oxygen-deficient type and attributed to the oxygen vacancy. Through the change in the PL intensity with the film thickness, the buried SiO_2 film is considered to contain the oxygen vacancy defects in a high amount throughout the oxide. Less