Study of all optical switch using quantum dots structure

在量子点的研究中，首先研究了量子点的生长条件，包括先前的条件。为了制作均匀的量子点，我们使用了自尺寸限制（Self Size limit， SSL）现象，这种现象由于量子点表面的出现而有效地安排了量子点的尺寸。为了增强SSL的效果，我们在低生长速率和低V/III比的条件下生长量子点，并改善（631）面出现的量子点的均匀性。其次，研究了平面InP覆盖层的生长条件，降低生长速率和提高V/III比对InP覆盖层的表面平整度有效。我们改善了表面平整度，RMS值为0.4nm。然后，用PL光谱与常规量子点进行比较，研究了均匀量子点的光学性质。结果表明，在40meV时，由于SSL的存在，FWHM得到了很大的改善，但由于量子点体积的增加，峰值波长出现了红移。我们尝试制作具有InP间距层的2,3,5堆叠结构，以研究堆叠数和层下gaina与量子点的关系。首先，通过在层下插入gaina，阻止了In从层下迁移，从而抑制了量子点尺寸的增加。当叠加数增加时，量子点变大，密度变低，并发生蓝移，这可归因于应变效应。在全光开关的研究中，我们测量了选择性MOVPE生长波导的非线性吸收和折射率变化。在用Fabry-Perot法测量吸收损耗时，在有源区吸收系数大于90cm^<-1>，在无源区吸收系数小于40cm^<-1>。在非线性折射率变化的测量中，我们利用马赫-曾德干涉仪测量了0.025%的折射率变化，并成功地获得了马赫-曾德型光开关的所有光开关特性。

In the study of quantum dots (QDs), QDs growth condition which includes previous conditions were investigated at first. To make uniform QDs, we use the phenomenon called Self Size Limiting (SSL), which is effective to arrange QDs size due to appearance of facet on the QDs. To enhance the effect of SSL, we grew QDs at low growth rate and low V/III ratio then we improve uniformity of the QDs on which (631) facet appeared. Next, growth condition for flat surface InP capping layer were investigated Reduction of growth rate and increase of V/III ratio were effective for surface flatness of InP capping layer. We improve surface flatness with the RMS value of 0.4nm. After then, optical property of the uniform QDs were investigated by PL spectra compared with conventional QDs. As the results, great improvement of FWHM as 40meV due to SSL was observed However, red shift of peak wavelength due to increase volume of the QDs was observed. We attempted to fabricate 2, 3, 5 stacking structure with InP spacing layer to investigate the dependence of stacking number and GaInAs under layer to QDs. At first, by inserting GaInAs under layer, In migration from under layer were prevented resulted in suppression of increase of QDs size. When we increase stacking number, QDs became large and low density with blue shift according to PL spectra It would be attributed to strain effect. In the study of all optical switch, we measured the nonlinear absorption and refractive index change in the waveguide grown by selective MOVPE growth. In the measurement of absorption loss by using the Fabry-Perot method, the absorption coefficient was more than 90cm^<-1> in the active region and less than 40cm^<-1> in the passive region. In the measurement of nonlinear refractive index change, we measured 0.025% refractive index change by using Mach-Zehnder interferometer And we have successfully obtained the all optical switching characteristics in the Mach-Zehnder type optical switch.