中文摘要
一般在矽晶圓上製作光振幅調變器，大多是在SOI的晶圓上製作出Mach-Zehnder結構的光強度調變器。但是SOI晶圓十分昂貴，且Mach-Zehnder的結構龐大複雜，製成要求的精確度高。因此本論文的目的就是為了要做出低成本、反應速度快、高光調變率並且可以符合現今CMOS製成的光強度調變元件。而我是參考1992年Huang等人在矽基板上利用P+P-N+的結構作出的光強度調變器，希望能在不使用SOI晶圓的情況下，可以用較Mach-Zehnder簡單的結構，來製作光振幅調變器。
在用矽來製作的光調變器中，最有效的調變方式就是利用自由載子(電子和電洞)注入的效應，一般都會在矽晶圓上掺雜出P和N的區域，利用二極體的結構在順偏時所產生的大電流，來達成自由載子注入的目的。其中P和N區域的掺雜方式大多都是用離子佈植的方式，但是那所須的成本很高。所以我採用SOD擴散掺雜的方式，來達成P和N區域掺雜的目的。用交大奈米中心的展阻量測系統(SRP)所量測SOD參雜的結果，掺雜濃度最高有1019(ions/cm3)，深度約為1微米。以及製作成P+P-N+二極體來量測電壓電流(I-V)的特性，確實可以觀察到二極體順偏時有高電流，逆偏時幾乎沒有電流的整流特性。
之後用光學系統量測後發現，自由載子的注入確實可以改變所通過光的振幅，並因為自由載子注入的效應，在二極體順偏時所輸出的光強度最低，而在二極體逆篇時所輸出的光強度較高。由上述量測結果可以知道我們確實成功的製做出光振幅調變器，以及量到它在不同調變長度和不同電流密度時對光調變率的關係。而量測到的最佳調變強度為在光波導寬度為30μm，調變距離為7mm，電流密度為6mA/mm時，由目前的量測系統所得到最大的光振幅調變率為1.1%。

Abstract
Until now, the silicon-based Mach-Zehnder (M-Z) optical modulators were mostly fabricated on the silicon-on-insulator (SOI) substrate. However, the cost of fabricating M-Z modulators is still considered relatively high due to the expensive nature of SOI wafers. Therefore, the ultimate purpose of this thesis is to fabricate a cost-effective optical amplitude modulator with high response speed, high modulation index, and most of all, still remains compatible to the current CMOS process. Our proposed technique of fabricating P+-P--N+ based optical amplitude modulator on silicon wafer is somewhat similar to the original work of Huang et al. when their result was first reported in 1992. Our whole intention is to fabricate amplitude-modulating devices which are simpler to the M-Z structure and at the same time to neglect the need of using the SOI wafer.
The most effective means to modulate silicon optical modulator is to rely on the carrier injection, or plasma dispersion effect. The technique is based on the p-i-n diode structure; while during the forward bias condition the carriers can be subsequently injected into the intrinsic region to serve the purpose of index modulation. Conventionally, the p- and n-doped regions were achieved via ion implantation method. However, the technique is time consuming and highly expansive. Hence, we introduce a much simpler technique using the spin-on-dopant (SOD) diffusion method to carry out the respective doping in both p and n regions. We then employ the spreading resistance probe system (SRP) housed in the Nano Facility Center of the National Chiao Tung University to verify the doping concentration and diffusion depth. The results later demonstrate that the highest doping concentration achieved is 1019/cm3 and the deepest diffusion depth is 1μm. Next, the I-V measurement is conducted to verify the diode nature of P+-P--N+ SOD-diffused structure. The result shows that the rectification is achieved at forward bias condition and very little or no current is observed at reverse bias condition.
The optical characterization is then carried out to verify the free carrier injection effect is in fact modulating the amplitude of light once the light passes through the device. The modulating nature based on the carrier injection effect is successfully observed when the intensity of output light becomes lowest as the diode is forward biased, while the opposite is true when the device is reversely biased.
Based on the aforementioned optical measurements we hereby conclude that the optical amplitude modulator is successfully fabricated and the influences of different modulation length and current density on the optical modulation index are also quantified. For the 30μm-wide waveguide modulator with the modulation length of 7 mm and the current density of 6mA/mm, the largest optical modulation index achieved is 1.1% using our device characterization system.

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