運用於光纖通訊、光連接網路及光碟機讀寫頭等各式應用的氧化侷限垂直共振腔面射型雷射目前已成為一重要之半導體雷射光源。藉由選擇性氧化埋入鄰近主動層之高Al含量AlGaAs磊晶層，可以控制電流的流動方向並產生光場的侷限作用，進而得到低臨界電流及高效率的雷射。製程上為了暴露出高Al含量的AlGaAs磊晶層，因此必須以乾或濕蝕刻方式蝕刻出幾個微米(∼μm)深之溝槽，然而此一高深寬比之台柱型結構會造成元件在積體化運用的困難，同時也會妨礙元件所生熱之橫向散逸。因此如何改善氧化侷限垂直共振腔面射型雷射的製程，以提高元件的效能及符合積體化製程要求，是目前非常重要且刻不容緩的研究課題。
本論文率先提出氧化矽平坦化技術，並將其施行於發光波長為850-nm之氧化侷限垂直共振腔面射型雷射上，以改善傳統光阻塗佈聚醯亞胺(polyimide)平坦化技術中材料本身所隱含的缺點。對於氧化孔徑為6 μm的850-nm面射型雷射其臨界電流(Ith)為0.88 mA對應的操作電壓(Vth)為2.05 V；當元件操作在60℃下，具有一最低的臨界電流0.7 mA；此外，雷射的外部量子效率為43%，並可操作在溫度大於130℃的環境；當注入電流增加時，元件會激發出高階橫模態(transverse mode)，其中最低階的橫模(波長最長)隨電流紅移速率為0.49 nm/mA。另一方面，經由熱阻的計算，相較於未填埋入氧化矽的相同尺寸元件，氧化矽平坦化元件具有一較低的熱阻並表現出較佳的特性。最後，這個元件操作於3.7 mA下，具有最大的位元傳遞速率8 Gb/s。
為改善元件特性並壓抑高階橫模態的產生，經由縮小氧化孔徑至小於4 μm與利用氧化矽平坦化技術，可得到一單橫模(single transverse mode)且高效率的850-nm氧化侷限垂直共振腔面射型雷射。對於氧化孔徑為3 μm的850-nm面射型雷射其臨界電流為0.52 mA對應的操作電壓為2.2 V；雷射的外部量子效率為35%。同時在操作電流範圍內，元件均可保持單一橫模發光頻譜。另一方面，封裝於TO-46 head上的元件可操作在位元傳遞速率為10 Gb/s，即使光訊號通過66 m多模光纖傳輸，接收端所測得的眼圖仍能呈現一高對稱性且張開度大的影像。此外，系統誤碼率(BER)的量測結果顯示，在誤碼率10-11下(近似無誤碼狀況)，由於光纖本身的色散現象(fiber dispersion)使光訊號通過66 m多模光纖傳輸後，會造成6.6 dB的額外功率償付(power penalty)。這些結果確認氧化矽平坦化之850-nm氧化侷限垂直共振腔面射型雷射具有優異的動態特性。
由於長程光纖通信在1.3 μm與1.55 μm有兩個光訊號的低損失窗，因此，經由引入GaInNAs主動層結構與利用氧化矽平坦化技術，我們成功地開發出高效率的1.3-μm氧化侷限垂直共振腔面射型雷射。對於氧化孔徑為12 μm的1.3-μm面射型雷射其臨界電流為3.5 mA對應的操作電壓為2 V。此外，就目前所知，在相似的磊晶結構下，元件具有最大輸出光功率1.86 mW和光輸出效率(slop efficiency) 0.22 W/A並可操作在溫度大於80℃的環境；當注入電流增加時，元件最低階的橫模隨電流紅移速率為0.45 nm/mA，在注入電流12 mA下發光波長為1284.4 nm。最後，這個元件操作在位元傳遞速率2.5 Gb/s和12 mA下，所測得的眼圖呈現一高對稱性且張開度大的影像。這些結果確認氧化矽平坦化之1.3-μm氧化侷限垂直共振腔面射型雷射具有運用於長距離光纖傳輸的潛力。

Selectively oxidized vertical-cavity surface-emitting laser (VCSEL) now is regarding as a very important light source for many optoelectronic applications, such as high-speed LANs, computer links, and optical interconnects, etc. However, due to the device with intentional mesa geometry, which causes an obstacle for its versatile applications. In this dissertation, a state of the art processing technique is presented to fabricate a planar-type oxide-confined 850-nm VCSEL. The planarized process of VCSELs was to use the silicon oxide (SiOx) as the buried layer. As a result, these devices exhibit excellent static characteristics, including a threshold voltage (Vth) of 2.05 V corresponding to a threshold current of 0.88 mA, a minimum threshold current of 0.7 mA near 60℃, a maximum output power of 4.28 mW at 11 mA, a maximum external differential quantum efficiency (ηex) of 43 % just above threshold, and an operation temperature beyond 130℃. In addition, the transverse modes of the device initially are low-order, while high-order modes appear at elevated current levels. The fundamental transverse mode at the longest wavelength increases with injected current with a red shift of 0.49 nm/mA due to joule effect. Since the thermal resistance of the VCSEL with a SiOx buried layer is less than that of device without it, the VCSEL with a SiOx buried layer displays less red shift and better performance. Finally, the VCSEL with a SiOx buried layer shows a clear eye-opening feature as operating at 2.488 Gbit/s with a bias current of 2 mA. Further increasing the current level, the device can work at the maximum bit rate of 8 Gbit/s and a bias current of 3.7 mA.
Because of the strong optical confinement and the larger transverse dimension, VCSELs made with oxide apertures tend to lase in high-order Laguerre-Gaussian modes at elevated current levels. This in turn leads to a problem in fiber coupling because the beam divergence from these high-order modes is much higher than the fundamental mode. In addition to poor overall fiber coupling efficiency, the quality of the optical signal is also influenced by the amount of light coupled, and how each of the individual modes is sampled. The mode dynamics in the device can cause another problem, i.e., mode partition noise, which will further deteriorate the optical signal under system data transmission. With reduction the size of the oxide aperture to the point where only the fundamental mode is supported, we have succeeded in fabricating a high-efficiency SiOx-planarized single-transverse emission 850-nm VCSEL. These devices with an oxidized aperture of 3 μm in diameter exhibit a single-transverse mode behavior throughout the operation current range. In addition, the static characteristics of VCSELs at 300K include a threshold current of 0.52 mA corresponding to a threshold voltage of 2.2 V, a maximum single transverse-mode light output power of 1.13 mW at 4.5 mA, and an external differential quantum efficiency of 35%. On the other hand, this TO-packaged planar-type 850-nm VCSEL for back-to-back test shows a wide open along with symmetric eye diagram and could also pass the 10 Gb/s mask as operating at 10.3 Gb/s and 4 mA. Furthermore, the VCSEL can still keep the eye diagram open and symmetric after the 66-m multi-mode fiber (MMF) transmission and has a power penalty of 6.6 dB because of fiber dispersion for 10.3 Gb/s data rate at a bit error rate of 10-11. These results confirm the excellent high-speed performance of SiOx-planarized VCSELs as compared to the polyimide-planarized VCSELs.
On the other hand, for improved transmission distance over MMF and for extended reach over single-mode fiber, it is desirable to operation around 1.3-μm. Based upon the SiOx-planarized technique, we report on a novel high-efficiency planar-type oxide-confined 1.3-μm GaInNAs VCSEL. The devices exhibit excellent static characteristics at room temperature, including a threshold voltage of 2 V corresponding to a threshold current of 3.5 mA, a maximum light output power of 1.86 mW measured at 15 mA. To our knowledge this output power is the best when compared to those obtained with conventional VCSEL processes for the similar epitaxial structure design. The VCSELs show a threshold current density of 3100 A/cm2, a differential resistance at half of maximum power of 110 Ω, a slope efficiency of 0.22 W/A above the threshold, and a continuous wave operation temperature up to 80℃. In addition, when operating at 4 mA these devices exhibit a single-mode emission with the transverse-mode suppression of more than 20 dB and an output power of 0.12 mW. The wavelength of the strongest emission peak, which corresponds to the fundamental transverse mode, increases with injection current at a red shift of 0.45 nm/mA from 1280.6 nm at 4 mA to 1284.4 nm at 12 mA due to a joule effect. Finally, this planar-type 1.3-μm VCSEL shows a clear and symmetric eye diagram operating at 2.488 Gb/s at 12 mA. These results confirm the SiOx-planarized GaInNAs VCSELs have the potential capacity for fiber optic applications.

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