半導體載子傳輸結構應用於單晶片三維全光訊號傳輸之研究

Abstract

利用互補式金屬氧化物半導體技術所製作的光子元件已由波導結構、微共振腔以及兩者結合所廣泛應用實現，這些元件可以用於二維積體光路系統中。由於訊號傳輸、運算之技術快速發展並推動摩爾定律的前進，三維積體光路封裝技術以及單石三維積體光路技術也已經被研究開發，然而目前為止的技術類型，仍受限於元件尺寸不易微縮及三維整合彈性低等問題。在本論文中，為了實現一個全新型態的單石三維積體光子元件，我們先利用模擬及實驗之掃描式光電流顯微術，研究二、三維載子傳輸結構之載子傳輸行為。另一方面，我們亦開發了一個新的掃描式光致發光術之方法，來擷取薄膜元件之雙極性載子擴散長度。接著我們展示了一個全新型態的單石積體光子元件，稱之為光子層間孔元件 (photonic ILVs)，其利用半導體載子傳輸結構實現了三維全光開關切換，用於層間訊號的傳輸。 關於載子傳輸的研究，原先我們認為理想的一維掃描式光電流曲線會隨著二維傳輸結構之寬度變大而漸漸有所變異，然而我們模擬的結果顯示不同寬度的結構，其歸一化後的光電流曲線幾乎一致，為了釐清此現象，我們亦模擬了載子分布的情形，並發現載子經過有限寬度方向積分後沿通道方向之分布呈現一個簡單指數遞減函數形式，且其遞減常數即為理論計算之載子衰減長度，如同理想一維傳輸結構的載子分布特性。我們也確認了一維解析模型的光電流擬合公式在歐姆接觸之二維傳輸結構的適用性。另一方面，我們亦用模擬確認了簡單指數遞減函數可以用於擬合蕭特基接觸之二維傳輸結構的掃描式光電流曲線，並擷取出載子擴散長度。此外，我們更進一步地展示歐姆及蕭特基接觸之三維傳輸結構，在其電極完全包覆元件通道之寬度、厚度方向之邊界時，其掃描式光電流曲線將可退化為其對應之理想的一維函數形式。最終我們製作了P型砷化銦鎵空橋式兩端點元件並量測其掃描式光電流曲線。我們亦利用模擬的方式觀察並驗證表面複合速率對元件以及掃描式光電流曲線的影響，同時製作、量測不同寬度的絕緣層上覆矽兩端點元件來進行模型驗證，並利用與該元件寬度關聯的載子衰減長度來擷取出其表面複合速率值。 最終，我們展示了一個全新型態的單石積體光子元件-光子層間孔元件 (photonic ILVs)，其利用半導體載子傳輸結構實現了三維全光開關切換，用於層間訊號的傳輸。此元件包含一個垂直的矽微米柱，其一端嵌於上層氮化矽波導內用作光吸收，另一端則是嵌於下層氮化矽微碟共振腔用作折射率調製。我們先利用連續波雷射正面激發矽微米柱並觀察元件共振頻譜偏移量來研究矽微米柱之雙極性光生載子傳輸特性。基於光生載子可以傳輸於矽微米柱連通之不同層之間的特性，我們使用激發-探測技術且透過單晶片氮化矽波導、矽微米柱及氮化矽微碟共振腔，來實現完全積體化之全光學三維訊號開關切換。我們亦實驗觀察該光子層間孔元件受到離子轟擊後增加表面複合速率之影響。此元件展現了在單石三維積體光路系統中更實際且彈性的整合能力，具有應用於未來高速全光訊號運算及通訊之潛力。

Photonic devices using complementary-metal-oxide-semiconductor (CMOS) technology have been widely demonstrated using waveguides, micro-cavities, and the integration of both waveguides and micro-cavities, which can be applied in the two-dimensional photonic integrated circuits (2D-PICs). Due to the rapid development for the continuing trend of exponential growth with Moore’s law in data communications and processing, 3D-PICs packaging and monolithic 3D-PICs have also been studied and demonstrated in addition to their two-dimensional counterparts. However, these up-to-date techniques suffer from the large footprint or limited degree of integration. In this dissertation, to realize a brand new type of monolithic 3D photonic devices, we first studied the carrier transport both numerically and experimentally using scanning photocurrent microscopy (SPCM) in 2D/3D carrier transport structures. Then, we proposed and demonstrated a brand new type of monolithic photonic devices called photonic inter-layer vias (photonic ILVs), which realizes the 3D all-optical switching for inter-layer signal transmission by a semiconductor-based carrier transport structure. Regarding the study of carrier transport, originally, one would expect that with increasing width in 2D transport structures, scanning photocurrent profiles will gradually deviate from those of the ideal 1D transport structure. However, the scanning photocurrent simulation results surprisingly showed almost identical profiles from structures with different widths. In order to clarify this phenomenon, we observed the spatial distribution of carriers. The simulation results indicate that the integrated carrier distribution in the 2D transport structures with finite width can be well described by a simple-exponential-decay function with the carrier decay length as the fitting parameter, just like in the 1D case. For ohmic-contact 2D transport structures, the feasibility of the fitting formula from our previous 1D analytical model was confirmed. On the other hand, the application of a simple-exponential-decay function in scanning photocurrent profiles for the diffusion length extraction in Schottky-contact 2D transport structures was also justified numerically. Furthermore, our simulation results demonstrate that the scanning photocurrent profiles in the ohmic- or Schottky-contact three-dimensional (3D) transport structures with electrodes covering the whole terminal on both sides will reduce to those described by the corresponding 1D fitting formulae. Finally, experimental SPCM on a p-type InGaAs air-bridge two-terminal thin-film device was carried out. To observe the effect of device surface recombination velocity (SRV) in SPCM model, we also studied both numerically and experimentally. The silicon-on-insulator two-terminal device with varying widths was measured for model verification, and its SRV could be extracted from the width-dependent carrier decay length. Finally, we proposed and demonstrated a brand new type of monolithic photonic devices- photonic ILV which realizes the three-dimensional (3D) all-optical switching for inter-layer signal transmission. This device is composed of a vertical Si microrod which serves as optical absorption material within a SiN waveguide in one layer and as an index modulation structure within a SiN microdisk resonator lying in the other layer. The ambipolar photo-carrier transport property in the Si microrod was studied by measuring the resonant wavelength shifts under continuous-wave laser pumping directly on the top of a Si microrod. Based on the ambipolar photo-carrier transport in a Si microrod through different layers, we presented a fully-integrated all-optical switching operation using this Si microrod and a SiN microdisk with a pump-probe technique through the on-chip SiN waveguides. The photonic ILV device with the effect of increased surface recombination velocity through ion-bombardment was also observed. This device shows potential applications for the future high-speed all-optical computing and communication with more practical and flexible configurations in monolithic 3D-PICs.