成長於鍺基板高速940 nm垂直共振腔面射型雷射之研究

Abstract

因應當今自動化光感測、光通訊高速互聯與虛擬實境等次世代光電半導體科技的蓬勃發展，使得身為各系統中關鍵光源零組件的氧化物限制-垂直共振腔面射型雷射（VCSELs）市場需求與日俱增。近年來，基於鍺基板之VCSELs元件因材料散熱特性優異，且可以銜接大尺吋晶圓製造等因素，逐漸被視為具經濟效益與高溫穩定性元件生產的新途徑。本文主要在分析基於鍺基板VCSELs元件直流、高頻訊號調制、元件物理模型與大訊號調制之相關特性，並與成長於砷化鎵基板之元件進行比較，以確認鍺基板元件製造的可行性與元件表現。 第一章主要將針對氧化物限制-垂直共振腔面射型雷射進行元件介紹，並提出有關於本研究之研究動機，以及鍺基板元件之研究背景需求。 第二章將會針對近幾年研究鍺基板VCSELs之相關文獻進行介紹，並運用與加拿大UBC大學合作之鍺基板磊晶進行標準化製程，再透過量測元件的直流特性以分析鍺基板在環境溫度變化下與砷化鎵基板元件之差異，從結果中得知鍺基板元件在氧化孔徑6 um時，於1.6 mA有0.54 W/A之良好的斜率效率，因而在高頻訊號調制時可以提供更快的光學響應與轉換線性度並減少資料傳輸的失真，後續熱阻的分析由於鍺基板良好的熱導率，具有極小的熱阻值使其半導體接面溫度隨電流上升較砷化鎵基板元件緩慢，在10 mA操作下兩種基板元件接面溫差約42 K。 第三章將運用網路分析儀對元件進行高頻響應的量測，以探討鍺基板元件是否能滿足當今光通訊系統所需光源之操作頻寬，從量測結果得知鍺基板於光孔徑3 um具有最快之調製頻寬為19.85 GHz，另外由於鍺基板優異的散熱性能與低缺陷密度，使其元件的響應頻寬隨環境溫度上升而下降的情況較砷化鎵基板元件緩慢，也間接證明鍺基板元件在高溫操作下具有較好的穩定性與可靠度。 第四章則利用了先前量測元件高頻響應的結果，搭配VCSELs元件的物理模型進行擬合，以萃取鍺基板與砷化鎵基板元件的小訊號模型，並分析兩種基板元件的本質響應與外部寄生效應的影響情況，發現鍺基板的接面電阻相較於砷化鎵基板較小且隨溫度變化較不劇烈。後續也透過量測大訊號調制之眼圖分析兩種基板元件的高速傳輸速率能力，而鍺基板元件最高可達到80 Gbps的高速傳輸速率，基於各樣元件特性分析，皆表明鍺基板極有潛力可成為VCSELs製造的全新方針。

In response to the rapid development of next-generation optoelectronic semiconductor technologies such as automated optical sensing, high-speed optical communication, and virtual reality, the market demand for oxide-confined vertical cavity surface emitting lasers (VCSELs), which are critical optical source components in various systems, has been increasing daily. In recent years, VCSELs based on germanium (Ge) substrate have gradually been seen as a new approach for the cost-effective production of high-temperature stable devices due to their excellent thermal dissipation properties and the ability to integrate with large-size wafer manufacturing. This paper primarily analyzes the DC, high-frequency signal modulation, device small-signal model, and large-signal modulation characteristics of VCSELs based on Ge substrate, comparing them with devices grown on gallium arsenide (GaAs) substrate to confirm the feasibility and performance of Ge substrate device manufacturing. The first chapter introduces the VCSELs, presenting the research motivation for this study and the research background needs for Ge substrate devices. The second chapter introduces the relevant literature on Ge substrate VCSELs research in recent years, using the standardized process of Ge substrate epitaxy in cooperation with the University of British Columbia, Canada. The DC characteristics of the devices are measured to analyze the differences between Ge substrate and GaAs substrate devices under varying environmental temperatures. Results show that Ge substrate devices exhibit a good slope efficiency of 0.54 W/A at 1.6 mA with an oxide aperture of 6 μm, providing faster optical response and conversion linearity during high-frequency signal modulation, thus reducing data transmission distortion. Subsequent thermal resistance analysis indicates that due to the excellent thermal conductivity of Ge substrate, they have extremely low thermal resistance, causing the semiconductor junction temperature to rise more slowly than in GaAs substrate devices at 10 mA operation, with a junction temperature difference of about 42 K between the two types of substrate devices. The third chapter employs a network analyzer to measure the high-frequency response of the devices to explore whether Ge substrate devices can meet the operating bandwidth requirements of current optical communication systems. Measurement results show that Ge substrate with a light aperture of 3 μm have the fastest modulation bandwidth of 19.85 GHz. Additionally, due to the superior thermal performance and low defect density of Ge substrate, their response bandwidth decreases more slowly with increasing ambient temperature compared to GaAs substrate devices, directly demonstrating the better stability and reliability of Ge substrate devices under high-temperature operation. The fourth chapter uses the previously measured high-frequency response results of the devices, fitting them with the physical model of VCSELs to extract the small-signal models of Ge and GaAs substrate devices. The intrinsic response and the impact of external parasitic effects of the two types of substrate devices are analyzed, revealing that the junction resistance of Ge substrate is relatively lower than that of GaAs substrate and varies less with temperature changes. Subsequent eye diagram measurements of large-signal modulation analyze the high-speed transmission rate capabilities of the two types of substrate devices, with Ge substrate devices achieving a maximum high-speed transmission rate of up to 80 Gbps. Based on various device characteristic analyses, it is evident that Ge substrate have great potential to become a new direction for VCSELs manufacturing.