用於 50 Gbit/sec 被動式光纖網路的超高速 累增崩潰光電二極體之開發;The Development of Ultrafast Avalanche Photodiode for 50G PON

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Title:	用於 50 Gbit/sec 被動式光纖網路的超高速累增崩潰光電二極體之開發;The Development of Ultrafast Avalanche Photodiode for 50G PON
Authors:	吳燁昆;Wu, Yen-Kun
Contributors:	電機工程學系
Keywords:	被動式光纖網路;累增崩潰光電二極體
Date:	2024-07-25
Issue Date:	2024-10-09 17:11:21 (UTC+8)
Publisher:	國立中央大學
Abstract:	在過去的 20 年裡，高速雪崩光電二極體（APDs）在以太網被動式光纖網絡（EPON）和 10 G-EPON 的發展中扮演了至關重要的角色。商業化的基於 In0.52Al0.48As 的 10 G APDs 通常能夠提供比其 p-i-n 光電二極體（PDs）對應產品高出 8 dB 的靈敏度。然而，在下一代 50 G-PON 中，APDs 在中等增益操作（約 10）下所展示的 3-dB 帶寬不足以滿足 50 G 操作的頻寬要求（>30 GHz），這使得 50 G APD 接收器的靈敏度提升並不明顯。已有研究表明，可以通過使用複雜的均衡器積體電路（ICs）和高功率 PD 與半導體光放大器（SOA）進行混合或單晶積體化整合來改善接收端的靈敏度。然而，這些額外的 ICs 和預放大的SOAs需要大電流偏壓，導致接收端的總功率消耗顯著增加。此外，SOAs 中的額外放大自發輻射（ASE）雜訊可能導致接收端靈敏度的改善非常有限。在高速雪崩光電二極體（APD）中，減薄倍增（M）層是提高其增益帶寬積（GBP）和降低過量雜訊的有效方法。然而，這種縮減通常伴隨著一些問題，例如由於非常薄的累增層（<100 nm）導致的直接 v 隧道效應引起的巨大漏電流（>1 μA），以及由於空乏層厚度減少而導致的 RC 限制頻寬下降。在本篇論文中，我們展示了一種p極面朝上蝕刻平台結構的APD，其中在薄(<50nm)且疊接式的 In0.52Al0.48As 累增層下方埋有厚的 InP 集極層，可以從根本上降低暗電流、RC 限制頻寬、累增增益和雪崩延遲時間之間的權衡。應用這種先進的元件結構，我們探討了具有不同累增層厚度（<50 nm）的 APD 性能。而此元件的主動窗口(平台) 其直徑為 10（20）μm，其優化後的累增層元件在 1.55 μm 波長的激發下，於偏壓為 0.9Vb 時有著低暗電流(~0.4 μA)和高響應度（2.8 A/W；增益=9.3）的表現。此外，該元件表現出優異的動態性能，包括在 0.84 A/W 時的寬光電頻寬（44 GHz）、極大的 GBP（1.03 THz）和高飽和電流（12 mA），這對應於在 45 GHz 時較大的毫米波（MMW）輸出功率（~0 dBm）。我們的增益頻寬積表現甚至超越最近所發表的 Si-Ge APD。優異的速度性能結合寬動態範圍和簡單的頂部收光結構，為進一步提高 50 G 的被動式光纖網絡（PON）的靈敏度開闢了新可能。;Over the last 20 years, high-speed avalanche photodiodes (APDs) have played a vital role in the development of the Ethernet Passive Optical Network (EPON) and 10 G-EPON. The commercially available In0.52Al0.48As based 10 G APDs can usually provide an 8 dB higher sensitivity than that of their p-i-n photodiode (PDs) counterparts. However, in the next generation of 50 G-PON, the 3-dB bandwidth demonstrated by APDs under moderate gain operation (~10) is insufficient to meet the bandwidth requirements for 50 G operation (> 30 GHz), with less pronounced benefits for the sensitivity of 50 G APD based receivers . It has been demonstrated that the sensitivity at the receiver-end can be improved by the incorporation of complex equalizer integrated circuits (ICs) and high-power PDs, which are hybrid or monolithic integrated with the semiconductor optical amplifier (SOA). However, both the additional ICs and pre-amplified SOAs need large extra bias currents which leads to a significant increase of overall power consumption in the receiver-end. Moreover, the additional amplified spontaneous emission (ASE) noise in the SOAs may result in marginal improvement in sensitivity in the receiver-end. ii The thinning of the multiplication (M) layers in high-speed avalanche photodiodes (APDs) is an effective way to boost up its gain-bandwidth product (GBP) and reduce excess noise. However, such downscaling usually comes with a price, a huge leakage current (> 1 μA) induced by direct tunneling through the ultimate thin M-layer (< 100 nm) and degradation of the RC-limited bandwidth due to the decrease in depletion layer thickness. In this work, we demonstrate how a p-side up top-illuminated APD structure with a thick InP collector layer buried below the thin and cascaded In0.52Al0.48As based multiplication layer can fundamentally relax the tradeoffs among the dark current, RC-limited bandwidth, multiplication gain, and avalanche delay time. Applying this advanced device structure, we then explore the performance of APDs with different thin M-layer thicknesses (< 50 nm). Under1.55 μm wavelength excitation, a device fabricated with a large active window (mesa) diameter of 10 (20) μm and an optimized M-layer thickness exhibits a dark current as low as ~0.4 μA and a high responsivity (2.8 A/W; gain=9.3) at 0.9 Vbr. Moreover, this device exhibits excellent dynamic performance, including a wide optical-to-electrical bandwidth (44 GHz at 0.84 A/W), an extremely large GBP of 1.03 THz, and a high saturation current (12 mA), which corresponds to a large millimeter-wave (MMW) output power (~0 dBm) at 45 GHz. iii The excellent speed performance coupled with the wide dynamic range and simple top-illuminated structure opens up new possibilities to further enhance the sensitivity of 50 G passive optical networks (PONs).
Appears in Collections:	[Graduate Institute of Electrical Engineering] Electronic Thesis & Dissertation

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