| 摘要: | 由於AI互連對通道頻寬的需求不斷增長，對光電（O-E）與電光（E-O）元件或模組進行近 DC 至 300 GHz 的寬頻量測變得非常重要。與傳統毫米波技術在寬頻訊號產生與傳輸上的方法相比，採用光子方法可用單一超快光電二極體取代體積龐大且多顆倍增器、電纜與波導轉接頭等的解決方案，大幅降低量測困難，提高擴展性並保有高功率表現。在這樣的架構中，光電轉換頻寬與輸出功率對動態範圍的表現扮演關鍵角色。
本論文研究了不同接面結構下超快光電二極體（PD）的動態特性，這些結構分別為鋅擴散型與原生生長型 p-n 接面，以比較哪一種能提供較高的飽和功率表現。研究中所使用的光電二極體為基於 InP 的單載子傳輸光電二極體（UTC-PD），其吸收層為 type-II GaAs₀.₅Sb₀.₅（p）/In₀.₅₃Ga₀.₄₇As（i）混合結構。藉由這種吸收層設計，可因能隙變窄與 type-II 接面處光吸收增強的效果，提高元件的響應度。
儘管採用鋅擴散之 p-i-n 接面元件的暗電流顯著低於原生生長型元件，但因擴散過程在 p 型吸收層中缺陷產生，導致其響應度較低。
透過使用原生生長的 p-n 接面與縮小的 mesa 尺寸（約 3 μm），實驗成功展示了具有良好響應度（約 0.11 A/W）、寬頻寬（約 0.27 THz）、10 mA 飽和電流，以及在 0.27 THz 操作頻率下達到 -4 dBm 連續波（CW）輸出功率的元件表現。
透過調控反向偏壓，該元件展現出優異的偏置調變特性：僅需降低偏壓 1.2 V（從 −1.5 V 至 −2.7 V），其太赫茲輸出功率即可變動大於 20 dB 以上，頻率響應亦能由截止狀態迅速切換至高頻操作區域。此一明確且穩定的電調變能力，使其具備作為高速開關型光電元件（如光電混波器、脈衝調製器等）之潛力，未來應用前景可期。
;Due to the strong demanding of channel bandwidth for AI interconnect, the wideband (near dc to 300 GHz) measurements of optical-to-electrical (OE) and electrical-to-optical (EO) components or modules are highly desired. Compared with the traditional MMW techniques for wideband signal generation and transmission, by using the photonic approach, the banded and bulky frequency multipliers, cables, and waveguide adapters can be replaced by a low-weight fiber and a single ultrafast photodiode with high available power. Its O-E bandwidth and output power play vital role in the dynamic range performance.
In this thesis, we investigated the dynamic performances of ultrafast photodiode (PD) with different junction structure, which has Zn-diffusion and as grown p-n junction, respectively, to see which one can provide higher saturation power performance. The studied PD structure is a InP based uni-traveling carrier photodiode (UTC-PD) with the type-II GaAs0.5Sb0.5 (p)/In0.53Ga0.47As (i) hybrid absorber. With such absorber, its responsivity can be improved due to the narrowing of bandgap and an enhancement of photo-absorption process at the type-II interface.
Although the device with Zn-diffusion p-i-n junction exhibits a much lower dark current than that of the as-grown one, the diffusion one suffers a lower responsivity due to diffusion induced defects inside the p-type absorption regions.
By use of the as grown p-n junction with a miniaturized mesa size (~3 um), decent responsivity (~0.11 A/W), wide bandwidth (~0.27 THz), a 10 mA saturation current, and a continuous wave (CW) output power as high as -4 dBm at an operating frequency of 0.27 THz is successfully demonstrated.
By adjusting the reverse bias, the device demonstrates excellent bias modulation characteristics: with only a 1.2 V reduction in bias voltage (from −1.5 V to −2.7 V), the terahertz output power varies by more than 20 dB, and the frequency response can swiftly switch from a cutoff state to a high-frequency operational region. This clear and stable electrical modulation capability indicates its potential as a high-speed switching optoelectronic device, such as an optoelectronic mixer or pulse modulator, showing promising prospects for future applications. |
