鄭宇翔助理教授 於2011年獲得臺大電機系與物理系雙學位學士（獲八學期書卷獎），曾於2009年至美國伊利諾大學香檳分校交換一學期。2013年自臺大光電所碩士班畢業，指導教授為孫啟光教授。2019年取得美國麻省理工學院電機博士，指導教授為Prof. Keith Nelson。2019年加入臺大電機系及臺大電信所擔任助理教授，2025年加入臺大光電所。

鄭助理教授的研究領域為太赫茲電路元件以及超快光譜學。在太赫茲電路元件方面，著重於設計D band (110-170 GHz)及J band (220-330 GHz)的放大器、混頻器、倍頻器等主動電路晶片，以及設計天線、濾波器、耦合器等被動電路，更開發出世界第一套太赫茲縮距遠場晶片天線量測設備。在超快光譜學方面，實驗室專注於0.1-2 THz的穿透及反射頻譜量測，可以獲得材料的複數介電參數。鄭助理教授目前參與多項大型計畫，以6G無線通訊感測系統開發為主，也涉及無人機及衛星之通訊應用。

鄭助理教授截至2024年已發表十五篇期刊論文及五十一篇會議論文，其中包含六次學生論文獎、五次會議旅費補助及兩次新聞專題報導。2019年至2022年獲國立臺灣大學新聘特殊優秀人才獎勵。

除了研究教學外，鄭助理教授的興趣包含鐵人三項運動（游泳、自行車、跑步）、業餘無線電、書法等，也對動漫略有涉獵。鄭助理教授經營了一個YouTube channel，歡迎同學前往觀看。

Broadband InSe/MoS₂ Type-II Heterojunction Photodetector with Gate-Tunable Polarity

Professor Yuh-Renn Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 吳育任教授

The development of two-dimensional (2D) van der Waals heterojunctions has opened new possibilities for advanced optoelectronic devices, particularly in broadband photodetection. In this work, we demonstrate a broadband InSe/MoS₂ type-II heterojunction photodetector with gate-tunable polarity, enabling a near-linear wavelength-dependent photocurrent peak. The vertically stacked InSe/MoS₂ heterojunction exhibits broadband detection from 400 nm to 1064 nm, with a high responsivity of 10,200 A/W at 532 nm and −1430 A/W at 1064 nm, as well as a maximum photodetectivity of 3 × 10¹³ cm Hz^-1/2 W^-1. The device displays both positive and negative photoconductivity, depending on incident light energy, and a gate-tunable polarity transition at Vg = −20 V, which induces a photocurrent peak shifting nearly linearly with wavelength.

To gain deeper insight into the underlying mechanisms, we performed Poisson and drift-diffusion simulations to model the charge carrier dynamics within the InSe/MoS₂ heterojunction. As shown in Figure 2a, our simulations successfully reproduce the experimentally observed gate-tunable photocurrent peak. The calculated potential profile (Figure 2b) confirms the presence of a type-II band alignment, where electrons and holes accumulate at the heterojunction interface. Furthermore, the simulation results (Figure 2c) reveal that the photocurrent peak is governed by the balance between electron accumulation in MoS₂ and hole accumulation in InSe, which shifts with incident wavelength and power density. Notably, our simulations also explain the negative photoresponse under infrared illumination, attributed to trap-assisted interlayer charge transfer at the heterojunction interface (Figure 2h).

These findings demonstrate the potential of gate-tunable 2D heterojunctions for high-performance optoelectronic applications, such as tunable spectrometers, reconfigurable photodetectors, and integrated photonic circuits. The ability to control the device polarity and photoresponse via gate voltage provides new opportunities for designing multifunctional optoelectronic devices.

Reference:
Wenying Zhang, Kuan-Hao Chiao, Hsin-Wen Huang, Mohamed Abid, Cormac Ó Coileáin, Kuan-Ming Hung, Ching-Ray Chang, Yuh-Renn Wu,* and Han-Chun Wu*, "Broadband InSe/MoS₂ Type-II Heterojunction Photodetector with Gate-Tunable Polarity Induced Near-Linear Wavelength-Dependent Photocurrent Peak," ACS Applied Materials & Interfaces, 2025, 17, 12941−12951. DOI: 10.1021/acsami.4c22132.

Ultra-high thermal sensors based on quantum-well heterojunction bipolar transistors

Professor Chao-Hsin Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 吳肇欣教授

We are thrilled to share a groundbreaking achievement in the field of optoelectronics and high-speed device technology: the successful design and fabrication of the world’s first Darlington transistor utilizing cascaded Light-Emitting Transistors (LETs) with ultra-high thermal sensitivity.

Our research demonstrated that the single-quantum-well heterojunction bipolar transistor (SQW-HBT) exhibits a remarkable 73.23% increase in collector current (I_C) as the temperature rises from 25 ºC to 85 ºC under a base current (I_B) of 0.2 mA and a collector-to-emitter voltage (V_CE) of 2 V, a behavior contrasting the typical thermal response of conventional HBTs, as shown in Fig. 1(a) [1]. Building on these findings, we developed a modified charge-control model for multiple-quantum-well (MQW)-based HBTs, optimizing QW parameters such as number, size, width, position, and barrier width to enhance the efficiency of LETs for thermal sensor applications, as shown in Fig. 1(b) [2]. Using this model, we engineered triple-quantum-well (TQW)-HBTs that achieved a 200% increase in I_C as temperature rose from 25 ºC to 85 ºC at I_B of 1 mA and V_CE of 2 V, as shown in Fig. 1(c), marking a significant step toward high-temperature applications [3].

Leveraging these advancements, we designed a novel Darlington transistor by cascading two LETs. The LET alone demonstrated a 153% increase in I_C under temperature changes from 25 ºC to 85 ºC at I_B of 1 mA and V_CE of 4 V, while the Darlington transistor surpassed this performance, achieving a 210% increase in IC under similar conditions, as shown in Fig. 1(d). Notably, the current sensitivity of LETs reached 8.53 μA/ºC, and the Darlington transistor achieved an exceptional 26.2 μA/ºC. Additionally, the Darlington transistor reported a voltage sensitivity of 9.12 mV/ºC, significantly surpassing the performance of conventional thermal sensors [4]. Despite these achievements, challenges remain in achieving a highly linear voltage-to-temperature response due to nonlinear electron escape from the QW. To address these challenges, we proposed a QW size-dependent optimization model, achieving an optimal balance between thermal sensitivity and linearity for specific temperature ranges [5]. For instance, a QW width of 90 Å exhibited a thermal sensitivity of 1.34 mA/ºC and a linearity fitting parameter (B) of 0.67748 within a temperature range of 25 ºC to 100 ºC, as shown in Fig. 1(e).

Our team is committed to further modifying LET-based technologies to unlock their full potential as front-end components in smart thermal sensing applications. By optimizing QW structures, we aim to enhance linearity and sensitivity, paving the way for next-generation thermal sensor technologies with unprecedented performance. These achievements represent a significant leap forward in thermal-sensitive optoelectronic devices and hold immense promise for applications in smart sensing and beyond. We thank our collaborators and supporters for their contributions to this groundbreaking research.

Reference:
[1] M. Kumar, S.-J. Hsu, S.-Y. Ho, S.-W. Chang, and C.-H. Wu, “Current gain enhancement of heterojunction bipolar light-emitting transistor using staircase InGaAs quantum well,” IEEE Trans. Electron Devices, vol. 70, no. 10, pp. 5177-5183, Oct, 2023, doi:10.1109/TED.2023.3305355.
[2] M. Kumar, L.-C. Hsueh, S.-W. Cheng, S.-W. Chang, and C.-H. Wu, “Analytical modeling of current gain in multiple-quantum-well heterojunction bipolar light-emitting transistors,” IEEE Trans. Electron Devices, vol. 71, no. 1, pp. 343-349, Jan 2024, doi:10.1109/TED.2023.3289930.
[3] M. Kumar, S.-Y. Ho, S.-J. Hsu, P.-C. Li, S.-W. Chang, and C.-H. Wu, “Current gain enhancement at high-temperature operation of triple-quantum-well heterojunction bipolar light-emitting transistor for smart thermal sensor application,” IEEE Trans. Electron Devices, vol. 71, no.1, pp. 896-903, Jan. 2024, doi: 10.1109/TED.2023.3339084.
[4] M. Kumar, K.-Y. Hsueh, S.-J. Hsu, and C.-H. Wu, “Design and fabrication of novel Darlington transistor using light-emitting transistors for smart thermal sensor technology,” IEEE Electron Device Letters, vol. 45, no. 7, pp. 1365-1368, July, 2024, doi:10.1109/LED.2024.3401084.
[5] M. Kumar, S.-W. Chang, and C.-H. Wu, “Investigation of thermal sensitivity and linearity of quantum well-based heterojunction bipolar transistor,” IEEE Transactions on Electron Devices, Early Access, Nov 2024, doi: 10.1109/TED.2024.3492153.

— 資料提供：影像顯示科技知識平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃巖教授、郭權鋒 —

磁驅動光子“微型機器人”

可重構微光學元件具有許多應用，但其可調節性仍相當有限。可操縱的微型「機器人」具有可程式化功能，在微觀尺度上可以達到更好的光控制效果，這是一個誘人的概念。

康乃爾大學的Conrad Smart、Tanner Pearson和同事們展示了一種磁性可程式化和易操作的繞射微光學裝置（Science 386, 1031–1037; 2024）。

該結構採用深紫外光微影製程（Deep-ultraviolet lithography, DUV）和電子束微影（Electron beam lithography, EBL）以及各種沉積和蝕刻技術製造，長度範圍從毫米到奈米的元件組成，以便獲取機械、繞射和磁性特徵。作者將這些裝置稱為磁控顯微型機器人，或稱為「微型機器人（microbots）」。

該裝置透過利用薄膜機械中的奈米磁鐵（見圖1C）進行程式化，只需要毫特斯拉級（millitesla-scale）磁場即可驅動奈米厚度的樞軸（hinge）接頭（見圖1E），例如繞射面板。這種磁驅動也可用於實現裝置的大規模內部重新配置。

實驗架構展示了各種各樣的裝置，包括雙面板繞射裝置和使用許多元件的可調光學裝置。對於透鏡，焦距在沒有磁場時為50 μm，但可以調整到例如在10 mT磁場下為40 μm。該團隊能夠實現光機械超穎材料（optomechanical metamaterials）的運動並重構裝置形狀。

該論文作者之一Itai Cohen告訴《自然光子學》，該團隊過去五年一直致力於微型機器人研究。當他們意識到機器人的特徵足夠小以至於可以繞射光時，他們聯繫了Francesco Monticone並開始合作設計可以整合到他們的機器人平台中的光學元件。

「與先前的微型機器人相比，這些繞射機器人整合了光學元件，包括焦距可調的菲涅爾透鏡、能夠產生各種繞射圖案的繞射表面，以及可用於增強成像解析度的光柵。」Cohen解釋。「此外，由於它們非常柔順（柔軟），透過追蹤它們的變形，我們可以確定它們被壓在各種物體和材料上時所受到的力。這些性能對於該領域來說都是新的。」

Cohen認為，主要挑戰有兩個面向。首先是建構可作為樞軸的奈米級薄膜的能力。第二，涉及製造100奈米x50奈米單疇磁性（single-domain magnets）的技術。Cohen表示，這項技術之前已經被其他人發明，掌握這種製造流程並將其與團隊新開發的薄樞軸相結合，使他們能夠將磁性機器人縮小到單微米級（~5微米）。Cohen指出，薄樞軸和磁鐵的技術開發跨越了兩個博士學位，他強調，研究生Conrad Smart必須將所有技術整合在一起，進行測試和迭代設計，直到達到預期的結果。

除了對空間特徵進行成像之外，機器人還可以引導和聚焦光線。為了展示光束控制，作者研究團隊製作了具有磁可調週期的微觀繞射光柵（圖2A）。隨著施加磁場的增加，光柵面板被壓縮，透過移動一階繞射峰值來改變繞射圖案（圖2B）。這證明了透過機械驅動控制光束偏轉的能力。此外，繞射光柵表現出對微小力的敏感性，這由施加的磁擾動下繞射峰中的正弦振盪證明（圖2D），測得的力敏感性為1 pN。這些光柵還可以在表面上移動，從而實現移動、局部的光場控制（圖2C）。

擴展這一概念，作者研究團隊開發了一種磁可調繞射菲涅爾透鏡，具有連續可調焦距（圖2E）。與傳統的折射光學裝置不同，此變焦鏡頭利用磁致動器提供緊湊的設計。菲涅耳透鏡由徑向排列的梯形繞射面板組成，其焦距關係由公式決定。在外部磁場下，透鏡結構壓縮，焦距從50 μm減少到40 μm（圖2F）。該技術展示了開發可調繞射光學元件的一種有前景的方法，為自適應和小型化光學系統鋪平了道路。

展望未來，該團隊正在努力將其中一些功能整合到他們的電子驅動機器人中。Cohen告訴《自然光子學》雜誌：「這種積體化使我們能夠用光來控制機器人，而不是用目前用於產生驅動機器人的磁場的六極磁鐵。」「我們正在致力於設計更複雜的光學元件。最後，我們還希望將這些機器人與光纖結合起來，使外科醫生能夠更輕鬆地對現場環境進行成像。」