本論文旨在進行一種具硒化鍺(GeSe)覆蓋層氧化銦鎵鋅(IGZO)薄膜電晶體紅外光檢測器光電特性之模擬分析，透過p型GeSe覆蓋層一方面作為紅外光照射下之主動層拓展光響應波長範圍，一方面利用其與n-IGZO所形成異質接面(heterojunction, HJ)提供背通道表面一額外空乏區，允許採用較厚IGZO通道於提升光電流(Iph)同時抑制暗電流(Idark)，減輕Iph與Idark間於提升通道膜厚所產生之消長關係。
當半導體材料吸收足夠能量光子時，電子獲得能量從價帶躍遷至導帶，形成光生電子電洞對，提升半導體載子濃度與導電率，光電晶體即利用半導體這一光敏特性，藉由汲極-源極之間橫向電場作用，進行光生載子之收集。值得一提的是，光電流大小受限於半導體通道的體積限制，因此，當覆蓋層堆疊於背通道表面時，可增加通道厚度並提供額外的光生電子，使元件光電流獲得進一步提升。因此，本論文將針對通道覆蓋層對元件光電特性的改善，從元件能帶圖、電位、電流跟載子濃度分別探討其中的原因。
本論文主要集中於下閘極結構之傳統IGZO TFT，命名為Type A TFT，與具GeSe覆蓋層之Type A TFT，稱Type B TFT，兩種元件光電特性之模擬分析研究。本論文所使用之半導體元件模擬軟體為Sentaurus TCAD，在Sentaurus TCAD中，首先使用SDE軟體設計元件結構與網格大小，再使用SDEVICE軟體添加物理模型與偏壓設定，最後使用INSPECT萃取電性參數。本論文於SCEVICE中使用漂移-擴散傳輸模擬(Drift-diffusion model, DD model)模擬元件內部的電子與電洞傳導模式，於復合模型中增加SRH復合與歐傑復合(Auger recombination)，於通道漏電電流中增加帶到帶穿透(BTB Tunneling Model)模型以模擬電極接面處通道漏電電流。根據材料設定不同的載子移動率，並考慮氧化層電導，加入Conductive Insulators Models，計算通道與氧化層之間的閘極漏電電流；照光所採用的求解器為Optical Beam Absorption Method，使用Beer’s law進行光子吸收的模擬。
本論文之研究內容計分為「傳統IGZO TFT光電特性」與「具GeSe覆蓋層結構IGZO TFT光電特性」兩個部分，茲依序簡述如下:
於第一部分「傳統IGZO TFT光電特性」研究方面，首先依據模擬所得熱平衡能帶圖、電位分布與電荷分布，探討通道厚度(Tch)、通道雜質摻雜濃度(Nch)與閘極金屬功函數(ϕm)等結構參數對傳統TFT熱平衡下通道全空乏程度與電特性關係之影響。模擬結果顯示，當T_ch並非足夠薄時，如Tch=70 nm之Type A1-70 TFT，因閘極與通道半導體功函數差不足以使背通道表面區域空乏，於是未空乏的背通道區域即成為通道漏電電流來源。於考慮帶到帶穿透模式下(BTB Tunneling Model)的閘極漏電電流下，此一元件暗電流Ioff(4.52×10^(-9) A/μm)大增，遠大於通道厚度30 nm的Type A1-30 TFT之Ioff(4.15×10^(-12) A/μm)。當通道摻雜濃度從5×10^16 cm^(-3)調變至5×10^17 cm^(-3)，模擬結果顯示，對Type A1-30 TFT而言，隨通道濃度增加，通道空乏程度降低使元件越容易導通，Von與Vth負移(0.18 V→-2.54 V ,0.5 V→-0.42 V)，使Ioff與Ion兩者皆有明顯提升(3.46×10^(-12) A/μm→4.17×10^(-9) A/μm,2.42×10^(-5) A/μm→3.80×10^(-5) A/μm)，然Ioff的增加幅度大於Ion，造成Ion/Ioff隨著通道濃度增加而降低(6.99×10^6→9.11×10^3)。當閘極金屬功函數從4 V調變至5.4 V時，模擬結果顯示，閘極功函數增加使通道空乏程度提高，Von與Vth正移(-0.96 V→0.44 V, -0.61 V→0.79 V)，Vth的正移造成Ion下降，從4.10×10^(-5) A/μm降至2.12×10^(-5) A/μm。
於300 nm波長光照射下，模擬結果顯示，Type A1-30 TFT之光響應度(Rph)、光靈敏度(Sph)與偵測度(D*)分別為749.52 A/W、1.81×10^4 A/A與6.50×10^13 Jones。隨著Tch增加，Rph也隨之增加，但因同時Ioff也大幅度增加造成Sph與D*的下降，導致Type A1-70 TFT雖然擁有最大Rph=5625.35 A/W，但Sph與D*卻分別下降至1.43×10^2 A/A與1.58×10^13 Jones，皆為Type A1 TFTs之中最低者，顯示傳統IGZO TFT於Ioff 與Iph具有嚴重的消長(trade-off)關係。
為改善Ioff 與Iph 之間的消長關係並進行紅外光感測應用，本研究於IGZO背通道表面堆疊一層較低能隙寬度的GeSe覆蓋層，除拓展光偵測波長範圍外，可利用其與IGZO通道建構之異質接面於背通道區域形成一空乏區，允許於增加Tch下仍可維持通道的全空乏狀態抑制暗電流，並利用照光下pn異質接面空乏區推動光生電子進入通道提升光電流。於本研究第二部份模擬分析上，首先針對GeSe覆蓋層的長度對通道厚度為40 nm元件光電特性影響之探討，分別比較GeSe覆蓋層長度(LCL) 0.8、0.6、0.4與0.2 μm的Type (B1~B4)-100 TFTs的光電特性。模擬結果顯示，隨LCL漸少，300 nm波長的Rph由988.67 A/W增加到1317.46 A/W，而900 nm波長的Rph由3.79 A/W下降到0.01 A/W，此可歸因於GeSe覆蓋層對300 與900 nm光源的吸收差異，而IGZO通道層僅吸收300 nm光源所致。於紅外光波長(900 nm)的部分，其光響應主要來自GeSe覆蓋層，因此光響應的大小與GeSe覆蓋層的受光面積與厚度呈正向關係，導致Type B1-100 TFT於900 nm下光響應優於Type B4-100 TFT。
於GeSe覆蓋層厚度對於元件光感測性能之影響模擬分析部分，模擬結果顯示，於300 nm光源照射下，光響應隨著覆蓋層厚度減少(從200 nm減至9 nm)，從Type B1-200 TFT的15.79 A/W增加到Type B1-9 TFT的最大值2745.40 A/W。而於900 nm光源照射下，光響應從Type B1-200 TFT之3.15 A/W開始增加，於Type B1-60 TFT達最大值的4.04 A/W，此可歸因於300 nm下入射光照射下的光生載子集中在GeSe覆蓋層上表面中性區吸收復合，無法進入通道為電極收集形成光電流。隨著GeSe覆蓋層厚度減少，允許較大比率的光生電子進入通道被吸收，造成更大的光響應。然於900 nm光照射下，只有GeSe覆蓋層能夠吸收光子，於元件結構設計應使入射光子皆為覆蓋層空乏區所吸收，以產生電子供應通道產生光電流，故需有足夠大的空乏區與較薄的中性區，此即Type B1-60 TFT展現最佳紅外光響應之主因。
本論文所提出具硒化鍺覆蓋層氧化銦鎵鋅薄膜電晶體，模擬結果顯示可有效減緩Idark與Iph消長關係，除可提升300 nm波長的光響應特性外，亦可藉GeSe覆蓋層拓展光響應波長範圍，於900 nm波長照射下，Rph可達4.04 A/W，證實覆蓋層確實提供紅外光感測更能及提升光響應之效益。本論文提出之具覆蓋層TFTs通道在未來IR-PD應用上極具創新性與發展性，預期可對光感器產業於先進紅外光感測器之開發提供助益。

The simulation of infrared photodetector (IR-PDs) based on IGZO thin-film transistors (TFTs) with a GeSe capping layer (CL) was carried out in this study. The simulation results that were obtained using Sentaurus TCAD are presented and discussed. The presence of high mobility and a wide bandgap in IGZO TFTs leads to good UV light sensing performance with visible light blindness. The GeSe CL and IGZO channel form a pn heterojunction, allowing for a thicker channel without compromising off-state current. Moreover, the GeSe capping layer can extend the wavelength range of photosening response. Simulation results demonstrate that Type B1-9 TFT has high photoresponsivity (2745.40 A/W), photosensitivity (1.09×10^5 A/A) and specific detectivity (3.08×10^14 Jones), which are about 1.78×, 3.61× and 2.57× higher than a traditional 40-nm-thick IGZO TFT without CL under 300 nm UV irradiation. Furthermore, the GeSe capping layer extends the photoresponse wavelength range, leading to a photoresponsivity of 4.04 A/W, a photosensitivity of 1.61×10^2 A/A and a specific detectivity of 4.51×10^11 Jones.

[1] M. Bembenek et al., "Optical and mechanical properties of layered infrared interference filters," Sensors, vol. 22, no. 21, Oct. 2022, Art. no. 8105.
[2] A. Rogalski, "History of infrared detectors," Opto-electronics review, vol. 20, pp. 279-308, Jul. 2012.
[3] M. Ferrari and V. Quaresima, "Near infrared brain and muscle oximetry: from the discovery to current applications,"Journal of Near Infrared Spectroscopy, vol. 20, no. 1, pp. 1-14, Jan. 2012.
[4] B. B. Lahiri, S. Bagavathiappan, T. Jayakumar, and J. Philip, "Medical applications of infrared thermography: a review," Infrared physics & technology, vol. 55, no. 4, pp. 221-235, Jul. 2012.
[5] S.-R. Tsai and M. R. Hamblin, "Biological effects and medical applications of infrared radiation," Journal of Photochemistry and Photobiology B: Biology, vol. 170, pp. 197-207, May 2017.
[6] A. A. Bunaciu, V. D. Hoang, and H. Y. Aboul-Enein, "Applications of FT-IR spectrophotometry in cancer diagnostics," Critical reviews in analytical chemistry, vol. 45, no. 2, pp. 156-165, Jan. 2015.
[7] Y. Luo, J. Remillard, and D. Hoetzer, "Pedestrian detection in near-infrared night vision system," in 2010 IEEE Intelligent Vehicles Symposium, San Diego, CA, USA, Jun. 2010, pp. 51-58.
[8] A. M. Waxman et al., "Color night vision: fusion of intensified visible and thermal IR imagery," in Proc. SPIE 2463, Synthetic Vision for Vehicle Guidance and Control, Orlando, FL, USA, Jun. 1995, pp. 58-68.
[9] Y. Pérez, E. Pastor, E. Planas, M. Plucinski, and J. Gould, "Computing forest fires aerial suppression effectiveness by IR monitoring,"Fire Safety Journal, vol. 46, no. 1-2, pp. 2-8, Jan. 2011.
[10] L. Jun, T. Qiulin, Z. Wendong, X. Chenyang, G. Tao, and X. Jijun, "Miniature low-power IR monitor for methane detection," Measurement, vol. 44, no. 5, pp. 823-831, Jun. 2011.
[11] A. A. Tronin, M. Hayakawa, and O. A. Molchanov, "Thermal IR satellite data application for earthquake research in Japan and China," Journal of Geodynamics, vol. 33, no. 4-5, pp. 519-534, May 2002.
[12] Gómez-Chova, Luis, et al. "Multimodal classification of remote sensing images: A review and future directions." Proceedings of the IEEE, vol. 103, no. 9, pp. 1560-1584, Aug. 2015.
[13] T. Chen, S.-J. Young, S. Chang, and C. Hsiao, "Photoconductive gain of vertical ZnO nanorods on flexible polyimide substrate by low-temperature process," IEEE 163 Sensors Journal, vol. 11, no. 12, pp. 3457-3461, Dec. 2011.
[14] Y. Liu et al., "Visible-blind photodetectors with Mg-doped ZnO nanorods," IEEE Photonics Technology Letters, vol. 26, no. 7, pp. 645-648, Apr. 2014.
[15] A. Rogalski, "Infrared detectors: an overview," Infrared physics & technology, vol. 43, no. 3-5, pp. 187-210, Apr. 2002.
[16] A. de Jamblinne de Meux, A. Bhoolokam, G. Pourtois, J. Genoe, and P. Heremans, "Oxygen vacancies effects in a‐IGZO: Formation mechanisms, hysteresis, and negative bias stress effects," physica status solidi (a), vol. 214, no. 6, Mar. 2017, Art. no. 1600889.
[17] K.-H. Bae, M. G. Shin, S.-H. Hwang, H.-S. Jeong, D.-H. Kim, and H.-I. Kwon, "Electrical Performance and Stability Improvement of p-Channel SnO Thin-Film Transistors Using Atomic-Layer-Deposited Al₂O₃ Capping Layer," IEEE Access, vol. 8, pp. 222410-222416, Dec. 2020.
[18] H. Sun et al., "Mobility and Current Boosting of In-Ga-Zn-O thin-film transistors with Metal Capping Layer Oxidation," Nanotechnology, June 2024, Art. no. 355202.
[19] H. Yoo et al., "High photosensitive indium–gallium–zinc oxide thin-film phototransistor with a selenium capping layer for visible-light detection," ACS applied materials & interfaces, vol. 12, no. 9, pp. 10673-10680, Feb. 2020.
[20] H. Ferhati, F. Djeffal, and L. Drissi, "Enhanced infrared photoresponse of a new InGaZnO TFT based on Ge capping layer and high-k dielectric material,"Superlattices and Microstructures, vol. 156, Jun. 2021, Art. no. 106967.
[21] S. W. Pak, D. Chu, S. K. Lee, and E. K. Kim, "Enhancement of near-infrared detectability from InGaZnO thin film transistor with MoS2 light absorbing layer," Nanotechnology, vol. 28, no. 47, Oct. 2017, Art. no. 475206.
[22] H. Ferhati, F. Djeffal, and L. Drissi, "Performance analysis of a new Mid-Infrared phototransistor based on combined graded band gap GeSn sensitive-film and IGZO TFT platform," Micro and Nanostructures, vol. 173, Dec. 2023, Art. no. 207467.
[23] Ü. Özgür, D. Hofstetter, and H. Morkoc, "ZnO devices and applications: a review of current status and future prospects," Proceedings of the IEEE, vol. 98, no. 7, pp. 1255-1268, May. 2010.
[24] H. Hosono, "Ionic amorphous oxide semiconductors: Material design, carrier transport, and device application," Journal of non-crystalline solids, vol. 352, no. 9-20, pp. 851-858, Apr. 2006.
[25] P. Chen et al., "GeSe/MoTe2 vdW heterostructure for UV–VIS–NIR photodetector with fast response," Applied Physics Letters, vol. 121, Art. no. 021103, Jul. 2022.
[26] S.-C. Liu et al., "An antibonding valence band maximum enables defect-tolerant 164 and stable GeSe photovoltaics," Nature communications, vol. 12, no. 1, Jan. 2021, Art. no. 670.
[27] S.-C. Liu, Y. Yang, Z. Li, D.-J. Xue, and J.-S. Hu, "GeSe thin-film solar cells," Materials Chemistry Frontiers, vol. 4, no. 3, pp. 775-787, Dec. 2019.
[28] Buckley, Jannise J., et al. "Synthesis and Characterization of Ternary Sn x Ge1–x Se Nanocrystals." Chemistry of Materials, vol. 24, no. 18, pp. 3514-3516, Aug. 2012.
[29] S. C. Liu et al., "Investigation of physical and electronic properties of GeSe for photovoltaic applications," Advanced Electronic Materials, vol. 3, no. 11, Jun. 2017, Art. no. 1700141.
[30] K. Zeng, D.-J. Xue, and J. Tang, "Antimony selenide thin-film solar cells," Semiconductor science and technology, vol. 31, no. 6, Apr. 2016, Art. no. 063001.
[31] X. Wang et al., "Short-wave near-infrared linear dichroism of two-dimensional germanium selenide," Journal of the American Chemical Society, vol. 139, no. 42, pp. 14976-14982, Sep. 2017.
[32] H. Zhao et al., "Band structure and photoelectric characterization of GeSe monolayers," Advanced Functional Materials, vol. 28, no. 6, Dec. 2018, Art. no. 1704855.
[33] Z. Yang et al., "WSe2/GeSe heterojunction photodiode with giant gate tunability," Nano Energy, vol. 49, pp. 103-108, 2018.
[34] X. Zhou et al., "Highly anisotropic GeSe nanosheets for phototransistors with ultrahigh photoresponsivity," Advanced science, vol. 5, no. 8, Apr. 2018, Art. no. 1800478.
[35] D. J. Xue, J. Tan, J. S. Hu, W. Hu, Y. G. Guo, and L. J. Wan, "Anisotropic photoresponse properties of single micrometer-sized GeSe nanosheet," Advanced Materials (Deerfield Beach, Fla.), vol. 24, no. 33, pp. 4528-4533, Jul. 2012.
[36] Y. Yang et al., "Air-stable in-plane anisotropic GeSe2 for highly polarizationsensitive photodetection in short wave region," Journal of the American Chemical Society, vol. 140, no. 11, pp. 4150-4156, Mar. 2018.
[37] L. Liu et al., "High selective gas detection for small molecules based on germanium selenide monolayer," Applied Surface Science, vol. 433, pp. 575-581, Mar. 2018.
[38] D.-J. Xue et al., "GeSe thin-film solar cells fabricated by self-regulated rapid thermal sublimation," Journal of the American Chemical Society, vol. 139, no. 2, pp. 958-965, Dec. 2017.
[39] B. Chen et al., "Magnetron sputtering deposition of GeSe thin films for solar cells," Solar Energy, vol. 176, pp. 98-103, Jun. 2018.
[40] B. Chen et al., "Highly oriented GeSe thin film: self-assembly growth via the sandwiching post-annealing treatment and its solar cell performance," Nanoscale, 165 vol. 11, no. 9, pp. 3968-3978, Feb. 2019.
[41] T. Lyu et al., "Advanced GeSe-based thermoelectric materials: Progress and future challenge," Applied Physics Reviews, vol. 11, no. 3, Sep. 2024.
[42] H. Wiedemeier and P. Siemers, "The thermal expansion and high temperature transformation of GeSe," Zeitschrift für anorganische und allgemeine Chemie, vol. 411, no. 1, pp. 90-96, Jan. 1975.
[43] T. He et al., "Extrinsic photoconduction induced short‐wavelength infrared photodetectors based on Ge‐based chalcogenides," Small, vol. 17, no. 4, Dec. 2021, Art. no. 2006765.
[44] S. Lee, and A. Nathan, "Conduction Threshold in Accumlation-Mode InGaZnO Thin Film Transistors," Scientific Reports, vol. 6, Mar. 2016, Art. no. 22567.
[45] M. Nakata et al., "Influence of oxide semiconductor thickness on TFT characteristics," in 2012 19th International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), Jul. 2012, IEEE, pp. 43-44.
[46] C. H. Kim, K.-S. Sohn, and J. Jang, "Temperature dependent leakage currents in polycrystalline silicon thin film transistors," Journal of applied physics, vol. 81, no. 12, pp. 8084-8090, Jun. 1997.
[47] S. Yu, X. Guan, and H.-S. P. Wong, "Conduction mechanism of TiN/HfOx/Pt resistive switching memory: A trap-assisted-tunneling model," Applied Physics Letters, vol. 99, Aug. 2011, Art. no. 063507.
[48] J. S. Lee, S. Chang, H. Bouzid, S. M. Koo, and S. Y. Lee, "Systematic investigation on the effect of contact resistance on the performance of a‐IGZO thin‐film transistors with various geometries of electrodes," physica status solidi(a), vol. 207, no. 7, pp. 1694-1697, Jul. 2010.
[49] S.-H. Bae, H.-J. Ryoo, J.-H. Yang, Y.-H. Kim, C.-S. Hwang, and S.-M. Yoon, "Influence of reduction in effective channel length on device operations of In-Ga-Zn-O thin-film transistors with variations in channel compositions," IEEE Transactions on Electron Devices, vol. 68, no. 12, pp. 6159-6165, Oct. 2021.
[50] P. Cadareanu and P.-E. Gaillardon, "A TCAD simulation study of threeindependent-gate field-effect transistors at the 10-nm node," IEEE Transactions on Electron Devices, vol. 68, no. 8, pp. 4129-4135, Jun. 2021.
[51] P. Pfäffli et al., "TCAD modeling for reliability," Microelectronics Reliability, vol. 88, pp. 1083-1089, Oct. 2018.
[52] Sentaurus TCAD User Manual Document ver. L-2022.03, Mountain View, CA, USA, 2022.
[53] Liu, Shun‐Chang, et al. "Tuning the optical absorption property of GeSe thin films by annealing treatment." physica status solidi (RRL)–Rapid Research Letters, vol. 12, no. 12, Oct. 2018, Art. no. 1800370.
[54] A. Galca, G. Socol, and V. Craciun, "Optical properties of amorphous-like indium 166 zinc oxide and indium gallium zinc oxide thin films," Thin Solid Films, vol. 520, no. 14, pp. 4722-4725, Nov. 2011.
[55] X. Zou et al., "Enhanced performance of a-IGZO thin-film transistors by forming AZO/IGZO heterojunction source/drain contacts," Semiconductor science and technology, vol. 26, no. 5, Mar. 2011, Art. no. 055003.
[56] Amudhavalli, B., R. Mariappan, and M. Prasath. "Synthesis chemical methods for deposition of ZnO, CdO and CdZnO thin films to facilitate further research." Journal of Alloys and Compounds 925 (2022): 166511.