近年來，短波紅外光偵測器在光纖通訊、光學雷達與生醫感測等領域的需求日益提升。其中，鍺與鍺錫合金因具備與矽製程高度相容的特性，並可透過調控錫含量以延展其光吸收截止波長，成為發展新一代紅外光偵測器之潛力材料。在半導體元件製程中，載子的導入通常需仰賴摻雜技術。雖然離子佈植因具備良好的控制性與製程效率而被廣泛採用，然而其常伴隨摻雜深度不均及熱退火擴散等問題，對於元件微縮與界面品質造成限制。相較之下，原位摻雜技術具備成為替代方案的潛力，可結合分子束磊晶(MBE)或金屬有機化學氣相沉積(MOCVD)等方法，利用固體金屬靶材或氫化前驅物進行摻雜。本研究則首度採用鎵與銻之氯化前驅物，結合電漿輔助化學氣相沉積(PECVD)技術，成功製備出具有高載子濃度的鍺摻雜薄膜。
實驗中以氫氣作為載氣，選用常溫下性質穩定且無毒的三氯化鎵(GaCl₃)、三氯化銻(SbCl₃)與四氯化鍺(GeCl₄)作為前驅物，實現鎵與銻元素於鍺薄膜中的摻雜。薄膜中載子濃度之定量分析係透過霍爾量測與熱點探針量測完成，並作為元件摻雜層設計的依據。本製程首次以氯化前驅物結合電漿輔助化學氣相沉積(PECVD)技術，成功製備出高鎵或高銻摻雜濃度之鍺薄膜。
摻雜銻之鍺薄膜可達最高載子濃度為1.5×10¹⁹ cm⁻³，對應薄膜厚度為200奈米，表面方均根粗糙度(RMS)小於1奈米，且其X射線繞射(XRD)分析顯示鍺(100)晶向之半高寬(FWHM)小於0.1°。研究亦歸納出前驅物溫度、流量比、氬氣導入、電漿功率與鍍膜溫度等製程參數對載子濃度的影響，結果顯示，在鍍膜溫度 400 °C 與電漿功率130 W 下可有效提升載子濃度，同時兼顧薄膜品質。此外，針對鍺薄膜摻雜鎵的製程，發現須額外導入氬氣以促進鎵的摻雜反應，克服鎵在薄膜中難以有效摻入的問題。以摻雜鎵之鍺薄膜製作之光偵測器，於 0.9–1.8 μm 波段可達到約 0.003 A/W的響應率。此響應率與以硼離子佈植製備、載子濃度為5×1018 cm-3之鍺薄膜所製作之光偵測器相當，顯示以鎵摻雜鍺薄膜製作元件具備實用可行性。

In recent years, the demand for short-wave infrared (SWIR) photodetectors has increased significantly in fields such as optical communication, LiDAR, and biomedical sensing. Among the candidate materials, germanium (Ge) and germanium-tin (GeSn) alloys have emerged as promising options due to their compatibility with silicon-based processes and the tunable cutoff wavelength of GeSn via Sn content adjustment. Carrier introduction in semiconductor device fabrication typically relies on doping technologies. While ion implantation offers excellent control and process efficiency, it often suffers from drawbacks such as non-uniform doping profiles and thermal diffusion during annealing, which limit device scaling and interface quality. In contrast, in-situ doping techniques offer the potential to become an alternative, utilizing solid metal targets or hydrogenated precursors in conjunction with methods such as molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). This study, for the first time, successfully fabricated antimony(Sb) or gallium(Ga)-doped germanium thin films with high carrier concentrations using antimony chloride or gallium chloride precursors in conjunction with plasma-enhanced chemical vapor deposition (PECVD).
In the experiment, hydrogen was used as the carrier gas, and gallium trichloride (GaCl₃), antimony trichloride (SbCl₃), and germanium tetrachloride (GeCl₄), all stable and non-toxic at room temperature, were selected as precursors to achieve Sb or Ga-doped germanium thin films. Quantitative analysis of the carrier concentration in the film was achieved through Hall effect measurement and hot probe measurements, which served as a basis for device doping layer design. This process is the first to successfully produce germanium thin films with high Ga or Sb doping concentrations using chloride precursors combined with PECVD technology.
The Sb-doped Ge films achieved carrier concentration of 1.5×10¹⁹ cm⁻³ with a film thickness of 200 nm, root-mean-square surface roughness (RMS) below 1 nm, and a Ge(100) X-ray diffraction full width at half maximum (FWHM) less than 0.1°. The study also analyzed the effects of process parameters such as precursor temperature, flow rate, argon gas introduction, plasma power, and deposition temperature on carrier concentration. The results showed that a deposition temperature of 400°C and a plasma power of 130W effectively increased carrier concentration while maintaining film quality. For Ga-doped Ge films, introducing additional argon gas was found essential to enhance Ga incorporation, addressing challenges in Ga activation within the film. Photodetectors fabricated from Ga-doped Ge films demonstrated a responsivity of approximately 0.003 A/W in the 0.9–1.8 μm wavelength range, comparable to those made from boron-implanted Ge films with a carrier concentration of 5×10¹⁸ cm⁻³. These results confirm the practical feasibility of fabricating infrared photodetectors using in-situ Ga-doped Ge films via chloride-precursor-based PECVD.