鍺量子點及鍺基板光偵測器

Germanium Quantum Dots and Bulk Germanium Photodetector

張傑竣(Chieh-Chun Chang)

指導教授 ： 劉致為

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.10130

摘要

本論文中，我們提出利用金氧半穿隧二極體中穿隧閘極電流的特性來製作光偵測器。為了提升光偵測器的光響應，我們使用硼原子delta摻雜在量子點與量子井光偵測器中。藉由在鍺量子點、量子井或矽間隔層中加入p型的delta摻雜來增加電洞濃度，可以顯著提升紅外光波段的光響應。雙頻譜寬帶的吸收亦可以藉由在矽間隔層中加入delta的硼原子摻雜來達成，其在波長3.7-6微米波段產生的波峰，是由鍺量子點內子能帶間的躍遷(intersubband transition)所造成；另一個在波長6-16微米波段的波峰是由矽間隔層裡的硼原子delta摻雜形成的位能井之能帶內躍遷(intraband transition)所造成。由於在大氣中波長3-5.3微米與7.5-14微米的波段有很高的穿透率，這使得我們的元件很適合應用在雙頻譜偵測中。另外，在鍺量子點內與Si0.9Ge0.1量子井內加入delta摻雜亦在本論文中有所研究，以用來確認吸收頻譜產生的來源。鍺量子點與鍺量子井光偵測器操作在15 K低溫、閘極電壓1 V情況下的光響應分別為0.03 mA/W與1.3mA/W。量子點元件的光響應在波長3.5-5微米的波段可以操作至100 K，但量子井元件的光響應在波長3-7微米的波段僅能操作至60 K，這是由於量子井光偵測器相較於量子點光偵測器有較高的暗電流(因其有較低的躍遷能量)，故限制住了量子井光偵測器的操作溫度。
由於鍺具有吸收紅外光的能力使它很有潛力成為高性能光偵測器。本論文中，我們主要研究鍺基板—金氧半—光偵測器之特性。我們應用金屬閘極技術來減少元件操作在逆向偏壓下的漏電流，且在這個結構中的閘極氧化層是用低溫液相沉積法所成長，可以使照光產生的載子藉由多層缺陷的協助而穿過氧化層，並可避免高溫製程對矽鍺結構造成損害。對PMOS元件操作在反轉區域下，電流主要來自於鋁電極中的電子穿隧至n型半導體區域，因此和NMOS元件相比，電流提高了許多。在實驗中，鍺基板—金氧半—光偵測器操作在1310奈米的光波長下具有高效率和高光響應，並同時可工作在635、850、1310與1550 奈米的光波長下，很適合運用於光纖通訊上。若再藉由外加機械應變的方式，我們可以減小鍺材料的等效能隙，進而增加照光所激發的載子數目；由於有較多的載子被激發，偵測器的光電流與光響應都可以被顯著地提升。在施加0.32 %的雙軸張應力之機械應變後，鍺基板—金氧半結構之元件操作於波長635、1310與1550奈米的波段，其對應之光響應分別為25 mA/W、210 mA/W與17 mA/W。

關鍵字

鍺 ； 金氧半 ； 量子點 ； 量子井 ； 光偵測器

並列摘要

In this thesis, the novel MOS tunneling diodes with high leakage current were utilized as photodetectors. In order to increase the responsivity, boron delta-doping was used in the QDIPs and QWIPs. The infrared response was significantly enhanced due to the p-type delta-doping in Ge QDs/QWs or in Si spacers because of the increase of hole concentration. The two-color broadband absorption of MOS Ge/Si QDIPs were demonstrated using boron delta-doping in the Si spacers. The peak at 3.7-6 um is due to the intersubband transition in the Ge QD layers. The other peak at 6-16 um mainly comes from the intraband transition in the boron delta-doping wells in the Si spacers. Since the atmospheric transmission windows locate at 3-5.3 um and 7.5-14 um, the two-color detection is feasible using this device. The delta-doping in Ge QDs and Si0.9Ge0.1 QWs were also investigated to identify the origin of the absorption. The peak responsivity of the QDIP and the QWIP at 15 K was found to be 0.03 mA/W and 1.3 mA/W, respectively, at a gate voltage of 1 V. The QD photoresponse in the peak wavelength range 3.5-5 um can be measured up to 100 K, while that for QW 3-7 um can only be detected up to 60 K. A higher dark current due to the lower transition energy in the QWIP limits its operating temperature as compared to the QDIP.
Since the ability of Ge to absorb in the near infrared makes it an interesting candidate for high-performance photodetector applications. Thus, the bulk Ge MOS photodetectors were also studied in this thesis. The leakage current at inversion bias was reduced by metal gate technique, and the oxide of bulk Ge MOS photodetectors was grown by LPD to reduce the thermal budget that carriers can tunnel through oxide via the assistance of multiple traps. In experiment, the novel bulk Ge PMOS photodetectors has high quantum efficiency and high responsivity at 1310 nm. Besides, the bulk Ge MOS detector can operate under 635 nm, 850 nm, 1310 nm, and 1550 nm lightwave exposure and can be applied to the optical-fiber communications. By applying external mechanical strain, we can reduce the effective bandgap of Ge and increase the photo-generated carriers. Thus, photocurrent and responsivity of the detector were significantly enhanced because more photo-generated carriers were excited. After applying 0.32% biaxial tensile strain, the bulk Ge MOS device can detect the wavelengths of 635 nm, 1310 nm, and 1550 nm with the responsivity of 25 mA/W, 210 mA/W, and 17 mA/W, respectively.

並列關鍵字

Ge ； MOS ； QDIP ； QWIP ； Photodetector

參考文獻

[13] K. Rajendran and W. Schoenmaker, “Studies of boron diffusivity in strained Si1–xGex epitaxial layers,” J. Appl. Phys., vol. 89, pp. 980-987, 2001.

Chapter 1

[1] S. M. Sze, ”Physics of Semiconductor Devices”, 2nd edition, pp.743.

[2] J., Kolodzey, T.N., Adam, R.T., Troeeger, P.-C., Lv, S.K., Ray, G., Looney, A., Rosen, M.S., Kagan, Irina N., Yassievich, ‘‘The Design and Operation of TeraHertz Sources Based on Silicon Germanium Alloys,’’ Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, 9 –11th April, 2003, Grainau, Germany.

Proskuryakov, J. Appl. Phys. 89 (2001) 5676.