超高真空化學氣相沉積系統成長之矽與矽鍺量子井結構物理及其元件應用

Abstract

本論文中，我們利用超高真空化學氣相沉積系統 (UHV/CVD)， 在 600 到 475 ℃ 的溫度範圍中成長矽磊晶及受應力的矽鍺合金磊晶層 (Strained Si1-xGex alloy epitaxial layer)。並利用成長之高品質的矽與矽鍺磊 晶層，深入探討矽與矽鍺量子井異質結構的物理特性，及其在元件上應用 ，包括 p-型選擇性摻雜場效電晶體與 p-型量子井遠紅外線光偵測器。 在磊晶層成長方面，我們已成功地沉積品質優良的矽磊晶及受應力的矽鍺 合金磊晶層，及受應力的矽與矽鍺超晶格 (Strained Si/Si1-xGex superlattice)。從矽與矽鍺合金磊晶層之高解析度雙晶體 X 光繞射光譜 的測量結果，得到在同一片晶圓上鍺含量的最大與最小偏差值是0.2 % ， 平均均勻率是 0.75 %。硼摻雜之矽磊晶及矽鍺合金磊晶層中硼濃度可達 到 4.0 x 1021 至1.0 x 1021 cm-3，此硼濃度遠高於硼在矽磊晶及矽鍺 合金磊晶層的固體溶解度，約數倍至數十倍以上。SIMS 測量結果發現於 575 至 525℃成長時沒有鍺堆積在矽與矽鍺介面上的情形。X 光反射光譜 (XRR)及高解析度雙晶體 X 光繞射光譜 (HRXRD) 用來得出矽與矽鍺超晶 格的結構參數。由XRR 測量結果得到矽與矽鍺的介面平整度在 525℃成長 時皆為 0.1 nm，而在 550℃ 成長時皆為 0.2 nm。在相同的氣體成分成 長時，發現矽與矽鍺超晶格中的鍺含量隨著磊晶厚度增加而增加。一個簡 單的模型被提出用以解釋這個現像；從此模型可得到過渡區的厚度與過渡 的時間。在 550℃ 成長時，過渡區的厚度為1.01 至 1.46 nm 對於不同 的氣體成分成長；而在 525℃ 成長時，過渡區的厚度為0.34 至 0.66 nm 。我們得到的結論是，利用超高真空化學氣相沉積系統 (UHV/CVD) 成長 微細結構時，鍺含量在介面的陡峭度由成長中表面氫的覆蓋度來決定；及 兩個限制成長速率的過程之競爭，導至一個複雜的趨勢成長速率隨著鍺含 量而變化。在物理特性方面，矽與矽鍺 p-型選擇性摻雜異質結構用來研 究其傳輸的特性，其結果顯示鍺含量為 0.12 時，其 2DHG 電洞遷移率在 0.65 K 時高達 12500 cm2/V.s，而電洞載子濃度為 3.45 x 1011 cm-2 。同時得到電洞等效質量為0.295 m0 ± 0.01 m0 。而影響電洞遷移率的 主要因子為介面平整度與在矽與矽鍺異質介面之陡峭鍺的含量變化。 同時，在量子井結構中，隨著隔離層厚度(spacer thickness) 減少，則 限制量子井中的電洞濃度增加，而且產生一個局部電場 (local electric field)。同時，由於大的電壓障礙穿透率，使得垂直電導強烈地增加。由 photoluminescence的研究發現，被限制的電洞同時對電子產生一個等效 的量子井。而由於隔離層厚度的效應，我們觀察到shift of band-edge photoluminescence ，此效應是Stark effect ，且是由局部電場影響產 生。 在元件應用方面，利用超高真空化學氣相沉積系統 (UHV/CVD)及 以矽基之製程，製造完成矽與矽鍺 p-型選擇性摻雜場效電晶體。在 5 mm 閘長度 (gate length) 下，extrinsic transconductance gme 為 9.3 mS/mm而 intrinsic transconductance gmi 為 36.3 mS/mm。 我們 成功地製作以正面入射光源藉由 intervalence subband trasnition的p- 型矽與矽鍺量子井遠紅外線光偵測器。在 400 mm x 400 mm 的元件中， 在 77 K 及偏壓Vb = -0.3 V 下，Detectivity D*(4.8 mm) = 2.5 x 108 cm.Hz1/2/Watt, Responsivity R (4.8 mm) = 6.65 mA/Watt。此元件顯 示一個寬的光反應區在 2 至7 mm範圍中，及此矽與矽鍺量子井遠紅外線 光偵測器擁有 high detectivity 與high responsivity，可與 Si ICs 用來製造大面積的光偵測平面陣列。 In this thesis, the growth of Si and strained Si1-xGex alloy epitaxial layer have been investigated by ultrahigh vacuum chemical vapor deposition (UHV/CVD) in the temperature range of 600 - 475℃. The physical properties and devices applications, including p-type MODFETs and p-type QWIPs detectors of the Si/ Si1-xGex quantum well heterostructures have been demonstrated. In the epitaxial layers growth, the deposition of excellent quality Si epitaxy and strained Si1-xGex alloy epitaxial layers, and strained Si/Si1-xGex superlattices have been grown. From the HRXRD measurement of the Si1-xGex alloy layer, the in-wafer deviation of maximum and minimum Ge composition x is 0.2 %, and average uniformity is 0.75 %. The boron concentration of boron- doped Si and Si1-xGexepitaxial layers can achieve 4.0 x 1021 to 1.0 x 1021 cm-3 far beyond the solid solubility of boron in Si and Si1-xGex layers by some times or more orders of magnitude. SIMS measurements demonstrate no Ge segregation at Si/Si1-xGex interfaces grown during 575℃-525℃. The XRR measurement and the HRXRD measurement are used to evaluate the structure parameters of the Si/ Si1-xGex SLS. The interface roughnessesare 0.1 nm for Si and SiGe layers grown at 525 ℃while 0.2 nm grown at 550 ℃ that are obtained by XRR measurement. The Ge compositions x of Si/Si1-xGex SLS are measured from HRXRD and found to increase with layer thickness for the same gas phase composition. A simple model is proposed to explained this phenomena. From this model, the transition region thickness and the transition time can be extracted. The transition regions are in the range from 1.01 nm to 1.46 nm grown at 550 ℃, while from 0.34 nm to 0.66 nm grown at 525 ℃. We conclude that the interface abruptness in UHV/CVD growth is determined by the quantity of surface hydrogen coverage during growth, and the two competing rate-limiting processes could result in a nonmonotonic tread of the growth rate as Ge composition varying during fine-structure growth. The Si/Si1-xGex/Si p-type normal modulation-doped heterostructures are fabricated with an extremely high hole mobility and high sheet carrier concentration, and show a 2DHG hole mobility as high as 12500 cm2/V.s at 0.65 K, at a sheet carrier density ns of 3.45 x 1011 cm-2 for x = 0.12. The study also reveals the hole effective mass m* to be 0.295 m0 ± 0.01m0, which is independent of temperature and magnetic field. The major factors that limit the 2DHG mobility are both the interface roughness and the alloy abruptness at the Si/SiGe heterointerface. The p-type Si1-xGex modulation-doped field effect transistors with a 2DHG SiGe channel are grown by UHV/CVD onto Si substrate to demonstrate the basic compatibility with Si-based technologies. A p-type Si0.72Ge0.28 MODFET with gate length 5 mm, the extrinsic transconductance gme is 9.3 mS/mm and the intrinsic transonductance gmi 36.3 mS/mm. We observed that the decrease of the spacer thickness of QW structures increasethe concentration of holes confined in QW and the local electric field induced. Thus, the perpendicular conductance increases strongly due to a larger tunneling transparency of the potential barriers. The confined holes creates also an effectivequantum well for electrons which was studied by photoluminescence. We observed a shift of the band-edge photoluminescence in dependence on the spacer thickness, which is Stark effect induced by local electric field. We have demonstrated the intervalence subband transition at normal incidence in p-type Si/Si1-xGex QWIP detectors. These 400 x 400 mm2 devices show the detectivitD*(4.8 mm) = 2.5 x 108 cm.Hz1/2/ Watt, the responsivity R(4.8 mm) = 5.65 mA/Watt at bias Vb = -0.3 V at 77 K. The detector show a broad photoreponse at the wavelength range from 2 mm to 7 mm. The Si/Si1-xGex QWIP detectors have very good intrinsic performance, such as high responsivity and high detectivity. So it is expected that these devices have a potential application with Si integrated circuit in fabricating large focal plane arrays.