載子在伸張應變型鍺量子點陣列中直接能隙轉換之研究

本論文利用感應耦合SF6/C4F8電漿蝕刻定義矽鍺串珠柱狀陣列之後，再佐以選擇性高溫氧化將矽鍺串珠柱狀陣列轉換成鍺奈米晶粒簇團/二氧化矽柱狀陣列。利用氮化矽間壁層得以促進鍺奈米晶粒簇團有效聚集的特性，在900℃ 高溫熱回火環境下，進一步將鍺奈米晶粒簇團聚集成鍺量子點。在此高溫氧化過程中，鍺會不斷與二氧化矽鍵結並因氧化層的體積膨脹而向外拉扯，導致最後形成的鍺量子點會感受到伸張式的應力。根據拉曼光譜分析其伸張應力約為 0.4~1.6%，有助於鍺量子點內的載子得以經由直接能隙複合發光。因此，本文開發製備出鍺量子點碟型共振腔結構，以增強鍺量子點發光的強度並探討其光學特性。透過光激發螢光譜線可得知受到伸張應力影響的鍺量子點之光激發峰值約在 0.83 eV，趨近於鍺材料中導電帶的Γ valleys 到價電帶的能量差，證明其確實具有直接能隙傳輸複合的可能性。另外根據強度相依的光激發螢光量測譜線可得到α 趨近於1，表示光訊號是來自於導/價電帶中激子複合而成，而透過溫度相依光激發螢光譜線量測可得知鍺量子點的活化能約為 10~17 meV，此外亦透過時間解析光激發螢光量測鍺量子點的載子複合時間約為 4.7 ns。本文呈現利用伸張應力改變鍺量子點的能隙，其峰值 0.83 eV對應其發光波長約為 1500 nm 可有效應用於現今近紅外光通訊波段。經由掃描式電容-電壓特性曲線，亦可以觀察到在980 nm的光照射下，有明顯的滯留迴路特性，再次驗證伸張式形變之鍺量子點陣列具有直接能隙吸光之能力。

關鍵字

鍺量子點；直接能隙傳輸

並列摘要

In this thesis, we formed abacus-bead SiGe pillar array by using SF6/C4F8 Inductively Coupled Plasma etching, and followed by selectivity oxidation transforming the abacus-bead SiGe pillar array into Ge nanocrystallites/SiO2 ¬pillar array. With the help of Si3N4 sidewall layer on movement and segregation of Ge nanocrystallites, germanium quantum dots (Ge QDs) were fabricated at 900℃ thermal annealing. During high-temperature oxidation, germanium would bond with as-formed SiO2 continuously and then be pulled outwards because of volume expanding of SiO2, leading to the tensile strain state in Ge QDs. Raman Spectroscopy measurement confirmed that the tensile strain in Ge QDs was about 0.4~1.6%, leading to a quasi-direct bandgap transition properties of Ge QDs. Therefore, we developed a Microdisk cavity for fabricated Ge QDs to enhance Ge-QD luminousness and explored its optical properties. The corresponding photoluminescence (PL) peak of Ge-QD Microdisk centered at 0.83eV, which corresponded to the energy difference from Γ valleys to valance band in germanium, demonstrating the probability of direct-transition recombination for Ge QDs. Besides, a fitted α approaching to 1 in the power-dependent PL spectra suggested that PL emission was being dominated by exciton recombination in the Ge QDs and furthermore, the activation energy (Ea) extracted from temperature- dependent PL was about 10~17 meV. Time-resolved photoluminescence show the carrier lifetime of ~ 4.7 ns. This study demonstrated the modification of Ge QDs bandgap by tensile strain, and its peak energy located at 0.83 eV, corresponding to wavelength 1500 nm, showed the promising potential for applications in near infra-red (NIR) communication. In capacitance-voltage (C-V) characterization, significant hysteresis curve under a 980 nm laser illumination double confirmed that tensile strained Ge QDs with quasi direct-bandgap possess the ability of light absorption.

並列關鍵字

Ge quantum dot ； Direct-bandgap transist

參考文獻

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載子在伸張應變型鍺量子點陣列中直接能隙轉換之研究

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