利用同步輻射技術為基礎研究飛秒雷射製成硫過量摻雜於矽之次能帶吸收

Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques

李詔永(Chao-Yung Lee)

指導教授 ： 彭維鋒

淡江大學/理學院/物理學系碩士班/碩士(2015年)

https://doi.org/10.6846/TKU.2015.00717

摘要

本論文主要以同步輻射相關實驗研究硫過量摻雜於p-type矽晶產生次能隙吸收與化學態、電子結構、原子結構的相關性。實驗包含光電子能譜(XPS)、X光吸收近邊緣結構(XANES)、X光延伸吸收精細結構(EXAFS)、價電帶放射能譜(VB-PES)以及第一原理理論計算。在S 2p XPS測量，隨著S2-的濃度提高，樣品之次能隙吸收也隨著提高。樣品經過退火處理後，次能隙吸收和S2-濃度同時的減少，而(Sn2-, n> 2)則有所增加，推測次能隙吸收與 S2-濃度有關。在Si的K-edge XANES量測中我們觀察到樣品中矽導帶底端附近之已佔據(未佔據)的電子態密度增加(降低)。而VB-PES測量清楚發現，硫摻雜在能隙中產生雜質態，因此提高次能隙吸收之強度。在第一原理計算態密度泛涵理論(DFT)，預測當硫之濃度大於臨界濃度~0.46％時，造成樣品的Mott 絕緣-金屬相轉變，並且揭示出硫雜質態在價帶最大值與導帶最小值附近增加。

關鍵字

X光吸收近邊緣結構 ； 延伸X光吸收精細結構 ； X光光電子能譜

並列摘要

The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculations. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S2- (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2- species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2-, n> 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in samples. In the calculations by Density Function Theory further predicted the IMT of S-doped Si at a dopant concentration of about 0.46% (~2.3x1020 cm-3) and clearly indicate that the enhancement of the Density of stats at the ECBM and EVBM.

並列關鍵字

black silicon ； XANES ； EXAFS ； XPS ； VB-PES

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