內嵌絕緣層矽金氧半場效電晶體與銅銦鎵硒太陽能電池之鈍化及均勻度分析

Insulating Halo NMOSFET and CIGS Solar Cells

許文瑋(Wen-Wei Hsu)

指導教授 ： 劉致為

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.10735

摘要

在本篇論文中，提出了一種新型的內嵌絕緣層矽金氧半場效電晶體。透過此種內嵌絕緣層矽金氧半場效電晶體，短通道效應可以明顯的改善。嵌入之二氧化矽/氮化矽 絕緣層於環型佈植區(HALO)，環型佈植之濃度會因此被阻檔而增加，進而改善短通道效應。如果佈植的濃度調淡，使得內嵌絕緣層矽金氧半場效電晶體之關電流調整至近似控制元件，將使元件的通道濃度變低，元件將因為較低的垂直電場而有較高的載子遷移率。此外，內嵌絕緣層矽金氧半場效電晶體還可以阻檔STI產生之壓應力，所以N型場效電晶體之載子遷移率將可以再提升。元件的表現可以透過模擬來最佳化內嵌絕緣層之位置。實際製程之元件量測結果，最高可以有23%之開電流之增加。此外，量測結果亦有7%接面電容之減少及8%的環形振盪器速率之增加(只有N型場效電晶體應用內嵌絕緣層之技術)。最後，元件的可靠度亦仔細的量測檢視，內嵌絕緣層矽金氧半場效電晶體並不會使可靠度有明顯之減少。
在論文的第二部分，銅銦鎵硒太陽能電池是主要的研究內容。氧化鋁可以用來鈍化銅銦鎵硒薄膜的表面。因為表面複合速率之減少光激發光的量測可以觀測到100倍的光強。而且光激發光的強度會隨著氧化鋁之厚度從5nm增加到50nm而增加。透過電容量測之驗證，氧化鋁薄膜中帶有負固定電荷。最後，我們用第一原理之模擬可以發現氧化鋁可以使得銅銦鎵硒薄膜界面缺陷密度有35%之減少。此等級之減少沒有辦法完全解釋表面複合速率之減少，因此固定電荷之電場效應才是氧化鋁能夠有良好鈍化銅銦鎵硒表面之主因。
接下來，度過模擬來分析銅銦鎵硒太陽能電池之薄膜均勻度如何影響電池之效率。同時考慮了不均勻可能會發生在電池本身，或是在不同模組之間。在模擬中，選定三種參數，分別為生命週期、載子濃度及鎵的比例來做不均勻之分析。研究中指出，鎵的比例之不均勻是影響最後效率之最重要的因子。因為當鎵的比例改變時，開路電壓及短路電流皆會有一定程度之改變，而開路電壓會不均勻之薄膜中最差的一部份而決定。研究亦指出，模組受到不均勻的影響將比電池所受到的而大，其主因是因為其較差之填充因子。
附件A：鍺之直接能隙較大，其也較容易受到再吸收，直接能隙之發光強度將隨著不同元件之發光深度而改變。垂直電流之電激發光元件，因為電場之幫助，其載子之分佈比光激發光來得深。因此其直接能隙之發光強相對的低。水平電流之元件可以幫助載子之分佈較接近表面，因此可以有相對強之直接能隙之發光。
關鍵字：內嵌絕緣層/金氧半場效電晶體/壓應力/銅銦鎵硒太陽能電池/氧化鋁/均勻度

關鍵字

內嵌絕緣層 ； 場效電晶體 ； 壓應力 ； 銅銦鎵硒太陽電池 ； 氧化鋁 ； 不勻均

並列摘要

In the first part of this dissertation, IH MOSFET is investigated. Short-channel controllability by insulating halo (IH) is investigated using the NFET strained-Si technology. By embedding SiO2/Si3N4 insulators in the halo regions, the increase of halo implant concentration reduces the S/D depths, and improves short channel effects such as drain induced barrier lowering. With Ioff similar to the control device at the same gate length by adjusting the threshold voltage, the channel doping can be reduced, and the channel mobility increases due to the decrease of vertical electric field. Moreover, insulating halos reduce the STI compressive stress in the channel and yield high electron mobility enhancement. The device performance is optimized based on simulation design. Up to 23% Ion improvement was experimentally achieved by optimal insulating halo insertion. 7% lower junction capacitance and 8% ring oscillator speed improvement is demonstrated when IH is adopted in NFET alone. Moreover, device reliability is carefully examined and is not adversely impacted by IH insertion.
In the second part of this dissertation, CIGS solar cell is investigated. With Al2O3 passivation on the surface of Cu(In,Ga)Se2, the integrated photoluminescence intensity can achieve two order of magnitude enhancement due to the reduction of surface recombination velocity. The Photoluminescence intensity increases with increasing Al2O3 thickness from 5nm to 50nm. The capacitance-voltage measurement indicates negative fixed charges in the film. Based on the first principles calculations, the deposition of Al2O3 can only reduce about 35% of interface defect density as compared to the unpassivated Cu(In,Ga)Se2. Therefore, the passivation effect is mainly caused by field effect where the surface carrier concentration is reduced by Coulomb repulsion.
Next, how film inhomogeneity would affect the CIGS solar cell performance is investigated. Inhomogeneity taken places both within a cell and between cells (module) are considered. The variations of lifetime, doping concentration, and Ga fraction of CIGS cells and modules are investigated by simulation. Ga fraction variation is found to have a significant impact on cell performance, where else lifetime and doping concentration variation on cell performance is mild. The Ga variation causes the open circuit voltage (Voc) variation across a single cell, and the smallest Voc dominated the net Voc. The module efficiency is degraded more significant by the Ga variation than cell due to the additional degradation of the fill factor.
Appendix A: Since the direct bandgap emission of Germanium (Ge) has a higher energy than the fundamental bandgap and its reabsorption nature, the emission intensity of direct bandgap depends on the depth where emission occurrs. For vertical current flow, the carrier profile in electroluminescence distributes deeper than in photoluminescence due to electric field, and leads to relatively weaker direct bandgap emission. A lateral current flow can confine carrier distribution near the surface thus relatively stronger direct bandgap emission is observed.

並列關鍵字

Embedded Insulator ； MOSFET ； Compressive stress ； CIGS solar cell ； Al2O3 ； Inhomogeneity

參考文獻

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[3]. M. Powalla and B. Dimmler, “Scaling up issues of CIGS solar cells,” Thin Solid Films, 361, 540 (2000).

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