本論文將對(0001)面藍寶石(sapphire, Al2O3)基板成長氮化銦鎵(InGaN)太陽能電池作一系列的材料分析與元件特性探討，其中包含分別利用塊材(bulk)、超晶格(superlattice)與多重量子井(multiple quantum well, MQW)等設計做為正型/未摻雜/負型接面(p-i-n junction)型式電池結構的吸收層。
由於高銦含量與較厚的塊材結構在晶格不匹配(lattice-mismatched)的藍寶石基板上將導致大量的晶體缺陷而無法產生光伏(photovoltaic, PV)效應，為了改善磊晶品質，我們成功利用藍光波段的短週期InGaN/GaN超晶格主動層來吸收太陽光；隨後，我們在超晶格結構中的位障(barrier)層加入適當含量的鋁(AlN)，利用極化(自發&壓電)現象所導致的電荷來提高InGaN太陽能電池的內建電場，如此可減少主動層中光載子被高密度缺陷所散射或復合的機率，因而提升元件效率。我們更進一步將InGaN電池結構成長於圖形化藍寶石基板(patterned sapphire substrate, PSS)之上，InGaN電池元件除了漏電流大幅降低之外，對於PV系統在戶外操作時不同太陽角度的投影損失亦較傳統平面式藍寶石基板所成長的電池元件要來得少，如此可望降低電池實際發電成本。我們亦探討InGaN太陽能電池在高聚光條件下的光電特性，吸收層為InGaN/GaN MQW的電池元件在100倍太陽光(AM1.5G頻譜)強度之下，其開路電壓與填充因子分別高達2.49 V與0.71，其光電轉換效率為2.23%。
最後我們探討串聯電阻對InGaN電池元件的影響，在不損壞半導體磊晶品質的前提之下，我們加入適當含量與厚度的AlGaN或InGaN磊晶層，由於元件中載子的側向導電率上升因而可降低元件的串聯電阻；利用雷射剝離(laser lift-off)法，我們成功將InGaN太陽能電池從絕緣的藍寶石基板轉置到導電率佳的矽基板之上，如此光載子從主動層傳導到外部電路的傳輸距離大為縮短至僅數個微米，使得串聯電阻大幅減少49%，光電流增加72%，因而大幅提升InGaN電池元件的光電轉換效率。

In this dissertation, the p-i-n type InGaN/sapphire-based photovoltaics (PV) were epitaxially grown on (0001) sapphire substrates by the metal-organic vapor phase epitaxy reactor. The InGaN PV devices with several absorption layer designs, including the bulk InGaN layer, the short-period InGaN/(Al)GaN superlattice and the InGaN/GaN multiple quantum well (MQW) structures, were fabricated and characterized.
First, PV devices with an In0.25Ga0.75N/GaN superlattice absorption layer were demonstrated to have better solar response compared to those with a 200-nm-thick single In0.25Ga0.75N layer. The superlattice structure maintained better material qualities with high indium contents and thick absorption layers. Afterward, we proposed the other InGaN PV device with an Al0.14Ga0.86N/In0.21Ga0.79N superlattice structure. The polarization-induced charges at the hetero-interfaces caused enhanced built-in electric fields in the active layer, preventing photogenerated carriers from scattering or recombining by the charge-related defect states in InGaN/sapphire crystals. To improve material qualities, the patterned sapphire substrates (PSSs) were applied. The PSS-grown InGaN PV cells exhibited not only reduced leakage current but also reduced projection loss from obliquely incident sunshine. At concentrated 100-sun conditions with the AM1.5G spectral irradiance, the PSS-grown InGaN/GaN MQW PV cells exhibited high VOC (2.49 V) and FF (0.71), corresponding to a PCE of 2.23%. Finally, the series resistance effects were also studied, including additional AlGaN and InGaN insertion layers that were to enhance the lateral conductivity of photocarriers. In addition, InGaN/sapphire-based PV cells that were bonded onto conducting wafer carriers exhibited much reduced series resistance, which was attributed to the shortened carrier transit length (from hundreds to several micrometers) between active layers and external circuits, preventing photogenerated carriers from being scattered or recombined in high threading dislocation density epitaxial layers.

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