摘要
本論文中，探討單晶矽太陽能電池發光和少數載子生命週期，以及鍺np接面發光元件在直接能隙發光的增強方法。 太陽能電池能夠以發光及載子生命週期來判測其元件的好壞。在電發光方面，使用電子-電洞-電漿複合模型得到理論線。在瞬時性電激發光量測，使用三種複合機制來得到理論線，分別是放光複合、SRH複合以及歐傑複合，於是能夠得到此元件少數載子生命週期大約是 1.8毫秒。 在室溫下發現鍺元件不論在光激發光或是電激發光的頻譜，在1.6微米公尺處都可以看到直接能隙發光的現象。此處提到有幾個方法能夠增加鍺元件在直接能隙放光的強度：(1)增強電流密度使電子更集中在直接能隙區域,(2)升高溫度增加高能電子在直接能隙的分佈,(3)外加雙軸張應力會拉近直接能隙與非直接能隙的距離，造成累積在直接能隙的電子變多。這些方法都能夠增強鍺元件在直接能隙發光。由於直接能隙的發光複合係數遠比非直接能隙來得大，因此若增強直接能隙發光，則能夠增加鍺元件的發光效率。
並列摘要
In this thesis, the emission and minority carrier lifetime of monocrystalline Si solar cell and enhancement of direct bandgap transition from Ge np junction LED are discussed. The emission image and lifetime measurement is very useful as a diagnosis tool for solar cells. The infrared emission at the Si band edge is observed from an n+p solar cell and is confirmed by the electron-hole plasma recombination model. The temporal electroluminescence is measured and fitted with the radiative, SRH and Auger recombination mechanisms. The minority carrier lifetime of the value ~1.8 ms is measured. The direct bandgap transition (1.6um) from Ge was observed in the photoluminescence (PL) and electroluminescence (EL) at room temperature. The methods to enhance direct radiative recombination are: (1) electron injection into direct valley by increasing current injection level at forward voltage, (2) increasing device temperature to increase electron population in direct band, (3) using tensile strain to move the direct valley closer to indirect valleys. The direct bandgap transition from Ge can further increase the emission intensity due to higher radiative recombination coefficient as compared to indirect bandgap transition.
參考文獻
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