Abstract
摘要在現階段，多孔矽材料最重要的課題是發展高效率的電激光元件。如果能成功，這將會對 以矽為基材的光電產業產生莫大的助益。時下大部份的研究多著重於p-型多孔矽，此乃因 其光激光效率非常地高。然而，p-型多孔矽本身極高的阻值卻也限制其電激光的效率。相 反的，p+型多孔矽由於其晶粒較大，故擁有極佳的電導特性；但其發光的效率卻也十分地低，甚至無法發光。因此，目前p+型多孔矽應頗適合做為p-型多孔矽元件的電洞注入體， 用以增強其導電能力。更進一步，若未來p+型多孔矽的晶粒大小能被均勻縮小，則其發光 效率亦可能被大幅改善。於是本研究擬檢驗不同晶粒大小的p+型多孔矽的導電特性之變化 ，這對p+型多孔矽於上述兩種電激光元件中的應用是十分重要的。在本論文的第一部份，剖面式電子顯微鏡，孔隙度，及X-ray繞射分析被整合應用於架構p+型多孔矽之立體結構、平均晶粒大小、及及幾何連接方式。同時亦驗證此三種量測方及結 果彼此之間相互吻合。此部份提供了p+型多孔矽一個概略的數量化模型。此模型使得接下 來的電性量測結果能與多孔矽之幾何微細結構相互整合。在第二部份，電性分析結果顯示p+型多孔矽的導電特性主要由其多孔矽骨架表面之空乏區 寬度與其晶粒大小之間的相對關係而決定。文中提出在不同晶粒大小下，導電通路模型的 演進。更進一步，在不同通路環境下對應的傳導機制也被驗證。 實驗結果顯示，本論文中討論的p+型多孔矽具有相當的潛力提供p-型多孔矽元件一良好的電洞注入體。此乃因為p+型多孔矽除了具有良好的導電度之外，同時提供了良好的p+型多 孔矽/矽基材之間的歐姆介面。但在另一方面，本文中的p+型多孔矽尚不適合直接成為電 激光元件之基材。因結果顯示，當其晶粒大小被大幅縮減後，其導電度也隨之大幅下降， 故喪失了原本良好導電度之特性。因此，若要直接應用p+型多孔矽作為發光基材，更高的 摻雜濃度，以及新的p+型多孔矽製備技術用以提供夠小的晶粒，將可能是較佳的選擇。The development of efficient electroluminescence (EL) devicesbased on porous silicon (PS) materials is now a clear targetand, if successful, it is expected to pose great impact onto thesilicon optoelectronics industry. Most of the PS works focus onp- PS because of its superior photoluminescence (PL) efficiencythan that of other PS. However, the extremely high resistivit.躣 p- PS limits its EL efficiency. On the other hand, p+ PS hasmuch higher electrical conductivity but much poorer or even zeroluminescence efficiency than that of p- PS. Therefore, from theprevious description, p+ PS might be a good candidate to serveas hole injectors for p- PS based devices. Furthermore, if onecan homogeneously reduce the Si nanocrystallites' size of p+ PS,the luminescence efficiency of this material might be improved.Thus, the transport behaviors of p+ PS layers with different Sinanocrystallites' sizes are important to examine the potentialsof p+ PS on EL devices.In the first part of this work, XTEM, porosity, and XRDmeasurements were organized to construct a three-dimensionalpicture for p+ PS layers. Both the Si nanocrystallitesinterconnections and the averaged Si nanocrystallites'dimensions of a PS layer were established, and the data revealedfrom these measurements were examined to be consistent with oneanother. Such an approximately quantitative description of p+ PSprovided a foundation for further investigation on theirelectrical behaviors. In the second part, thetransport behaviors in p+ PS samples were determined from therelationship between the width of the depletion layer and thesize of Si nanocrystallites. The dominant conducting channelsevolution in p+ PS samples were proposed and their correspondingtransport mechanisms were verified.The results indicated that the p+ PS layers profoundly studiedin this work should be applicable as the hole injectors for p-PS based devices because of their rather high conductivity andtheir availability for ohmic contact with the metal electrode.On the other hand, the p+ PS layers studied in this work mightnot be very useful as a light emitting PS layers because oftheir conductivity decreasing at smaller dimensions. A possiblelight emitting p+ PS layer should be prepared to have higherdopingconcentration and/or better passivation of the internalpore surfaces. After all, to reduce the size down to theefficient light emitting scale.