在本論文中,我們藉由適當的改變實驗參數,並利用不同型態的矽基板作蝕刻,進而得到各種孔隙大小多孔矽薄膜。其中,我們發現藉由具有P-N junction 的矽基板能有效的改善N型層較難蝕刻的情形;且P-N type中P-type layer的厚度對蝕刻的結果亦有影響。並利用P-L及FTIR光譜來推論,產生多孔矽光激發光的原因是由於Si-O-Si的鍵結產生SiOx的螢光物質,導致多孔矽產生光激發光。而在P-L光譜中發現,蝕刻N-sub on P-epi silicon所得的多孔矽具有較好的光激發光現象,除了有較大的強度外,其發光峰值也有藍移的現象。
在實驗中我們還發現藉由特殊的參數控制,可以獲得一些比較特別的孔洞結構,例如利用電場的變化產生磁場而獲得的發散狀孔洞,及在一個長時間的蝕刻下而獲得的多孔矽側向蝕刻結構。
此外我們在以時間為參數的探討中發現,在照光環境下,多孔矽蝕刻反應會有照光極限的產生,且其孔隙率隨蝕刻時間增長亦會跟的增加,並且從FTIR光譜中發現其不同時間下的多孔矽鍵結變化。
針對多孔矽的電性分析,可以發現多孔矽的電阻值會隨孔隙率上升而增高,但其電阻會因表面的macro porous的擴大,造成濺鍍正面電極時,金屬有效的沉積在表面孔洞內,使得其部份介面電阻降低,且在n-epi on p-sub多孔矽上則可以發現明顯電阻的負微分現象。
In this study, the porous silicon (PS) films are fabricated by electrochemical anodization method. Various experimental parameters, such as etching current density, etching time and HF concentration, are investigated. Photoluminescence (PL), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) mapping and Fourier transform infrared spectroscopy (FTIR) are used to analyze the film characteristics in the PS. N-type PS is difficult to form by conventional method for the lack of holes. However, with the forward biased P-N junction, sufficient holes can drift from P layer to N layer and hence the N-type PS can be easily formed. In addition, the thickness of P-type layer influences the etching result. From P-L spectrum, it can be found that etching on the N/P sample produces better PL emission and blue-shifting. Deep and straight shape pores can be obtained. The morphology, cross section view, porosity, PL and EDX analysis are investigated and compared with conventional method.