微結構的矽基板光二極體

Abstract

受光元件主要可分成光偵測器和太陽能電池兩類。高效率的受光元件有電子電洞對的高產生率和低複合率。藉由把元件表面粗糙化，可以造成入射光在元件表面多次反射，使光被吸收的機會增加，還能增加pn接面的面積，所以能夠提高電子電洞對的產生率，使得元件的效率提升。本實驗是使用濕蝕刻的方式，用氫氟酸和硝酸銀的水溶液在ｐ型的單晶矽表面蝕刻出一片一維結構的矽奈米線來達到將元件表面粗糙化的目的。 元件的製作方式十分簡單，在經過微結構處理矽基板上鍍上一層非常薄的參雜氫的本質非晶矽(a-Si:H)，這是用來鈍化蝕刻對矽基板造成的表面缺陷，使光電流較容易導出，然後再在基板上鋪上一層氧化鋅的溶液，使溶液滲入矽的奈米線之間，形成一層n-ZnO薄膜。最後將樣品放入氮氣的環境中退火，使氧化鋅結晶品質變好，形成第二類的異質接面(n-ZnO/ a-Si:H/ p-SiNW)。這類的PIN半導體元件對紫外光較為敏感，且有高光反應和低電流雜訊，這些特性使得n-ZnO/ a-Si:H/ p-SiNW元件在光的檢測上有不錯的表現，所以可以用在火焰偵測和飛彈煙幕偵測等方面。 由光電轉換效率的量測結果發現，在低的逆向電壓時，經過微結構處理的元件比未經處理過的元件對光來的敏感，光電流也較大。但是如果中間不加上有鈍化效果的a-Si:H，經過微結構處理的元件(n-ZnO/ p-SiNW)的光電流會很小，這是因為矽表面的缺陷把電子電洞抓住了，使光電流很難導的出來。所以提高鈍化SiNW的效果及n-ZnO的結晶品質，是接下來重要的課題。

Photodiodes and solar cells are both photo-sensitive devices. They are devices that can absorb light power and change it into the electrical signal. High-efficiency photo-sensitive devices can easily generate a large amount of light electron-hole pairs which hardly recombine. Since electroless wet-etched SiNWs have rough surfaces, they offer excellent opportunities for improving the quantum efficiency of a photo-sensitive device since nanostructures can facilitate light absorption and radial collection of photo-generated carriers, thus giving rise to high efficiency. Our fabrication process is very simple and low cost, which is very useful for practical application. After SiNW growth, a very thin a-Si:H layer was grown on SiNW by PECVD for passivation., and the thin film of ZnO was grown on a-Si:H by sol-gel methods. Then the p-SiNW/a-Si:H/n-ZnO were annealed in a furnace at different temperatures 500 °C for 0.5 hour to improve ZnO crystalline quality. The device provides an excellent alterative for detecting light. To reduce the effect of SiNWs' surface defects, one of the possible ways is to insert an additional a-Si:H layer between ZnO and p-Si nanowires. The additional a-Si:H layer passivates the interface defects due to the presence of atom hydrogen during the deposition. The IPCE result points out that the light current of the p-SiNW/a-Si:H/n-ZnO photodiode shows a significant increase compared with that of p-SiNW/n-ZnO photodiode under small reverse voltage. It indicates that the a-Si:H can effectively passivate the interface defects and play an important rule.