氧化鋅/矽異質結構光偵測器之電性及光性探討

Abstract

隨著科技的進步，人類對地球的過度開發越來越嚴重，能源短缺的問題也被日益重視，可再生的能源議題不斷被拿出來討論，其中太陽能電池是目前最廣泛應用的可再生能源。 雖然GaAs和CIGS的太陽能電池已經可以達到30％以上的效率，但由於的GaAs和CIGS材料成本較高，所以現在在商業上量產的太陽能電池還是以Si為主。至於以Si為主的太陽能電池其效率遲遲無法大幅提升的原因是Si的吸收頻譜與太陽頻譜不吻合，造成能源的浪費和較低的效率。 為了提升太陽能電池的效率，很多太陽能電池會在表面製作奈米結構以降低反射率，然而奈米結構除了可以降低反射率外是否在載子的傳輸有額外的幫助並沒有做詳細的討論。 為了解決Si吸收頻譜與太陽光譜不吻合的問題，我們提出利用寬能隙的材料ZnO和Si結合，達到從紫外光到近紅外光具有寬廣且平坦吸收頻譜的光偵測器，其光響應在負偏壓3V的條件下達到0.17A/W，接著利用我們奈米小球的鋪排，使其光響應在可見光範圍(400nm~650nm)提升17.6％。 最後為了探討載子傳輸對光響應的影響，我們結合了GZO、a-Si、Si以及奈米小球蝕刻技術在元件中材料的接面上製作奈米結構，發現奈米結構除了可以有效的降低反射率，確實對載子的傳輸有幫助，較快的載子傳輸可以使載子更有效率的到達電極，進而大幅提升元件的光響應。 總結以上的實驗成果，不同能隙材料的異質結合，再利用簡單奈米小球鋪排技術及奈米元件的製作，相信可以有很大的潛力應用在製作高效率太陽能電池方面。

By the advance of technology, the overdevelopment of the Earth by human beings is more and more serious and the energy issue is attracted more attentions. However, photovoltaics are the more applicable renewable energy now. In spite of the GaAs and CIGS based solar cells could have the high conversion efficiency more than 30%. The major commercial solar cells are still focused on Si based solar cells due to the high material cost of GaAs and CIGS solar cells. The major key issue on high conversion efficiency solar cell manufacturing is the mismatch of absorption spectrum between crystalline Si and solar spectrum. However, this mismatch of absorption spectrum will result in the energy loss and low conversion efficiency. In order to manufacture the high conversion efficiency solar cells, sub-wavelength textured surface and nanostructure devices were fabricated to reduce the surface reflectivity which could result in more light trapped by device structure. Nevertheless, it’s few to discuss that nanostructure device not only reduce the surface reflectivity but also probably help the carriers effectively transport to the contact electrodes. We utilized the ZnO and Si semiconductor materials to fabricate heterojunction photodiodes with flat and broad absorption band spectrum. The responsivity of photodiodes is 0.17A/W under -3 volts bias. By above approach, it’s possible to solve the mismatch issue of absorption spectrum between crystalline Si and solar spectrum. V By the technique of nanosphere spraying on the top of device surface, 17.6% enhancement of responsivity was achieved between 400nm to 650nm. Following, we combine GZO, i a-Si and p+-Si and the technique of nanosphere lithography to fabricate the nanopatterned n-GZO/i a-Si/p+-Si heterojunction photodiodes. We observed that nanostructure on devices not just only reduce the surface reflectivity but also help carriers effectively transport to the contact electrodes due to the shorter transit paths in nanostructure devices. However, we observed shortest transit time and highest responsivity in n-GZO/i a-Si/nanopatterned p+-Si heterojunction photodiodes. To summary above results, it has the infinite potential applications to solar cells by fabricating devices with the combination of materials possessing different energy band gap, simple nanosphere lithography and the achievement of nanostructure device manufacturing.