應用非晶矽鍺薄膜技術於光伏及光偵測器之開發

Abstract

本論文之研究是利用超高頻率化學氣相沉積系統進行製備氫化非晶矽鍺薄膜光電元件，使用矽鍺薄膜的目的是因為非晶矽在長波長(750nm以上)無法進行有效的吸收，而為了更有效率的使用太陽光頻譜，因此在矽基薄膜中參雜鍺元素，進而使光吸收層之能隙得已下降。經由不同參數調變下，能隙的範圍可由1.7eV到1.45eV。本文中所展示之氫化非晶矽鍺薄膜的光能隙為1.55eV。利用此吸收層製成之氫化非晶矽鍺單接面太陽能電池其轉換效率可達4.65%，其頻譜吸收範圍為300~850nm。為了使氫化非晶矽鍺薄膜的缺陷密度降低，在製程上我們選用乙矽烷與鍺烷為前驅物進行元件的製作，因為兩者的沉積速率相近，而非選擇矽烷。低缺陷密度的光電元件因為照光後所產生的電子電洞對較容易被萃取出，故短路電流密度、轉換效率與量子效率得以上升。 在本文中我們也增加了氫化非晶矽鍺光吸收層的厚度，其目的為使長波長的量子效率提升，當厚度達到1μm後，在波長為750nm以上之量子效率有明顯的提升，使得此光電元件也可應用於光檢測器上。 未來的研究方向將致力於利用此氫化非晶矽鍺薄膜與先前開發出來的高效率非晶矽太陽能電池做結合，形成堆疊型a-Si/a-SiGe之高轉換效率與高光譜吸收率的太陽能電池。

In this thesis, we investigate the performance of hydrogenated amorphous silicon germanium thin film which can be used in photovoltaics and photod-etectors fabricated by very high frequency plasma enhance chemical vapor deposition system. In order to utilize the solar spectra in near infrared regime and obtain higher quantum efficiency, but amorphous silicon thin film cannot efficiently absorb the solar spectra regime beyond 750nm since the optical band gap of amorphous silicon is about 1.8eV to 1.9eV. So we decided to dope germanium atom into silicon thin film to form amorphous silicon germanium, whose band gap can lower to 1.45eV （1.45eV~1.7eV）. In this article, we used the optical band gap about 1.55eV a-SiGe:H film to fabricate photovoltaics, whose conversion efficiency can reach 4.65% and the absorbing spectra of quantum efficiency can be broadened from 300~850nm.For the purpose of lowering the defect in the a-SiGe:H thin film, we chose disilane and germane as precursor rather silane and germane, since the components of the first combination（disilane and germanium）have similar deposition rate. The benefit of low defect a-SiGe:H thin film is easily extracting the electron-hole pairs after light exposure, causing higher short-circuit current density、conversion efficiency and quantum efficiency。 We also increase the photovoltaics’ thickness of absorption layer to obtain higher quantum efficiency at the near infrared regime。When the thickness goes up to 1μm，we can observe that the wavelength beyond 750 will raise obviously. So we can also use this component with proper absorption layer thickness as photo-detector. In the future, our research will focus on using hydrogenated amorphous silicon and silicon germanium thin film to fabricate a-Si/a-SiGe tandem photovolaics with high conversion efficiency and broad band quantum efficiency