飛秒脈衝雷射製備銅銦鎵硒薄膜之超快載子動力學研究

Abstract

本論文利用脈衝寬度分別為奈秒及飛秒之雷射源，以脈衝雷射蒸鍍法製備銅銦鎵硒薄膜。為比較兩種不同製程製備之薄膜品質，我們藉由X-ray繞射儀(XRD)及拉曼光譜儀(RS)比較薄膜之晶格結構，以掃描式電子顯微鏡比較其晶粒大小，最後以光激發－探測系統量測其超快載子動力學行為。從XRD圖發現， fs PLD 薄膜其I(220/204)/I(112)大小為1/10，較ns PLD薄膜I(220/204)/I(112)強度比(~1/100)大上許多，而其他軸向之特徵peak強度也明顯增加，顯示其黃銅礦結構較ns PLD薄膜佳；從RS圖也發現，fs PLD之薄膜，其A1 mode強度較 ns PLD薄膜A1 mode強度強，顯示其結晶性較佳；而樣品之超快載子動力學亦觀察到，fs PLD薄膜其缺陷相關非輻射復合率較低，亦暗示其元件有較好的光電轉換效率。

We prepared CIGS thin films by pulsed laser deposition(PLD), the pulsewidth of the laser sources are nanosecond and femtosecond, respectively. We analyzed their crystal structure utilizing X-ray diffraction(XRD), and Raman spectroscopy(RS). Following, we compared their grain morphologies by scanning electron microscopy (SEM) images. Finally, the ultrafast carrier dynamics measured by optical pump-optical probe system(OPOP). By XRD patterns, we found the ratio I(220)/(204) /I (112) are ~1/10 and ~1/100 in fs PLD CIGS and ns PLD CIGS, respectively. Other peaks also enhanced apparently in fs PLD CIGS. The results of RS measurement showed the A1 mode is stronger in fs PLD CIGS than ns PLD CIGS. It all reveal the better chalcopyprite structure in fs PLD CIGS. Lastly, ultrafast carrier dynamics in CIGS thin films are investigated by using OPOP spectroscopy. And we obtained lower defect-related non-radiative recombination rate in fs PLD CIGS, reflecting a better quality with higher energy conversion efficiency of them.