利用飛秒脈衝雷射提升銅銦鎵硒薄膜效率之研究

Abstract

本論文利用不同脈衝寬度的雷射源(分別為奈秒與飛秒)來沉積銅銦鎵硒(CIGS)薄膜於不同溫度的基板上。為了找到沉積薄膜的最佳條件，我們利用X光繞射儀(XRD)來探討薄膜結晶品質，並以掃描式電子顯微鏡來判斷其表面形貌與厚度，最後利用能量散佈光譜儀(EDS)來探討薄膜的組成成分，從以上這些結果中可以發現在基板溫度為500℃時薄膜具有最好的結晶品質。另外我們利用飛秒脈衝雷射退火銅銦鎵硒非真空製程薄膜，從XRD頻譜圖發現薄膜黃銅礦結構的優選軸向(112)得到了明顯的增強以及改善，確定了薄膜藉由退火後結晶品質的改善。在光學性質方面，利用光激發螢光光譜量測薄膜施體能階與受體能階間的變化，發現光譜有紅移的現象，而我們利用改變激發光能量的分析發現這個現象可以歸因於他是屬於典型的施體受體對(DAP)躍遷機制，因此我們量測變溫的光激發螢光光譜並做分析討論，發現施體的活化能從原來的為12.58 meV提升到14.95 meV，這代表著退火後施體雜質濃度下降。接著在利用超快載子動力學去分析發現退火後缺陷相關非輻射復合率較未退火前來的低。最後我們將它做成元件後討論退火前後電性的變化，我們發現退火後開路電壓、短路電流以及填充因子都得到了有效的改善，也間接地將我們元件轉換效率提升。

In this study, CuIn1-xGaxSe2 (CIGS) thin films were prepared by nanosecond (ns)- and femtosecond (fs)-pulsed laser deposition (PLD). Then, We used X-ray diffraction to investigate the crystallization characteristics, because we want to find the best substrate temperature to growth CIGS thin film. In SEM images, we compared the crystal morphology. From the EDS, we confirm that when the substrate temperature is 500℃, the CIGS thin films has more homogenous elemental distribution. From the above results , the best crystalline quality of the thin film occurred at the growth temperature of 500℃. Then, we have successfully demonstrated the advantages of femtosecond laser annealing on non-vacuum CIGS thin films. The femtosecond laser annealing can induce the re-crystalline without melting effect. The XRD pattern has suggested the (112)-orientation of thin films was significantly improved. And the PL spectrum implied some defect-level or band-fluctuation were eliminated so that the smaller FWHM of PL peaks and higher saturation power were observed in annealed CIGS thin film. From femtosecond pump-probe spectroscopy, we can observed that surface recombination is suppressed by laser annealing. Finally, the improvements of performance in the devices consist with the result of XRD and PL measurement. The conversion efficiency and ideal factor were obviously enhanced after laser annealing. This result has revealed femtosecond laser annealing is a promising approach to rapidly improve the CIGS thin films prepared by non-vacuum particle synthesis.