硒化鎘微晶玻璃薄膜之製備與光學性質研究

Abstract

本實驗以射頻濺鍍法製備可應用在紅光雷射的CdSe-SiO2微晶玻璃光開關（Optical Switching）薄膜。濺鍍靶材的準備分成溶凝膠法與貼靶法，實驗過程中發現貼靶法能以高功率進行濺鍍，製程穩定、方便,是較佳的微晶玻璃製作方式。以紫外-可見光譜儀(UV-Visible Spectroscopy)與光致螢光光譜儀（Photoluminescence Spectroscopy, PL）量測其線性光學性質並估計能隙大小，結果顯示影響射頻濺鍍所製備出來的微晶玻璃薄膜微晶大小之主要因素為摻雜濃度 ; 濺鍍功率的影響則很小。電子微探儀（Electron Probe X-ray Micro-analyzer，EPMA）成分分析發現貼靶法能製備出CdSe含量高達87 wt%的半導體微晶玻璃。電子顯微鏡（Transmittance Electron Microscopy，TEM）分析證明用射頻濺鍍法可以在不加熱基板的低溫條件下製備出結晶性良好的CdSe微晶玻璃薄膜，分析微晶粒徑發現CdSe微晶的尺寸確實隨著CdSe含量增加而變大，與PL量測的能隙大小結果相比較，其符合量子侷限效應理論的預測。Z-scan量測發現能隙小於雷射光子能量的微晶玻璃呈現相當大的非線性吸收效應， 1 μm厚的CdSe微晶玻璃薄膜可獲得的的穿透率變化最高達到43%，且穿透率變化量而量隨光強度與脈衝重複率增加而增大，綜合吸收係數、能隙大小與Z-scan的量測結果判斷，本實驗觀察到的非線性吸收的機構應為熱效應。

In this experiment , RF-sputtering deposition method was applied to prepare CdSe-doped glass thin film which can be used as the optical switching of red laser. there are two ways to prepare sputtering targets :one is to utilize sol-gel process; another is to put CdSe chips on SiO2 target (chips-on-target method). Chips-on-target method allows both the high-power sputtering and stable process possible and has much convenience. It is preferred as the better way to prepare semiconductor doped glass (SDG) thin film. UV-Visible Spectroscopy and Photoluminescence Spectroscopy (PL) are used to measure the linear optical properties and to estimate the band gap. The results showed that the primary factor affecting the size of the micro-crystals is the concentration of CdSe, whereas the effect due to sputtering power is small. As revealed by the electron Probe X-ray Micro-analyzer (EPMA), the composition in samples prepared by chips-on-target method possesses pretty high amount of CdSe up to 87%. The CdSe-doped glass thin film with fine crystallinity prepared by RF-sputteing at low temperature without heating substrates has been proved by TEM analysis. By analyzing the size of the microcrystals, the size of microcrystals grows as the amount of CdSe increases. Both the analysis of crystalline size and energy gap by PL correspond to the anticipation of the quantum- confinement theory. Z-scan measurement showed that the micro-crystalline glass thin film with the band gap less than that of the laser photon energy provides huge nonlinear absorption effects. The thin film with the thickness of 1 μm reveals that the transmittance change increases as the light intensity and repeating rate increase and the biggest change can be up to 43%. By incorporating all the analyses of absorption coefficient, band gap and Z-scan measurement, the mechanism of this nonlinear absorption effect observed in this experiment is identified as thermal effect.