硒化鎵薄膜產生兆赫輻射之研究

Abstract

本論文利用PLD鍍膜系統成功製備(001)GaSe薄膜，系統化地找出最佳鍍膜條件。這些不同鍍膜條件的薄膜藉由X-ray繞射分析來確認薄膜的結構，並利用拉曼光譜分析進一步檢驗薄膜成份。薄膜表面平整度經由原子力顯微鏡量測而得。最後利用霍爾效應量測薄膜的載子濃度和用傅立葉轉換紅外線光譜儀確認薄膜在遠紅外光區的穿透率。 之後透過兆赫輻射時域頻譜量測分析技術，研究不同鍍膜條件薄膜的兆赫輻射產生效率，並與單晶做比較及討論。接著從兆赫輻射的產生機制上來比較GaSe單晶在激發光為800 nm與400 nm下的差異性，以及單晶與薄膜間的差異性。最後藉由檢測各種機制的特性，提出薄膜可能的產生機制是光整流效應與光激載子混合。

GaSe thin film is successfully prepared by pulsed laser deposition and the best deposition conditions are confirmed by systematic analysis. The crystal structure and composition of as-prepared thin films under different deposition conditions are examined by X-ray diffraction and Raman spectrum, respectively. The carrier concentration of thin films is evaluated by Hall-effect measurement and the transmittance in far-infrared range is measured by FTIR method. In the second part of this thesis, the efficiency of THz radiation generated by thin films of different deposition conditions are compared with GaSe single crystal. Finally, by measuring the characteristics of different THz generation mechanisms, the mechanisms for the THz generation pumped at 400 nm in GaSe thin films are induced by optical rectification and photoexcited carriers accelerated by built-in electric field in the films.