利用脈衝雷射蒸鍍法製備不同厚度碲化鉍薄膜與其兆赫波時域頻譜研究

Abstract

在本論文中，我們嘗試利用脈衝雷射蒸鍍法調控脈衝發數將不同厚度碲化鉍薄膜成功的長在藍寶石(0001)基板上。隨後利用XRD、Raman、EDS來量測碲化鉍的晶格結構、薄膜品質與碲、鉍間之組成比例。接著量測低溫外加磁場的情況下薄膜電阻率得到隨厚度變化為一定值的相位相干長度，得到貢獻之載子大部分來自於表面態，且用兆赫波時域頻譜來研究此薄膜在兆赫波頻段下的電磁特性。利用量測數據與理論分析可獲得此薄膜材料在各種不同厚度之下的光學常數，再透過Drude-Lorentz模型來進行數學擬合，並得到碲化鉍薄膜之聲子模態振動頻率、電漿頻率以及散射率。最後我們會將兆赫波輻射經過不同厚度下的碲化鉍薄膜所得到的光電常數與厚度之間的關係。

In this work, we have prepared Bi2Te3 thin film grown on sapphire (Al2O3) (0001) substrates by pulsed laser deposition (PLD) with pulse control for varying thicknesses. The Bi2Te3 thin film quality, structure and Bi/Te ratio analyzed by X-ray diffraction (XRD), Raman spectroscopy and Energy dispersive spectrometer (EDS). Also, we measure resitivities of thin films at low temperature by applying magnetic field. The thickness independent phase coherent length at 2K shows that the carriers are mostly from surface channels. Moreover, we have used time-domain terahertz spectroscopy to investigate the low-frequency complex conductivity in Bi2Te3 thin film at different thicknesses. The thickness dependent terahertz conductivity of optimized Bi2Te3 thinfilm can be fitted with Durde-Lorentz model. Finally, we can observe that the relationship of optical constants with varying thicknesses, including the phonon oscillator frequency, plasma frequency and scattering rate.