氧化銦錫奈米結構兆赫頻段光學特性與電性之研究

Abstract

我們使用兆赫波時域光譜的光學量測方法去探討氧化銦錫奈米柱的光學特性和電性。首先，我們分別量測了樣品以及基版的兆赫波時域訊號，藉由傅立葉轉化成頻域訊號後分析可以得到不同厚度氧化銦錫奈米柱0.2~2(THz)複數的折射係數，而複數的折射係數可以轉換成複數的導電率，以Drude-Smith模型來擬合實驗的導電率。我們得到樣品的電漿頻率，其值為74~396(rad□THz)，載子的散射時間為34~68(fs/rad)，另外，Drude-Smith模型的電子碰撞參數c大於 -0.4。這種光學量測方法可以得到各種奈米結構材料的電性，我得到對應的載子漂流率跟載子濃度，分別為100~400 cm2/Vs 和0.05×1019~1.5×1019。和傳統的霍爾量測或四點探針比起來，兆赫波時域光譜的光學量測方法是非接觸式且不會破壞樣品的表面，藉由Drude-Smith模型的輔助我們可以得到奈米結構材料的電性。

We have investigated the optical and electrical properties of Indium Tin Oxide (ITO) nanocolumns by using terahertz time domain spectroscopy (THz-TDS). First, we measured the THz time domain waveform for both sample and reference. After transforming into frequency domain, we extracted the frequency dependence complex refractive index. Second, we can determine the experimental complex conductivity by complex refractive index. With fitting the real and image part of conductivity by Drude-Smith model, we finally extract the fitting parameters such as plasma frequency, scattering time and Drude-Smith constant c. In this work, we obtained the plasma frequency of ITO nanocolumns is around 74~396 rad□THz, and the scattering time is around 34~68 fs. Moreover, the electron original velocity fraction coefficient is larger than -0.4. The electrical properties of ITO nanocolumns derived from non-contact optical techniques have been determined. The mobility is 100~400 cm2/Vs and the carrier concentration is 0.05×1019~1.5×1019 cm-3. Comparing with conventional Hall or four probe measurement, THz-TDS is a non-contact method and the electrical properties of nanostructure material can be derived from the experimental conductivity by fitting with the Drude-Smith model.