以拉曼頻譜探悉砷化銦之光學特性

Abstract

本論文研究主題為以拉曼散射觀察不同濃度砷化銦光學特性，由拉曼頻譜中觀察到自由載子和縱向光學聲子耦合產生縱向光學模態，並由實驗裡觀察到縱向光學聲子的信號，以波向量說明LO訊號是來自砷化銦表面電子累積層的貢獻；L_則是來自累積層以外的區域。 於變功率量測下，低摻雜濃度砷化銦較容易受到雷射激發載子的影響，其LO-plasmon couple mode (L_)因激發載子的影響，有一逆向電場形成，讓原本在表面電子累積層的電場減小，影響累積層的厚度；高摻雜濃度砷化銦，其雷射功率影響並不顯卓，由LO以及L_強度分析，推測激發載子濃度與本質濃度接近，推測累積層幾乎維持不變。

In this thesis, we use Raman spectroscopy to investigate the lattice vibrational modes of InAs grown by molecular beam epitaxy (MBE). The Raman spectra of InAs epilayers for various carrier concentrations shows that the carriers strongly interact with the LO mode for n-type semiconductors, which results in coupled plasmon modes (L_) and the unscreened LO phonon mode within the accumulation layer on the surface. With the variety of laser power excitation, we observe the undoped InAs sample strongly dependent on the incident power. The LO-plasmon couple mode (L_) reduces the surface field due to the photo-generated carriers. The thickness of the accumulation layer therefore become thinner. Compared to the undoped sample, the heavily doping InAs has little effect on the incident power and the thickness nearly remains constant because the amount of the photo-generated carriers is nearly equal to the doping concentration. .