高品質氧化鋅、氧化鎂鋅、氧化錳鋅與氧化鎘鋅之成長與光學研究

Abstract

本篇論文利用電漿輔助式分子束磊晶系統在藍寶石基板上成長高品質氧化鋅、氧化鎂鋅、氧化錳鋅與氧化鎘鋅薄膜，並利用光頻譜量測技術探討樣品的光學特性。 在氧化鋅部分，利用固定氧氣流量，調控鋅元素流量，成長出不同參數之氧化鋅薄膜。經由光激螢光光譜量測，得到一組氧化鋅薄膜發光最佳品質之樣品。接續的氧化鋅摻雜鎂、錳與鎘等元素之氧化鋅合金材料皆以此最佳品質之氧化鋅薄膜參數去成長。在氧化鎂鋅部分，成長出鎂濃度最高為11.2%之高品質氧化鎂鋅薄膜。此外，利用氧化鎂與氧化鋅兩層緩衝層以及熱退火方法可以改善氧化鎂鋅之薄膜的平整度。另一方面，我們也成功利用鎂濃度8.3%之氧化鎂鋅成長出氧化鋅/氧化鎂鋅量子井。 氧化錳鋅部分，成長出錳濃度最高為6.1%之高品質氧化錳鋅薄膜。在共振拉曼光譜中我們發現氧化鋅樣品和氧化錳鋅樣品各自有5個和11個縱向光學聲子的訊號。藉由變溫共振拉曼光譜的實驗，可以得知縱向光學聲子訊號的強度與氧化錳鋅的能隙位置相關。除此之外，我們也對摻雜錳濃度0.3%的氧化錳鋅薄膜量測在磁場下的光激螢光光譜，在外加磁場5T時有9%的圓形極化率。 氧化鎘鋅部分，利用變溫光激螢光光譜與時間解析光激螢光光譜探討鎘濃度2%之氧化鎘鋅內部載子受熱效應影響下的躍遷行為。當基板溫度降低至350℃後，利用調控鎘與鋅的原子源流量比例即可成長出鎘含量為49.7%之高濃度且高品質之氧化鎘鋅薄膜。此系列的氧化鎘鋅薄膜的發光範圍涵蓋了可見光。此外也利用變溫光激螢光光譜探討載子在材料中受溫度影響後的躍遷行為。最後我們成長漸變濃度之氧化鎘鋅薄膜，利用光激螢光光譜與時間解析光譜量測技術定義出漸變濃度的氧化鎘鋅螢光的來源。除此之外，利用紅綠藍三色混光的的方法，此樣品發出的螢光在肉眼觀察下是白光而且室溫下材料的內部量子效率為33.67%。

In this dissertation, the growth of high quality ZnO, ZnMgO, ZnMnO and ZnCdO thin films on Al2O3 substrate by plasma-assisted molecular beam epitaxy were studied. The photoluminescence (PL), transmittance and time-resolved photoluminescence (TRPL) were used to investigate the optical properties. For the growth of Zn1-xMgxO (x=0~0.112) thin films, MgO buffer is used to improve the surface morphology during the initial growth stage, which eventually leads to an atomically flat surface. ZnO/ZnMgO multiple quantum wells were also fabricated successfully on the atomically flat MgO surface. In the case of Zn1-xMnxO (x=0~0.061) thin films, transmittance spectra show an increase of band gap with the increasing Mn concentration. Resonant Raman scattering spectra showed 11 longitudinal optical phonon lines for the Zn1-xMnxO samples. In addition, circular polarization degree of 9 % was observed in the Zn0.997Mn0.003O sample at magnetic field B=5 T. Furthermore, the growth of high quality Zn1-xCdxO thin films with visible light emission was achieved at growth temperature of 350 ℃. The concentration of Cd can be systematically adjusted via the Cd/Zn beam pressure ratio and the maximum concentration was 49.7 %. The origin of radiative recombination and dynamics of the charge carriers in the graded Zn1-xCdxO multilayers was investigated by means of PL and TRPL spectroscopy. The internal quantum efficiency of our sample achieved 33.67 %.