金屬有機化學氣相沉積磊晶氧化鋅薄膜於氧化物單晶基板之研究

Abstract

本論文主要的方向在於利用化學氣相沉積法成長氧化鋅磊晶薄膜於YSZ(111) (yttria-stabilized zirconia)基板、ScAlMgO4(0001)基板(簡稱SCAM)以及GaN/c-Al2O3基板上，方法包含金屬有機化學氣相沉積法(metalorganic chemical vapor deposition, MOCVD)以及原子層化學沉積法(atomic layer deposition , ALD)。

MOCVD實驗方面，以YSZ(111)為基板改變成長溫度以及成長時間，探討在不同溫度下，氧化鋅薄膜的形貌、晶體結構及發光特性的差異；在不同時間探討成核階段與成長階段薄膜晶體品質的差異，與形貌上的變化，藉此了解氧化鋅薄膜於YSZ基板上的成核成長機制；並嘗試以兩階段方式改善表面粗糙度。以ScAlMgO4為基板成長出幾近同質磊晶氧化鋅薄膜，改變成長溫度，觀察不同溫度下薄膜形貌上的變化，以及薄膜品質的差異。ALD實驗方面，以GaN/c-Al2O3為基板，在300 □C下成長出氧化鋅薄膜。 分析方面，以掃描式電子顯微鏡(scanning electron microscopy, SEM)、原子力顯微鏡(Atomic force microscopy, AFM)觀察表面形貌，以X光繞射儀(X-ray diffractometer, XRD)、高解析X光繞射儀(High-resolution X-ray diffractometer, HRXRD)、穿透式電子顯微鏡(Transmission electron microscopy, TEM)、高解析電子顯微鏡(High-resolution transmission electron microscopy, HRTEM)鑑定晶體結構，以低溫光子激發光譜(photoluminescence, PL)分析發光特性。 MOCVD實驗結果，在YSZ 上沉積ZnO，基材溫度500 □C可以成長出平滑薄膜最小粗糙度0.37 nm；溫度升高成長模式由二維方式轉向三維方式成長，薄膜表面可見氧化鋅六角形晶粒。於500 □C不同成長時間均能獲得相當好的磊晶薄膜；於600℃只能在短時間成長得到較佳磊晶品質，時間增長磊晶品質有變差的趨勢。薄膜有基材間具有磊晶關係，(0002)ZnO∥(111)YSZ、[ ]ZnO∥[220]YSZ。PL發光特性，有很強的峰值訊號近能隙邊緣在3.36 eV出現，而綠光訊號只在短時間600 □C成長出現。 在SCAM基材上沉積ZnO，在400 □C及500 □C薄膜成長均為2D(layer-by-layer)型式，薄膜表面均相當平整；當溫度提高至600 □C，成長模式為多層成長(multilayer growth)。於600 □C得到極佳品質之磊晶薄膜，XRD (0002) 搖滾曲線(rocking-curve) 之半高寬(full-width at half-maximum. FWHM)約為60 arcsec；氧化鋅晶粒形狀亦具有六重對稱性。 ALD方面，在YSZ上不容易成長出單晶氧化鋅薄膜，易成長出多晶薄膜。在GaN上，於300 □C可獲得磊晶氧化鋅薄膜。

In this study, epitaxial ZnO films were grown by metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). ZnO films on yttria-stabilized zirconia (YSZ) and ScAlMgO4 were deposited by MOCVD at various temperatures. Two-step growth were used to improve the surface smoothess. Besides, ZnO films on YSZ, c-sapphire and GaN/c-Al2O3 were deposited by ALD at various temperatures. The structure properties of ZnO thin films were characterized by X-ray diffraction (XRD)、high-resolution X-ray diffraction (HRXRD)、transmission electron microscopy (TEM)、high-resolution transmission electron microscopy (HRTEM). The surface morphology was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optical properties was measured by low temperature photoluminescence (PL). For MOCVD, it is found that ZnO growth mode is switched from 2D growth to 3D growth as the substrate temperature is increased. For the ZnO deposited on YSZ at 500 and 600 □C, all samples show the same epitaxial relationship between the films and substrates : (0001)ZnO||(111)YSZ. For ZnO grown on YSZ, the 600oC deposition resulted in the best crystal quality films. The films with the smallest surface roughness were obtained by deposition at about 500 □C. For ZnO thin films on ScAlMgO4 substrates grown by MOCVD, the smallest surface roughness could be obtained at 400 and 500 □C. When the temperature increased to 600 □C, the surface morphology shows the six-fold symmetry of hexagonal ZnO crystallites and the growth mode is 3D. For two- steps growth, flat ZnO thin films were obtained. For ZnO deposition by ALD, no epitaxial ZnO films were grown on YSZ substrate. However, epitaxial ZnO films can be formed on GaN/Al2O3 substrate at 300 □C.