- 學位論文
利用脈衝雷射沈積法在砷化鎵(100)上製作硒化鋅與碲化鎘薄膜-背景壓力的影響
Influence of Background Pressure In ZnSe And CdTe Thin Films Grown On GaAs (100) Using Pulsed Laser Deposition
摘要
本論文利用脈衝雷射沉積技術(PLD)成長二六族化合物半導體硒化鋅(ZnSe)化合物與碲化鎘(CdTe)薄膜。藉由原子力顯微術與掃瞄式電子顯微術探討薄膜表面形貌，再利用X光繞射(XRD)、光反射譜(PR)、光激螢光譜(PL)、拉曼散射譜等技術進行薄膜的物性分析。 首先，探討雷射功率與成長溫度對於硒化鋅薄膜的影響，尋找出利用脈衝雷射成長硒化鋅薄膜最適當的成長窗。發現脈衝雷射功率180 mJ與成長溫度410 ℃的成長條件可以獲得較平坦與結晶性較佳之硒化鋅薄膜。進一步藉由通入高純度氮氣改變成長腔的背景壓力，探討背景壓力對硒化鋅薄膜成長的影響。我們發現背景壓力的改變，會改變羽狀電漿流量與遷移長度，進而影響薄膜成長速率與結晶品質。藉由反射譜與光激螢光譜發現其近能隙發光能量隨著背景壓力增加而產生紅位移，而且硒化鋅黃光缺陷發光強度被大幅抑制。觀察拉曼散射譜發現背景壓力越高，硒化鋅的縱向光學聲子（LO）與橫向光學聲子（TO）的強度都隨之增加，而且硒化鋅的LO聲子隨著背景壓力增加往低頻位移，而半寬則相對變小。 第二部份, 通入氮氣改變背景壓力在砷化鎵基板上成長碲化鎘薄膜。碲化鎘成長分為二個系列，一為在砷化鎵基板上先沉積一層砷化鎵緩衝層，之後在緩衝層上沉積碲化鎘薄膜；二為直接在砷化鎵基板上沉積碲化鎘薄膜。藉由光激螢光譜與反射譜發現有緩衝層的碲化鎘薄膜其低溫的近能隙放光位置約在1.515 eV，遠低於文獻所提的1.58 eV，推測可能是多晶相轉變所造成。而在沒有緩衝層系列的樣品中，發現在較低的背景壓力可以使結晶趨向於閃鋅礦結構。
並列摘要
In this thesis, ZnSe and CdTe Ⅱ-Ⅵ compound semiconductors thin films were grown on GaAs(100) useing pulsed laser deposition (PLD). The surface morphology of ZnSe and CdTe thin films are characterized by atomic force microscope (AFM) and scanning electron microscope (SEM). X-ray diffraction (XRD), photo-reflectance (PR), photoluminescence (PL), and Raman scattering spectrum are employed to measure the physical properties. Firstly, the influence of laser power density and growth temperature in PLD to figure out the ZnSe growth window. The optimized condition for ZnSe were the laser power density at 180 mJ and growth temperature at 410°C, respectively. The background pressure was controlled by the introduced nitrogen flow to explore the influence of background pressure in ZnSe thin films. The magnitude of plume plasma and atomic migration length are correlated to the background pressure. Additionally, the growth rate and crystallization are influenced. In PR and PL spectra, the near band edge emission of ZnSe were red-shifted with raised background pressure. Further, the ZnSe yellow band (defect emission) is suppressed. In Raman scattering spectra, the intensity of longitudinal optical phonon (LO) and transverse optical phonon (TO) increased with raised background pressure. The LO phonon was inclined to the low frequency. Secondly, the CdTe films were deposited on GaAs substrate with varying the background pressure. There are two groups of CdTe thin films. The difference between them is the consisted GaAs buffer layer. The near band edge emission of CdTe with GaAs buffer is determined at around 1.515 eV using PR and PL measurement. This value is lower then the band gap of CdTe (1.58 eV) may cause by the phase separation or the mixed by GaAs and CdTe. Furthermore, the crystallization of CdTe samples without GaAs buffer trend toward the zinc blende structure at lower background pressure.