Zn1-xCdxSe/ZnSe半導體量子井之光學性質研究

Abstract

我的論文是利用光激螢光譜、反射光譜、拉曼光譜及穿透式電子顯微鏡，來研究由分子束磊晶法製作的半導體量子井 Zn1-xCdxSe/ZnSe 之光學性質。 實驗可分為下列幾部分： 一、 利用量子力學中有限深位能井的模型，模擬Zn1-xCdxSe/ZnSe 量子井構造， 計算量子井中價帶和導帶可能侷限的能階大小，再考慮激子的束縛能，得到量子井可能的發光能量。再把理論的結果跟由光激螢光譜得到的實驗結果比對，求得量子井組成成分參數 X。 二、 因為純粹的Zn1-xCdxSe/ZnSe 量子井構造在室溫時，發光的效率和品質並不好，所以我們引進 ZnMgSSe 當作包覆層，利用它有較高能階和較小折射率的特性來束縛光場，同時也利用增加量子井的數目，來改進樣品的發光效率，由實驗的結果可以證明這個方法是有效的。 三、 由於在加入 ZNMgSSe 時，硫原子會侵害基板 GaAs 的表面，所以我們使用超晶格 ZnSSe/ZnSe 、ZnSe 和 GaAs 來當作緩衝層，減少缺陷的產生。實驗的結果顯示，緩衝層能夠有效的提高發光效率、縮小發光光譜的半高寬，改善發光品質。 四、 為了確定各層薄膜的組成成分，和它們的結晶品質。我們使用拉曼光譜測量它們的聲子振動能量，因為各種薄膜有其各自的聲子振動能量，不會隨溫度而變，所以我們可以用來確定薄膜的組成成分。而由光譜的半高寬，可以判斷結晶品質的好壞。

In this work, we use the Photoluminescence (PL), Reflection, Raman spectroscopy measurement and transmission electron microscopy (TEM) to study the optical properties of Zn1-xCdxSe/ZnSe semiconductor quantum wells that were grown by Molecular Beam Epitaxial (MBE) system. Experiments have three parts： I. We use the finite quantum well model to imitate the Zn1-xCdxSe/ZnSe quantum well structure. Then, we calculate the quantum well confinement energies in the valence band and conduction band. We also introduce the excitonic binding energies in the calculation. Thus, we get the emission energies of the quantum well. These results are compared with the PL spectra and then we can determine composition parameters x of the quantum wells. II. The emission energies of the Zn1-xCdxSe/ZnSe QWs at room temperature are not high enough to obtain higher luminescence. Therefore, we introduce the ZnMgSSe as the cladding layer and use its smaller refractive index than ZnSe to confine optical field within the active region (QWs). We also increase the layers of quantum well to enhance the emissive intensity. The experimental results prove that this way is effective. III. When we used the ZnMgSSe guide layer to enhance emissive intensity, deoxidized GaAs surfaces were attacked by sulfur atoms. Therefore, we introduce the strain layer superlattice buffers, ZnSe/ZnSSe, and buffer layers, ZnSe、GaAs, to suppress the generation of defects. The results show that the buffer layers enhance the efficiency and of quality emission successfully, and also reduce the PL peak full width at half maximum (FHWM) effectively. IV. In order to ascertain the thin films of each layer crystalline quality and their compositions, we use the Raman spectroscopy measurement. We measure the phonon vibration energies of each layer. These phonon vibration energies are peculiar to thin films, and they do not vary with the temperature. Thus, we can use Raman spectra to ascertain the composition of each thin film and use Raman spectra peak full width at half maximum (FHWM) to appraise their crystalline quality.