脉冲激光沉积方法生长硅基ZnO薄膜的特性

用脉冲激光沉积法(PLD)在n型硅(111)平面上生长ZnO薄膜.X射线衍射(XRD)在2θ=34°处出现了唯一的衍射峰,半高宽为0.75°;傅里叶红外吸收(FTIR)在414.92cm-1附近出现了对应Zn-O键的红外光谱的特征吸收峰;光致发光(PL)测量发现了位于370和460nm处的室温光致发光峰;扫描电子显微镜(SEM)和选区电子衍射(SAED)显示了薄膜的表面形貌以及晶格结构.利用PLD法制备了具有c轴取向高度一致的六方纤锌矿结构ZnO薄膜.     

Photoluminescence characterization of AlGaN-GaN pseudomorphic quantum wells and calculation of strain induced bandgap shifts

The low temperature (77 K) photoluminescence characteristics of Al _x Ga_1-x N-GaN strained layer quantum wells with differentx values grown by metalorganic chemical vapor deposition (MOCVD) were investigated. The photoluminescence spectra were useful in analyzing both quantum confinement effects and strain induced energy shifts. The strain induced shifts were found to be a strong function of aluminum compositionx. A model was developed to calculate the strain induced bandgap shifts atk = 0. The values predicted by this model which took into account the wurtzite crystal structure of the material system, were in good agreement with (i.e. within 2 meV of) the experimentally measured shifts.     

用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性结果的比较

报道了分别用三带和全带模型蒙特卡罗方法模拟纤锌矿相GaN体材料输运特性的结果,并对基于两种模型的模拟结果进行了比较.在低场区,基于两种模型获得的输运特性基本相同,但在高场区却表现出明显的差别.这是因为在高场区,电子平均能量较高,多数电子处于能带图中的高能态位置,电子能量与波矢量的关系表现出明显的非椭圆特性.由于三带模型假定了能量与波矢量简单关系,故算得的平均能量,高于由全带蒙特卡罗模拟算得的能量.从而导致其它特性的差别.全带模型包含了基于能带理论算得的能带结构的所有特性,故模拟结果更加精确.     

Growth and Optical Properties of Quantized CdS Crystallites in TEOS Silica Xerogels

Quantized CdS crystallite-doped tetraethylorthosilicate (TEOS) silica xerogels are prepared by the sol-gel method. In this method, cadmium acetate [Cd(CH₃COO)₂2H₂O]-doped TEOS alcogel is formed by the hydrolysis and polycondensation of ethanolic TEOS in the presence of hydrochloric acid (HCl) and ammonium hydroxide (NH₄OH) catalysts and Cd(CH₃COO)₂.2H₂O. The CdS crystallites are formed in the alcogel by the reaction of Cd(CH₃COO)₂.2H₂O present in the gel and methanolic sodium sulfide (Na₂S), which is added over the alcogel. The effect of CdS/TEOS, EtOH/TEOS, S/Cd molar ratios, and temperature on the optical properties and CdS crystallite sizes in the xerogels are studied. A blue shift is observed in optical absorption spectra by decreasing the CdS/TEOS molar ratio from 2 × 10^–2 to 1 × 10^–4. It is observed that the crystallite size is increased from 1.6 to 3.4 nm by increasing the EtOH/TEOS molar ratio from 2 to 20, respectively, for a constant CdS/TEOS molar ratio of 5 × 10^–4. Emission spectra of xerogels are measured and found that the emission peak maxima shifted toward lower energies (higher wavelengths) by increasing the CdS/TEOS molar ratio in the xerogels. It is known from the X-ray diffraction (XRD) measurements of CdS-doped xerogels that the CdS crystallite structure in the xerogels is hexagonal wurtzite. The crystallite sizes were calculated from the XRD patterns and tight bonding calculations. There is a significant change in the color and size of CdS crystallite in the xerogels with a variation in temperature from 200 to 400°C.     

Structural Stabilization and Piezoelectric Enhancement in Epitaxial (Ti1−xMgx)0.25Al0.75N(0001) Layers

Epitaxial (Ti_1?xMg_x)_0.25Al_0.75N(0001)/Al₂O₃(0001) layers are used as a model system to explore how Fermi‐level engineering facilitates structural stabilization of a host matrix despite the intentional introduction of local bonding instabilities that enhance the piezoelectric response. The destabilizing octahedral bonding preference of Ti dopants and the preferred 0.67 nitrogen‐to‐Mg ratio for Mg dopants deteriorate the wurtzite AlN matrix for both Ti‐rich (x < 0.2) and Mg‐rich (x ≥ 0.9) alloys. Conversely, x = 0.5 leads to a stability peak with a minimum in the lattice constant ratio c/a, which is caused by a Fermi‐level shift into the bandgap and a trend toward nondirectional ionic bonding, leading to a maximum in the expected piezoelectric stress constant e₃₃. The refractive index and the subgap absorption decrease with x, the optical bandgap increases, and the elastic constant along the hexagonal axis C₃₃ = 270 ± 14 GPa remains composition independent, leading to an expected piezoelectric constant d₃₃ = 6.4 pC N^?1 at x = 0.5, which is 50% larger than for the pure AlN matrix. Thus, contrary to the typical anticorrelation between stability and electromechanical coupling, the (Ti_1?xMg_x)_0.25Al_0.75N system exhibits simultaneous maxima in the structural stability and the piezoelectric response at x = 0.5.     

纤锌矿型氧化锌电子结构的第一性原理计算

采用基于密度泛函理论(DFT)框架下局域密度近似平面波超软赝势法,计算了纤锌矿型ZnO的能带结构、态密度和复介电常数,计算结果与其他文献结果吻合较好,并从理论上分析了它们之间的关系。结果表明,纤锌矿型ZnO在(100)和(001)方向上具有光学各向异性,为纤锌矿型ZnO的应用提供了理论依据。     

纤锌矿结构GaAs(1010)表面特性的第一性原理研究

GaAs纳米线通常呈现纤锌矿结构(WZ),而WZ(1010)侧面已被实验所观测到。利用第一性原理计算了GaAs(1010)的表面弛豫和表面能,计算结果表明:(1010)A表面只出现原子的弛豫现象,表面能为40.6×1020meV/m2;而(1010)B表面却重构形成了GaGa和AsAs二聚体,表面能为63.5×1020meV/m2。相对于ZB(110)表面,WZ(1010)A面具有更低的表面能,(1010)A表面具有更好的稳定性,说明了在表面能占重要影响的纳米线中WZ结构存在的合理性。     

First-principles study of the electronic structures and optical properties of C-F-Be doped wurtzite ZnO

正The electronic structure and optical properties of pure,C-doped,C-F codoped and C-F-Be clusterdoped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft pseudopotentials method.The results indicate that p-type ZnO can be obtained by C incorporation,and the energy level of C_O above the valence band maximum is 0.36 eV.The ionization energy of the complex Zn_(16)O_(14)CF and Zn_(15)BeO_(14)CF can be reduced to 0.23 and 0.21 eV,individually.These results suggest that the defect complex of Zn_(15)BeO_(14)CF is a better candidate for p-type ZnO.To make the optical properties clear,we investigated the imaginary part of the complex dielectric function of undoped and C-F-Be doped ZnO.We found that there is strong absorption in the energy region lower than 2.7 eV for the C-F-Be doped system compared to pure ZnO.     

纳米ZnO的沉淀法制备、表征及影响因素分析

用Zn(NO₃)₂·6H₂O对作原料、Na₂CO₃作沉淀剂,制得了纳米ZnO粉体.用TG-DSC、XRD和TEM分别对前驱体和纳米ZnO粉体进行了表征.结果表明:所得前驱体在253℃左右分解为六方纤锌矿型纳米ZnO,颗粒大小约为15～20nm,粒径分布窄,基本无团聚,粉体的比表面积为64.12m²·g^-1实验发现,当反应物浓度从2.0mol·L^-1减小至1.0、0.5mol·L^-1时,纳米ZnO粉体的粒径基本无变化,但颗粒间的团聚状态减轻;在用无水乙醇洗涤沉淀前,先用蒸馏水或稀氨水清洗对得到的纳米ZnO粉体的团聚状态没有明显的区别.