MgxZn1-xO合金制备及MgZnO/ZnO异质结构的光学性质

利用射频等离子体辅助的分子束外延(P-MBE)技术在c面的蓝宝石衬底上生长了具有不同Mg含量(0≤x≤0.28)的六方相MgZnO合金薄膜,研究了该系列样品Raman频移的幅度与合金组分的对应关系,为MgZnO合金中Mg含量的确定提供了新的方法。在此基础上选择具有合适带宽的MgZnO合金作为垒层,制备了MgZnO/ZnO量子阱结构。在较高的光激发密度下,观测到了发光强度随激发密度的超线性增加,并将之归因于激子-激子碰撞引起的超辐射过程。     

应变纤锌矿ZnO/MgxZn1-xO盘形量子点中的离子施主束缚激子态

在有效质量近似下,计算了盘形量子点中离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命.设盘形量子点由有限长的柱形ZnO材料组成,四周被Mgx Zn1xO包围,离子施主局域在盘轴.考虑了由于自发极化和压电极化引起的内建电场效应,并在有限深约束势下采用合适的变分波函数进行.计算结果表明,量子盘结构参数(盘高度及垒中Mg组分)和离子施主的位置对离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命有强烈的影响.随着盘高度的增加,结合能、光跃迁能和振子强度减小,而辐射寿命增加.对含Mg量较高的盘形量子点,盘高度对结合能、光跃迁能、振子强度及辐射寿命的影响更显著.当施主杂质位于量子点的左界面附近时结合能(光跃迁能)有极大(极小)值,而当施主杂质位于量子点的右界面附近时结合能(光跃迁能)有极小(极大)值.     

外电场对InGaAsP/InP量子阱内激子结合能的影响

在有效质量近似下采用变分法计算了InGaAsP/InP量子阱内不同In组分下的激子结合能,分析了结合能随阱宽和In组分的变化情况,并且讨论了外加电场对激子结合能的影响. 结果表明：激子结合能是阱宽的一个非单调函数,随阱宽的变化呈现先增加后减小的趋势;随着In组分增大,激子结合能达到最大值的阱宽相应变小,这与材料的带隙改变有关;在一定范围内电场的存在对激子结合能的影响很小,但电场强度较大时会破坏激子效应. 关键词： 激子 InGaAsP/InP量子阱 结合能 电场     

应变纤锌矿ZnO/Mg_xZn_(1-x)O盘形量子点中的离子施主束缚激子态（英文）

在有效质量近似下,计算了盘形量子点中离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命.设盘形量子点由有限长的柱形ZnO材料组成,四周被MgxZn1-xO包围,离子施主局域在盘轴.考虑了由于自发极化和压电极化引起的内建电场效应,并在有限深约束势下采用合适的变分波函数进行.计算结果表明,量子盘结构参数(盘高度及垒中Mg组分)和离子施主的位置对离子施主束缚激子的结合能、光跃迁能、振子强度及辐射寿命有强烈的影响.随着盘高度的增加,结合能、光跃迁能和振子强度减小,而辐射寿命增加.对含Mg量较高的盘形量子点,盘高度对结合能、光跃迁能、振子强度及辐射寿命的影响更显著.当施主杂质位于量子点的左界面附近时结合能(光跃迁能)有极大(极小)值,而当施主杂质位于量子点的右界面附近时结合能(光跃迁能)有极小(极大)值.     

利用P-MBE制备高质量MgxZn1-xO的结构和光学特性

利用等离子体辅助分子束外延(P-MBE)的方法,在c平面的蓝宝石衬底上制备了高质量的MgxZn1-xO合金薄膜。通过改变Mg源的温度,得到了不同Mg组份的MgxZn1-xO合金薄膜;通过引入ZnO的低温缓冲层,有效地提高了MgxZn1-xO合金薄膜的结晶质量。随着Mg组份的增加,MgxZn1-xO的X射线衍射的(002)衍射峰逐渐向大角度方向移动。对样品进行光致发光(PL)谱的测量,在室温下观察到了较强的紫外发光。随Mg浓度的增加,紫外发光峰向高能侧移动,并且发光峰逐渐展宽。通过对x=0.15的样品进行变温光谱的测量研究了紫外发光峰起因,得到了MgxZn1-xO的发光是来自于自由激子的发光。自由激子束缚能为54meV。     

ZnCdSe/ZnSe非对称双量子阱中的光学特性研究

用LP-MOCVD技术在GaAs衬底上外延生长了ZnCdSe/ZnSe非对称双量子阱(ADQW)结构。通过ps时间分辨光谱、吸收光谱、发射光谱等的研究得到了如下的结果:在弱激发下,观测到ADQW结构中的激子隧穿现象;在强激发下,在ADQW结构中发现了一个内建电场,它将影响激子隧穿;首次观测到由激子隧穿引起的在一定温度范围内宽阱的发光强度随温度上升而增加的现象;首次观测到该ADQW结构中来自宽阱的光泵受激发射。     

基于给体/受体有机太阳电池性能的研究

以酞菁铜(CuPc)、对北艹四甲酸二酐(PTCDA)和富勒烯(C60)作为光敏材料分别制备了3个有机太阳电池器件:器件1为ITO/PEDOT(3,4-乙撑二氧噻吩)/CuPc/Al;器件2为ITO/PEDOT/CuPc/PTCDA/Al;器件3为ITO/PEDOT/CuPc/C60/Al.研究发现器件2、3的短路电流和开路电压比1的提高了很多,主要是因为2、3是给体/受体异质结构,它不仅增大了器件的吸收光谱并提供了一个激子解离的有效位置.器件2和3相比,3的短路电流和开路电压比2的提高了1倍多,这主要是因为C60的激子扩散长度比PTCDA的要长,激子解离的几率比激子复合的几率大得多,因此3的性能比2的有了很大的提高.     

应变纤锌矿ZnO/Mg_xZn_(1-x)O柱形量子点中离子受主束缚激子的光学性质

在有效质量近似下,考虑内建电场效应,采用变分法详细研究了受限于纤锌矿Mg_xZn_(1-x)O/ZnO/Mg_xZn_(1-x)O圆柱形应变量子点中离子受主束缚激子(A~-,X)的带间光跃迁吸收系数随量子点尺寸、Mg含量和离子受主杂质中心位置的变化情况,并和离子施主束缚激子(D~+,X)及自由激子进行了比较.结果表明:随着量子点尺寸的减小,(A~-,X)的光跃迁吸收强度增强,吸收曲线向高能方向移动,出现蓝移现象.随着Mg含量增加,(A~-,X)的光跃迁吸收曲线蓝移,且吸收强度减弱.随着离子受主杂质从量子点的左界面沿材料生长方向移至量子点的右界面,光跃迁吸收曲线向低能方向移动,出现红移现象.此外,与离子施主束缚激子(D~+,X)相比,随着沿材料生长方向掺入杂质位置的变化,光跃迁吸收曲线移动的方向相反.但不管是掺入离子受主杂质还是离子施主杂质,当离子杂质从量子点的左异质界面沿材料生长方向移至右异质界面时,光跃迁吸收峰的移动量大致相同.     

ZnSe/SiO2半导体量子点玻璃的光谱特性

对采用溶胶凝胶法制备的ZnSe/SiO2半导体量子点玻璃的光谱性质进行了测试分析.UV-Vis透射光谱中观察到光吸收边相对于体相半导体有明显蓝移.稳态发射光谱(PL)中观察到ZnSe纳米晶体的位于蓝区的基本呈高斯分布的弱的最低激子发射峰、强而宽的表面态发光带以及对应杂质能级的三个锐峰发光.时间分辨荧光光谱(TRPL)中观察到发光效率高的最低激子发射峰,并测量其荧光衰减寿命,经尾部拟合为28.5 ps.同时,结合有效质量近似(EMA)模型,估计ZnSe纳米晶体的平均粒径介于2.45~3.60 nm之间,尺寸分布基本呈高斯型.     

In组分对InGaN/GaN蓝光LED的发光性质的影响

利用扫描透射电子显微术(STEM)和变温光致发光光谱(PL)研究了In组分对InGaN/GaN蓝光LED的发光的影响.STEM发现两个样品量子阱结构相同,低温PL显示低In组分的样品的发光峰位随着温度的升高呈现出经典S(Red-Blue-Red)曲线.目前普遍认为蓝移是In组分分布不均匀造成的局域激子发光的主要原因,然...     

Third-order optical nonlinearities of Zn1-xMgxO thin films

The Zn1-xMgxO thin films were deposited on sapphire substrates by reactive electron beam evaporation deposition (REBED). The X-ray diffraction (XRD) measurement demonstrates that these films undergo phase transition from hexagonal to cubic with increasing the Mg concentration. Absorption coefficients at 532 nm of the samples were obtained from the absorption spectra. Using optical Kerr effect, the thirdorder susceptibilities of the ternary films over a wide range of Mg concentrations were determined. The magnitude of x(3) of the ternary Zn1-xMgxO films is order of 10-11 esu at λ = 532 nm. The sample with phase mixture of both hexagonal and cubic structures shows the largest third-order susceptibility. The difference observed in the magnitude of x(3) of Zn1-xMgxO films is attributed to the different microstructures of the ternary films, such as crystalline phase separation and crystal grains that enhance stimulated scattering.     

Size dependent effective band gap,optical absorption coefficients and refractive index changes in a wide ZnS/Zn1−xMgxS strained quantum well

Exciton binding energy of a confined heavy hole exciton is investigated in a Zn_1−xMg_xS/ZnS/Zn_1−xMg_xS single strained quantum well with the inclusion of size dependent dielectric function for various Mg content. The effects of interaction between the exciton and the longitudinal optical phonon are brought out. The effect of exciton is described by the effective potential between the electron and hole. The interband emission energy as a function of well width is calculated for various Mg concentration with and without the inclusion of dielectric confinement. Non-linear optical properties are carried out using the compact density matrix approach. The dependence of nonlinear optical processes on the well width is investigated for different Mg concentration. The linear, third order non-linear optical absorption coefficients values and the refractive index changes of the exciton are calculated for different concentration of magnesium content. The results show that the exciton binding energy is found to exceed LO phonon energy of ZnS for x>0.2 and the incorporation of magnesium ions and the effect of phonon have great influence on the optical properties of ZnS/Zn_1−xMg_xS quantum wells.     

Na-Mg共掺杂ZnO薄膜的结构和光学性质

利用溶胶-凝胶法,在普通载玻片上使用旋转涂膜技术制备了具有c轴择优取向生长的Na-Mg共掺杂的ZnO薄膜。用XRD、SEM、光致发光(PL)及透射光谱对薄膜样品进行了表征。结果表明:Na-Mg共掺杂有利于ZnO薄膜的c轴择优取向生长,并且随着Na+掺杂浓度的增加,晶粒尺寸先增大后减小;通过比较不同掺杂浓度ZnO薄膜的PL谱,推测发光峰值位于380nm的紫外发射与ZnO的自由激子复合有关;发现掺入Mg的确能使ZnO禁带宽度增大,掺杂组分为Na0.04Mg0.2Zn0.76O时,其PL谱只有一个很强的紫光发射峰,其近带边紫外光发射强度较未掺杂的ZnO增强了近10倍,极大地提高了薄膜紫外发光性能;并且随Na+浓度增加薄膜透光性减弱。     

利用脉冲激光沉积法制备高Mg掺杂的六方相MgZnO薄膜

选用Mg0.2Zn0.8O陶瓷靶,利用脉冲激光沉积(PLD)法,在单晶Si(100)和石英衬底上生长了一系列MgZnO薄膜(MZO)。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱(EDS)和紫外可见光透射光谱(UV-Vis)等实验手段,研究了在不同工作压强下生长的薄膜样品的晶体结构、微观形貌和光学性能的变化。结果表明:所有的薄膜样品都是单一的ZnO六方相,禁带宽度随生长压强的升高而增加,变化范围在3.83～4.05eV之间,最短吸收边接近300nm。     

Octaethylporphin films. II absorption and emission of amorphous films

Amorphous thin films octaethylporphin have been prepared and are observed to crystallize over time if thicker than about 100 nm. Transmission spectra of amorphous films have a sharper Soret band than transmission spectra of crystalline films and lack the exciton band seen in crystalline films. The exciton band can be resolved in amorphous films by taking a difference spectrum between two amorphous films of different thickness. Fluorescence is observed from one impurity in amorphous films as compared to two impurities in crystalline films. This indicates a smaller exciton diffusion length in amorphous films as compared to crystalline films, consistent with the differences in the transmission spectra of the two kinds of film.     

Optical properties of MgxZn1−xO thin films deposited on silicon and sapphire substrate by rf magnetron sputtering

The index dispersion at UV–VIS range for polycrystalline Mg_xZn_1−xO films on silicon with different Mg concentration was obtained by spectroscopic ellipsometry (SE) method. It decreases with the increase of the Mg content. Above the relative peak wavelength, they are well fitted by the first-order Sellmeier relation. The band gap of films on sapphire of different Mg content was determined from transmission measurements. Photoluminescence (PL) illustrated that for Mg_xZn_1−xO films every PL peak corresponded to a special excitation wavelength. The wavelength of the PL peak was proportional to the special excitation wavelength. A strong peak was obtained in the blue band for the films due to the large amount of oxygen vacancies caused by excess Zn and Mg atoms, while weak peak at ultraviolet band.     

p型GaN低温粗化提高发光二极管特性

利用金属有机物化学气相沉积技术在蓝宝石衬底上低温生长GaN:Mg薄膜,对不同源流量的GaN:Mg材料特性进行优化研究.研究表明二茂镁(CP2Mg)和三甲基镓(TMGa)物质的量比([CP2Mg]/[TMGa])在1.4×10-3—2.5×10-3范围内,随[CP2Mg]/[TMGa]增加,晶体质量提高,空穴浓度线性增加.当[CP2Mg]/[TMGa]为2.5×10-3时获得空穴浓度与在较高温度生长获得的空穴浓度相当,且薄膜表面较粗糙.采用[CP2Mg]/[TMGa]为2.5×10-3的p型GaN层制备的发光二极管,在注入电流为20mA时,输出光强提高了17.2%.     

Effective barrier height and work function of Mg:Ag thin films with a low Mg concentration acting as cathodes in high-efficiency organic light emitting devices

Organic molecular-beam deposition (OMBD) of Mg:Ag thin films with a low Mg concentration on tris(8-hydroxyquinolino) aluminum (Alq₃) layers at room temperature was performed to investigate the feasibility of using Mg:Ag thin films as cathode electrodes in organic light-emitting devices (OLEDs). The effective barrier height of the Mg:Ag (5:95) thin films grown on the Alq₃ layers, determined from the current-voltage measurements, was as low as 0.22 eV. The work function of the Mg:Ag (5:95) thin film, determined from the secondary electron emission coefficients obtained by using focused ion beam, was 4.12 eV. These results indicate that Mg:Ag (5:95) thin films with a low Mg concentration grown by using the OMBD method hold promise for potential applications as cathode electrodes in high-efficiency OLEDs.     

Optical properties of ZnO thin films on SiO2 substrates deposited by radio frequency magnetron sputtering

The optical properties of both the annealed and as-deposited ZnO thin films by radio frequency (RF)magnetron sputtering on SiO2 substrates were studied. In the annealed films, two pronounced well defined exciton absorption peaks for the A and B excitons were obtained in the absorption spectra, a strong free exciton emission without deep-level emissions was observed in the photoluminescence (PL) spectra at room temperature. It was found that annealing the films in oxygen dramatically improved the optical properties and the quality of the films.     

白宝石衬底上生长的MgxZn1-xO晶体薄膜的结构和光学性能

在白宝石 (sapphire)衬底上低温外延生长出了MgxZn1 -xO晶体薄膜 .x射线衍射 (XRD)及能量色散x射线 (EDX)分析表明 ,MgxZn1 -xO薄膜的晶体结构依赖于薄膜中Mg的组分x,随着Mg组分的增大 ,MgxZn1 -xO薄膜的结构从与ZnO晶体一致的六方结构转变为与MgO晶体一致的立方结构 .对MgxZn1 -xO薄膜的紫外透射光谱及紫外光致荧光谱 (UVPL)的分析表明 ,随着Mg组分的增大 ,光学吸收边产生明显的蓝移 ,表明MgxZn1 -xO晶体薄膜的带隙增大 ,且带隙连续可调 .吸收光谱和XRD测量显示 ,带隙高达 5 6 5eV的MgxZn1 -xO晶体薄膜与MgO之间的晶格失配仅为0 16 % .