Zn1-xMgxO薄膜的光致发光特性研究

采用脉冲激光沉积方法在单晶Si(100)衬底上制备出c轴取向的Zn1-xMgxO单晶薄膜,通过荧光光谱仪研究了薄膜的光致发光特性.实验结果表明,Mg含量增加,Zn1-xMgxO单晶薄膜的紫外发光峰蓝移,发光峰强度减弱,缺陷发光强度增强.同时发现,由于Mg的掺杂,引入了一些束缚能较大的局域束缚态.对于氧气氛下制备的样品,实验发现紫外峰和绿光带发光峰同时增强,但是R值减小,紫外峰红移.对绿光发光机理研究发现,绿光发光带主要与锌空位、氧间隙(Oi)或锌位氧(OZn)等缺陷有关,它是由多个缺陷发光峰组成,各缺陷发光峰强度相对变化导致了绿光发光带的整体移动.     

Photoluminescent analysis of Zn1-xCdxO alloys

The photoluminescent (PL) spectra of Zn_1-xCd_xO (0≤x≤0.53) alloy films were obtained successfully. A new explanation from the viewpoint of band structure is brought forward to comprehend the PL nature of the alloy films. According to this explanation, the near-band-energy emissions of the Zn_1-xCd_xO (x>0) films are caused by the radiative transitions between the Zn4s–Cd5s hybrid level and the O2p level, and the broadenings of the two levels are responsible for the gradually increased line width of the PL peak of the film; Zn3d and Cd4d orbital levels have great effects on the band-gap variations of the alloys. In addition, a quadratic equation is put forward to depict the relationship between the band gaps E_g of the alloys and their Cd contents x, i.e. E_g(x)=3.30-1.22x+1.26x² (0≤x≤0.53). PACS 78.55.-m; 78.55.Et; 81.15.Cd     

Fabrication and Characterization of Well-Aligned Zn1-xMnxO Nanorods

Well-Migned Zn1-xMnxO nanorods have been synthesized successfully on bare silicon substrates by a simple evaporation method without using any catalyst. X-ray diffraction and electron microscopy studies demonstrate that the as-grown nanorods are of single wurtzite phase with a preferential growth direction along their c- axes, Quantitative energy-dispersive spectrum analysis reveals that the concentration of manganese is around 4 at,%, Magnetic measurements show the single-phase Zn1-xMnxO nanorod arrays exhibiting the paramagnetic behaviour. Photolumlnescence spectra demonstrate that the Zn1-xMnxO nanorods preserve ultraviolet emission at room temperature.     

Tuning the magnetic properties of Zn1-xCoxO films

We compare the magnetic properties of two types of Co-doped ZnO films grown on sapphire with distinct structural quality. SQUID magnetometry as well as element-specific synchrotron studies reveal pure paramagnetic behavior for the samples with the highest structural quality, whereas samples with reduced structural quality exhibit superparamagnetic blocking behavior. In this sample signatures of phase separation are detected by X-ray diffraction and X-ray linear dichroism which accounts for the superparamagnetic blocking.     

Zn1-xCdx S合金薄膜的结构和光学性质

采用低压金属有机化学气相沉积(LP-MOCVD)技术,在普通石英衬底上制备出不同Cd组分(0．02,0．44,0．59,0．83,0．91)的Zn1-xCdxS合金薄膜材料。X射线测量表明样品为单一取向的纤锌矿结构,并且随着x的增加衍射峰位基本成线性地从ZnS衍射峰向CdS衍射峰移动。此外,在PL谱中还可以看出随着样品中Cd含量的增加,发光峰从3．66eV红移到2．43eV。根据发光峰位与Zn1-xCdxS中x的变化关系,推导出它们之间的关系近似为Eg(Zn1-xCdxS)=3．61-1．56x 0．38x^2。还探讨了不同Cd组分薄膜材料的X射线衍射峰半峰全宽以及发光峰半峰全宽的变化。     

Low-Temperature Anti-Stokes Luminescence in Zn1-xMgxSe Mixed Crystals

Investigations of photoluminescence and Raman scattering in the ternary Zn_1-xMg_xSe compounds at 4.2 K were performed both in the Stokes and anti-Stokes regions using cw laser excitation with various wavelengths within the transparency band of the crystals. The anti-Stokes luminescence was observed for the first time in the ternary Zn_1-xMg_xSe compounds. We have found variations in the shape and position of the Stokes and anti-Stokes luminescence bands with an increase in the band gap energy, which depends on magnesium content. We assume that the anti-Stokes emission is generated by two-step excitation via deep-level centers. It is shown that the low-temperature anti-Stokes photoluminescence can probe the spatial distribution profiles of impurities in the bulk of crystals.     

半磁半导体Zn1-xMnxS中的能量传递

本文测量了Zn1-xMnxS在不同Mn浓度(0.001x=0.062,T=80K时的Zn1-xMnxS的发射谱及其衰减曲线,得到两个衰减寿命:τ1=70μs,τ2>1000μs,这表明在高Mn浓度时存在着两个弛豫过程:一个是较快的,另一个则是较慢的,根据Goede等人的实验结果可以断定较慢的过程来自孤立的Mn2-离子,那么便可以判知较快的过程是来源于Mn2-离子对.正是高Mn浓度下的Zn1-xMnxS中存在着Mn2+-Mn2+离子对,在其间有能量迁移以及它和能量受主之间的能量传递造成了该体系中的IR发射.     

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.     

Quasiparticle lifetimes due to A1 impurities in Zn

We have calculated the quasiparticle lifetimes due to Al impurities in Zn. For the Zn electronic structure we use the wave functions, Fermi velocities and surface elements calculated by Tomlinson and Swihart who based their work on the accurate pseudopotential fit to the de Haas-van Alphen data obtained by Stark and Falicov. The impurity pseudopotential form factor is obtained from the procedure developed by Shaw.     

Optical absorption in cubic Zn1-xMnxSe under hydrostatic pressure

The optical absorption edges of the diluted magnetic semiconductors Zn_1-xMn_xSe have been measured under hydrostatic pressure for x ≦ 0.25. We found a blue shift of the direct interband gap with pressure which is nearly independent of the manganese concentration. An absorption band at 2.62 eV is assigned to the intra-atomic transition ⁶A₁ → ⁴A₁, ⁴E of the manganese ions. Its pressure shift indicates an increase of the d-p-hybridization which is, however, weaker than in the tellurides. Additional bands appear at sufficiently high pressures in samples with x = 0.15 and 0.25.     

燃烧反应法制备纳米Zn1-xNixO粉体

采用燃烧反应法制备了纳米Zn1-xNixO粉体。结果表明,当Ni掺杂量增加到x=0.010时,样品中不仅部分Ni2+取代了Zn2+,还出现了立方NiO;通过FTIR发现样品在1041.68cm-1附近出现了一个新的吸收带,表现出良好的红外吸收特性。     

Intra-manganese absorption and luminescence in Zn1-xMnxSe semimagnetic semiconductor

Optical absorption and luminescence of Zn_1-xMn_xSe (0 < x < 0.53) is measured at T = 10, 77 and 300 K below fundamental absorption edge. Three absorption and one luminescence bands are observed and are attributed to the intra-ion transitions of Mn²⁺ in 3d⁵ configuration. Crystal field parameter Dq and Racah parameters B and C are derived as well as stabilization energy.