H2O2催化多孔硅的光致发光研究

采用H2O2催化的电化学法制备多孔硅,用原子力显微镜观察了样品的形貌,并测量了在不同电流密度下制得的多孔硅和在不同氧化时间高温氧化的多孔硅的光致发光谱。实验结果表明,采用H2O2催化的电化学法制备的多孔硅与常规电化学法制备的多孔硅相比,其表面更平整、细密、均匀。随着电流密度和氧化时间的增加,多孔硅的发光谱峰位蓝移。此实验结果符合量子限制模型。     

多孔Si/纳米ZnS复合材料发光的研究

利用脉冲激光沉积(PLD)分别在Si片和多孔Si衬底上沉积了ZnS薄膜,考察衬底对ZnS薄膜结构和发光性能的影响。X射线衍射(XRD)和扫描电镜(SEM)测量表明,两种衬底上制备的ZnS薄膜均沿立方相结构β-ZnS(111)晶向择优取向生长。多孔Si衬底上生长的ZnS薄膜表面有很多凹坑,而Si衬底上生长的ZnS薄膜表面相对比较平整。光致发光(PL)谱显示,ZnS薄膜沉积后,多孔Si的发光峰强度减小且峰位发生蓝移。根据ZnS薄膜具有较高透射率的特点,把透射出ZnS的多孔Si的橙红光和ZnS的发光叠加,多孔Si/ZnS纳米薄膜复合体系在可见光区有很强的PL现象。     

氧与激光辐照对多孔硅光致发光光谱的影响

将化学腐蚀后的多孔硅样品分别置于大气和氧气中,用激光连续辐照其表面.观察到多孔硅的光致发光光谱峰位随辐照时间增加发生蓝移,最后达到稳定,在真空中作同样处理的多孔硅光致发光峰位却没有移动.X射线光电子谱测量结果表明,在大气及氧气中激光辐照的多孔硅层内并未探测到二氧化硅,结合红外吸收光谱实验,认为蓝移的原因可能是氧置换了多孔硅内表面的硅,出现Si-O-Si结构的结果.     

纳米非晶硅薄膜的界面发光特性

采用螺旋波等离子体增强化学气相沉积(HWP-CVD)技术沉积了不同氢稀释比的富硅氢化非晶氮化硅(a-SiNxH)薄膜,并利用光致发光(PL)和光致发光激发(PLE)谱技术对其发光特性进行了研究.结果显示,所有样品发光均表现为两个带的叠加一个发光带随氢稀释比增大而发生蓝移,另一个发光带则固定在2.9eV左右.前者关联于镶嵌在a-SiNxH基质内非晶纳米硅颗粒的界面发光,后者来源于a-SiNxH基质相关的局域态中电子和空穴对的辐射复合.并结合所沉积薄膜的吸收特性,分析了缺陷态和界面态对薄膜中非晶纳米硅界面发光特性的影响.     

纳米多孔氧化硅的制备及荧光光谱研究

为了制作性能良好的光电子集成、光波导等器件,研究纳米多孔氧化硅膜的制备和表征具有重要意义。采用高温氧化多孔硅的方法制备了纳米多孔氧化硅,进行了两种样品的荧光光谱和傅里叶变换红外吸收谱对比检测。相比于多孔硅,多孔氧化硅的发光峰值向短波方向"蓝移"并且发光强度明显降低。多孔硅表面基本是由氢饱和的,而经氧化后的多孔氧化硅表面的Si—H键大部分被Si—O键所代替。结果表明,量子限制效应是样品的荧光光谱"蓝移"的原因,而发光强度的降低则归因于样品表面辐射复合中心的减少和内部纳米硅柱(硅晶粒)尺寸的减小。     

纳米非晶硅薄膜的界面发光特性

采用螺旋波等离子体增强化学气相沉积(HWP-CVD)技术沉积了不同氢稀释比的富硅氢化非晶氮化硅(a-SiNx:H)薄膜,并利用光致发光(PL)和光致发光激发(PLE)谱技术对其发光特性进行了研究.结果显示,所有样品发光均表现为两个带的叠加:一个发光带随氢稀释比增大而发生蓝移,另一个发光带则固定在2.9eV左右.前者关联于镶嵌在a-SiNx:H基质内非晶纳米硅颗粒的界面发光,后者来源于a-SiNx:H基质相关的局域态中电子和空穴对的辐射复合.并结合所沉积薄膜的吸收特性,分析了缺陷态和界面态对薄膜中非晶纳米硅界面发光特性的影响.     

多孔硅发光峰位波长为370nm的紫外光发射

对特定工艺制备的多孔硅进行干氧氧化处理，观察到光致发光峰位波长为３７０ｎｍ左右的紫外光发射．紫外光强度与高温氧化温度有关，当氧化温度为１０００℃时，多孔硅紫外光发射最强，而在１１５０℃温度下氧化５ｍｉｎ，多孔硅纳米硅粒消失后，紫外发射变得很弱．紫外光峰位与氧化温度无关，但在１０００℃氧化的多孔硅光致发光谱中出现附加的位干３６０ｎｍ的发光峰．如认为光激发主要发生在多孔硅的纳米硅粒中，而光发射主要发生在多孔硅中包裹纳米硅的ＳｉＯｘ层中的两种（或多种）发光中心上，则本文的实验能被很好解释．     

多孔硅PL谱的影响因素分析

通过阳极氧化电化学方法制备了多孔硅,并在室温下对不同条件下制得的多孔硅光致发光谱(PL谱)进行系统的分析.结果表明,随着阳极电流密度、阳极化溶液浓度和时间的增大,多孔硅的PL谱峰将发生"蓝移",并且PL峰强也显著增加,但过大的电流密度、阳极化溶液浓度和时间将导致PL峰强下降.另外,还发现PL谱存在多峰结构,而多孔硅在空气中放置时间的延长将引起其PL的短波峰"蓝移"和强度下降,但对长波峰只引起强度减弱,并不影响其峰位.PL谱的多峰结构可以认为是由于样品中同时存在"树枝"状和"海绵"状两种微观结构所产生的,在这个假设下,用多孔硅氧化后发光中心从硅表面移到二氧化硅层及量子限制模型能够解释上述现象.     

多孔硅PL谱的影响因素分析

通过阳极氧化电化学方法制备了多孔硅,并在室温下对不同条件下制得的多孔硅光致发光谱(PL谱)进行系统的分析.结果表明,随着阳极电流密度、阳极化溶液浓度和时间的增大,多孔硅的PL谱峰将发生"蓝移",并且PL峰强也显著增加,但过大的电流密度、阳极化溶液浓度和时间将导致PL峰强下降.另外,还发现PL谱存在多峰结构,而多孔硅在空气中放置时间的延长将引起其PL的短波峰"蓝移"和强度下降,但对长波峰只引起强度减弱,并不影响其峰位.PL谱的多峰结构可以认为是由于样品中同时存在"树枝"状和"海绵"状两种微观结构所产生的,在这个假设下,用多孔硅氧化后发光中心从硅表面移到二氧化硅层及量子限制模型能够解释上述现象.     

Si基热氧化Si1-x-yGexCy薄膜的室温光致发光特性

采用等离子体增强化学气相淀积(PECVD)法在Si(100)衬底上淀积一层厚度约为170nm的富Ge高C含量的Si1-x-yGex/Cy薄膜,然后将其分别在800℃和1100℃下湿氧氧化20min.在室温下观测到强烈的光致发光.室温下的光致发光谱(PL谱)测量显示,800℃下氧化后的样品在370nm和396nm附近有两个光致发光带,1100℃下氧化后的样品只在396nm附近有一个光致发光带.396nm附近的发光带可归之于由氧化薄膜中的缺陷O-Si-O(Si20)或O-Ge-O(Ge20)引起的,而370nm附近的发光带与薄膜中Ge-C对发光中心有关.     

Optical properties of boron modulation-doped SiGe quantum wells and Si thin films

Effects of modulation doping on the radiative recombination in Si thin films and SiGe quantum wells (QWs) grown by molecular beam epitaxy are studied in details by photoluminescence (PL) spectroscopy. It is shown that the formation of a two-dimensional hole gas, either in the SiGe QWs or in the doping-induced notch potential in Si thin films, manifests itself in the appearance of characteristic broad luminescence bands. The PL properties are found to be strongly dependent on structure parameters as well as on the experimental conditions, such as photo-excitation intensity and measurement temperature. In the modulation doped SiGe QWs the recombination process is shown to be strongly affected by correlation phenomena, such as Fermi edge singularity.     

The effect of copper doping of n-ZnSe crystals on the structure of luminescence centers of long-wavelength luminescence

The photoluminescence and luminescence excitation spectra of copper-doped n-ZnSe crystals were investigated in the temperature range 77–400 K during diffusion of the copper into the crystal from the liquid, gas, and and solid phases. It is shown that the structure of the associative centers responsible for emission in the red and green regions of the spectrum depends on the method of copper doping. It is established that during the interphase interaction on the (ZnSe crystal)-(copper film) boundary, zinc atoms dissolve in the copper film and the copper atoms diffuse into the zinc selenide crystal. Fiz. Tekh. Poluprovodn. 32, 171–177 (February 1998)     

Specific features of photoluminescence properties of copper-doped cadmium selenide quantum dots

The effect of doping with copper on the photoluminescence properties of cadmium selenide quantum dots 4 nm in dimension is studied. The quenching of the excitonic photoluminescence band related to the quantum dots and the appearance of an impurity photoluminescence band in the near-infrared region are observed after doping of the quantum dots with copper. It is established that, on doping of the quantum dots, the photoluminescence kinetics undergoes substantial changes. The photoluminescence kinetics of the undoped quantum dots is adequately described by a sum of exponential relaxation relations, whereas the photoluminescence kinetics experimentally observed in the region of the impurity band of the copper-doped samples follows stretched exponential decay, with the average lifetimes 0.3–0.6 μs at the photon energies in the range of 1.47–1.82 eV. The experimentally observed changes in the photoluminescence properties are attributed to transformation of radiative centers in the quantum dots when doped with copper atoms.     

Photoluminescence Characterization of Boron-doped Si Layers Grown by Molecular Beam Epitaxy

Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900 ℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band（from 0.75 eV to 0. 90 eV） including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.     

Molecular Self‐Doping Controls Luminescence of Pure Organic Single Crystals

Organic optoelectronics calls for materials combining bright luminescence and efficient charge transport. The former is readily achieved in isolated molecules, while the latter requires strong molecular aggregation, which usually quenches luminescence. This hurdle is generally resolved by doping the host material with highly luminescent molecules collecting the excitation energy from the host. Here, a novel concept of molecular self‐doping is introduced in which a higher luminescent dopant emerges as a minute‐amount byproduct during the host material synthesis. As a one‐stage process, self‐doping is more advantageous than widely used external doping. The concept is proved on thiophene–phenylene cooligomers (TPCO) consisting of four (host) and six (dopant) conjugated rings. It is shown that <1% self‐doping doubles the photoluminescence in the TPCO single crystals, while not affecting much their charge transport properties. The Monte‐Carlo modeling of photoluminescence dynamics reveals that host–dopant energy transfer is controlled by both excitonic transport in the host and host–dopant Förster resonant energy transfer. The self‐doping concept is further broadened to a variety of conjugated oligomers synthesized via Suzuki, Kumada, and Stille crosscoupling reactions. It is concluded that self‐doping combined with improved excitonic transport and host–dopant energy transfer is a promising route to highly luminescent semiconducting organic single crystals for optoelectronics.     

Photoluminescence properties of GaN with dislocations induced by plastic deformation

Fresh (a/3)[1120] dislocations on the (1100) prismatic plane were introduced into GaN bulk crystals by plastic deformation at 950–1000°C. In photoluminescence studies at 11 K, the near-band-edge (3.48 eV) luminescence intensity decreased remarkably in the deformed GaN, which was attributed to the introduction of high-density nonradiative recombination centers during plastic deformation. The yellow-band luminescence (2.22 eV) decreased due to plastic deformation, while several luminescence bands centered at 1.79, 1.92, and 2.4 eV developed. The dependence of PL features on deformation and annealing suggests that yellow luminescence is not related to the native structure of edge dislocations in GaN.     

Defect-related luminescence of GaN:Zn films thermally treated in a radio-frequency ammonia plasma

The effect of thermal annealing in nitrogen radicals obtained by the treatment of NH₃ in a radio-frequency discharge on the luminescence properties of GaN:Zn films grown by MOCVD/hydride epitaxy on sapphire (0001) substrates is investigated. As the thermal treatment temperature was increased, a steady weakening of the violet (2.88 eV) and near-edge (3.48 eV) photoluminescence bands was observed. As a result of the thermal treatment in nitrogen radicals at 500–750°C, new bands that peaked at 3.27 and 3.42 eV were detected; the intensities of these bands increased with increasing treatment temperature. The mechanism of formation and the origin of all the bands are analyzed comprehensively. It is found that the luminescence bands at 2.88, 3.42, and 3.27 eV are characteristic of the GaN films obtained by practically each technology and are associated with the simple structural defects. The participation of O in the formation of the band at 3.42 eV is proved experimentally.     

Investigation of structural,optical and morphological properties of copper doped zinc sulphide nanoparticles

Semiconductor nanoparticles doped with transition metal ions can influence the transition probabilities and electronic structure. The undoped and copper doped zinc sulphide nanoparticles with various concentrations are synthesized by wet chemical co-precipitation method. These nanoparticles are characterized by using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), UV–visible (UV–vis) absorption spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy, conductivity measurement and time-resolved photoluminescence studies. X-ray powder diffraction analysis reveals that the synthesized samples have cubic zinc blende structure. The Scanning Electron Microscope shows the synthesized nanoparticles are agglomerated. The UV–visible spectra reveal the absorption edge is red shifted. The FT-IR spectra show vibrational peaks around 617 cm⁻¹ which indicate the presence of Cu–S stretching modes. The AC conductivity measurement confirms the semiconducting nature and shows a marked increase in conductivity as the doping concentration of copper increases. The photoluminescence shows that the emission at 426 nm may be due to transition from the conduction band to the zinc vacancies. These transition metal ions doped semiconductor nanoparticles have important applications in solid state lighting, imaging, and other photonic devices.     

Ultraviolet luminescence of thin GaN films grown by radical-beam gettering epitaxy on porous GaAs(111) substrates

GaN films with a thickness of 0.1 μm were grown by radical-beam gettering epitaxy on porous GaAs(111) substrates. Excitonic luminescence bands are dominant in the photoluminescence spectra measured at 4.2 K. The energy positions of excitonic-band peaks are analyzed; as a result, it is concluded that there are stresses in the grown GaN films. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 11, 2003, pp. 1303–1304. Original Russian Text Copyright ? 2003 by Kidalov, Sukach, Revenko, Potapenko.     

半导体硅上激光诱导选择性化学镀铜

利用YAG脉冲激光在n型硅基底上制备出了铜化学镀薄层,由激光剥离形成的微型图元通过化学镀铜工艺在硅基底上形成铜的微型结构。在化学镀工艺过程中为了使得化学镀铜沉积能够连续进行,要对基底表面先进行活化。实验表明,预处理及其后的清洗工艺对选择性镀膜质量影响很大;采用丙酮或硝酸水清洗,有助于获得清晰的微型图元结构。