离子束溅射自组装Ge/Si量子点生长的演变

采用离子束溅射技术,通过改变Ge的沉积量,在n型Si(100)衬底上自组装生长了一系列Ge量子点样品. 利用AFM和Raman光谱对样品表面形貌和结构进行表征,系统地研究了Ge量子点形貌、密度、尺寸大小以及Ge的结晶性和量子点中组分等随Ge沉积量的演变规律. 结果表明:Ge层从二维薄层向三维岛过渡过程中,没有观察到传统的由金字塔形向圆顶形量子点过渡,而是直接呈圆顶形生长;且随着Ge沉积量的增加,量子点密度先增大后减小,Ge的结晶性增强同时Ge/Si互混加剧,量子点中Si的组分增加. 关键词： 离子束溅射 量子点 表面形貌 Raman光谱     

在Si衬底上自组装生长Ge量子点研究进展

在Si衬底上自组装生长纳米尺度的Ge量子点，由于三维量子限制效应的贡献，能够在能带结构上对Si、Ge天然材料的间接带特性实施准直接带结构的改性，使激子行为和带间复合跃迁得到大幅度增强，同时Ge量子点的可控有序相关排列还有助于发展新一代的Si基电子波量子器件．文章回顾了自20世纪80年代末至今Ge／Si量子点生长研究的重要进展，对其潜在的重要应用作出了评述．结合作者自己的研究结果，着重介绍了Ge量子点的生长动力学及其形态的演变过程，指出自组装生长的Ge／Si量子点属Ⅱ型能带结构，其发光效率比一维量子阱有很大增强．探讨了用模板衬底实现对Ge量子点尺寸和分布的有序可控生长方法与途径．     

Mn离子注入InAs/GaAs量子点结构材料的光电性质研究

用高能离子注入(160keV)的方法对InAs/GaAs量子点结构进行掺杂，研究了不同退火工艺处理后量子点的光致发光和电学性能.相对于长时间退火，快速退火处理后的量子点发光通常较强.在相同的退火条件下，量子点发光峰位随着Mn注入剂量的增加，先是往高能量端快速移动，而后发光峰又往低能方向移动.后者可能是由于Mn原子进入InAs量子点，释放了InAs量子点中的应变所致.对于高注入剂量样品和长时间退火样品，变温电阻曲线在40 K附近会出现反常行为. 关键词： 离子注入 InAs/GaAs量子点 光致发光 团簇     

Si基Ge异质结构发光器件的研究进展

近年来,与Si的CMOS工艺相兼容的Ge/Si异质结构发光器件取得很多重要的进展。本文概述了Si基Ge异质结构发光器件的最新成果,如Ge/Si量子点发光二极管、Si衬底上的Ge发光二极管及激光器和Ge/SiGe多量子阱发光二极管,分别描述了这些器件的特点和增强其发光特性的途径。最后展望了Si基Ge异质结构发光器件的发展趋势,指出尽管Si基Ge异质结构发光器件获得了很大的发展,但是器件的发光效率仍然很低,离实用还有一定距离,还需要在材料和器件的结构方面有更多的创新。     

p型掺杂Si/Ge量子点的电子拉曼散射(英文)

在本文中我们首次报道了p型掺杂的自组织Si/Ge量子点中空穴能级子带间的电子拉曼散射,此电子跃迁的能量为105meV。Si/Ge量子点Ge Ge模的共振拉曼散射表明此空穴能级间的电子拉曼散射与Γ点附近的E0(≈2.52eV)发生了共振,而E1的能量小于2.3eV.变温实验和偏振实验进一步证实了我们的指认。所有观测的实验数据与6 bandk·p能带结构理论的计算结果吻合得很好。     

锗硅量子阱中近带边光跃迁的理论和实验研究

本文研究了SiGe/Si量子阱中近带边光跃迁的产生机制,对由杂质无规分布引起的近带边光跃迁给出了一个物理模型。用此模型计算了光跃迁偶极矩,给出了跃迁偶极矩的上限。提出了未掺杂SiGe/Si量子阱中近带边光跃迁的一种跃迁机制,认为是Ge原子周围波函数畸变的集体行为。用MBE方法生长了掺杂SiGe/Si量子阱材料,在低温下观测到近带边光跃迁。     

小尺寸Si/Ge量子点内应变和组分的拉曼光谱表征

本文详细地研究了原始生长和退火处理后的Si/Ge量子点的拉曼光谱。我们观测到了Si/Ge量子点的一系列本征的拉曼振动模以及Ge-Ge模的LO和TO声子峰间4.2cm-1的频率劈裂。通过这些参数,我们自洽地确定了原始生长的平面直径为20nm和高为2nm的Si/Ge量子点内Ge的平均组分为80%,平均应变为-3.4%。分析清楚地表明了这种小尺寸的Si/Ge量子点内的应变仍遵从双轴应变,并且应变的释放主要由量子点和Si隔离层间Si-Ge原子互扩散决定。     

Si掺杂对AlGaInP/GaInP多量子阱性能的影响

采用LP-MOCVD技术在n-GaAs衬底上生长了AlGaInP／GaInP多量子阱红光LED外延片。以X射线双晶衍射技术和光致发光技术对外延片进行了表征,研究了Si掺杂对AlGaInP／GaInP多量子阱性能的影响。研究表明：掺Si能大大提高(Al0．3Ga0.7)0.5In0.5P／Ga0.5In0.5P多量子阱的发光强度。相对于未故意掺杂的样品,多量子阱垒层掺Si使多量子阱的发光强度提高了13倍,阱层和垒层均掺Si使多量子阱的发光强度提高了28倍。外延片的X射线双晶衍射测试表明,Si掺杂并没有使多量子阱的界面质量变差。     

锡掺杂CsPbBr3量子点的合成及其光电性能研究

采用热注入法合成了锡掺杂CsPbBr_3量子点。透射电子显微镜和X射线衍射仪(XRD)的表征结果显示,少量锡掺杂可以部分替代铅,对量子点有钝化作用,减少了量子点的表面缺陷,提高了量子点的光致发光量子效率(PLQY)。当掺杂铅和锡的物质的量比为9\:1时,量子点的PLQY从未掺杂时的21.0%提高到了40.4%。随着锡掺杂量的增加,XRD谱中出现了杂相,光致发光减弱,PLQY由少量锡掺杂(铅和锡的物质的量比为9\:1)量子点的40.4%降低到CsPb_(0.6)Sn_(0.4)Br_3的10.4%。少量锡掺杂的CsPb_(0.9)Sn_(0.1)Br_3具有最强的光致发光和电致发光,其光致发光峰位为511 nm, PLQY为40.4%,电致发光峰位为512 nm,电致发光亮度为343.0 cd/m~2,是未掺杂CsPbBr_3量子点发光二极管亮度的2.5倍。本实验证明了采用少量锡掺杂CsPbBr_3(CsPb_(0.9)Sn_(0.1)Br_3)可以降低量子点的表面缺陷,提高量子点的光致发光与电致发光性能。     

离子束溅射Ge量子点的应变调制生长

采用离子束溅射技术制备了单层和双层Ge量子点, 通过原子力显微镜对比了不同Si隔离层厚度和不同掩埋量子点密度情况下表层量子点的尺寸和形貌差异, 系统研究了掩埋Ge量子点产生的应变对表层量子点的浸润层及形核的影响, 并用埋置应变模型对其进行解释. 实验结果表明, 覆盖Ge量子点的Si隔离层中分布着的应变场, 导致表层量子点浸润层厚度的降低, 从而增大点的体积; 应变强度随隔离层厚度的减小而增加, 造成表层量子点形状和尺寸的变化; 此外, 应变还调控了表层量子点的空间分布. 关键词： Ge量子点 埋层应变 离子束溅射     

Temperature dependence of photoluminescence from self-organized Ge quantum dots with large size and low density

Photoluminescence(PL) from self-organized Ge quantum dots(QDs) with large size and low density has been investigated over a temperature range from 10 to 300 K using continuous-wave(CW) optical excitation.The integrated PL intensity of QDs observed is negligible at about 10 K and rapidly increases with raising temperature up to 100 K.Through analyzing the PL experimental data of the QDs and wetting layer(WL),we provide direct evidence that there exists a potential barrier,arising from the greater compressive...     

Interband photoconductivity of Ge/Si structures with self-organized quantum rings

At low temperatures a lateral photoconductivity (PC) of Ge/Si (1 0 0) self-organized quantum rings (QRs) structures as a function of interband light intensity has been investigated for different values of lateral voltage and temperature. In contrast to self-organized Ge/Si quantum dots (QDs) structures (grown at the same conditions) where the stepped PC was registered, for QRs structures essential smoothing of PC steps was observed. Such behavior is determined by decreasing of strain potential around QRs in conductive Si matrix due to a transfer of Ge atoms from the center of QDs to its periphery accompanied by Ge/Si intermixing.     

Water‐Dispersible Silicon‐Quantum‐Dot‐Containing Micelles Self‐Assembled from an Amphiphilic Polymer

The dispersion of silicon quantum dots (Si QDs) in water has not been established as well as that in organic solvents. It is now demonstrated that the excellent dispersion of Si QDs in water with photoluminescence (PL) quantum yields (QYs) comparable to those for hydrophobic Si QDs can be realized by combining the processes of hydrosilylation and self‐assembly. Hydrogen‐passivated Si QDs are initially hydrosilylated with 1‐dodecence. The toluene solution of the resulting dodecyl‐passivated Si QDs is mixed with the water solution of the amphiphilic polymer of Pluronic F127 to form an emulsion. Dodecyl‐passivated Si QDs are encapsulated in the micelles self‐assembled from F127 in the emulsion. The size of the Si‐QD‐containing micelles may be tuned in the range from 10 to 100 nm. Although self‐assembly in the emulsion causes the PL QY of Si QDs to decrease, after a few days of storage in ambient conditions, Si QDs encapsulated in the water‐dispersible micelles exhibit recovered PL QYs of ≈24% at the PL wavelength of ≈680 nm. The intensity of the PL from Si QDs encapsulated in the water‐dispersible micelles is >90% of the original value after 60 min ultraviolet illumination, indicating excellent photostability.     

Influence of defects on the optical and structural properties of Ge dots embedded in an Si/Ge superlattice

In this work we studied the influence of high-energy proton irradiation on the optical and structural properties of an Si/Ge superlattice (SL) with embedded Ge quantum dots (QDs). The presence of QDs in the as-grown samples was established by transmission electron microscopy and photoluminescence (PL). The samples were irradiated with 2.0 MeV protons to fluences in the range 2×10¹²-2×10¹⁴ cm^-2. The structural characterization made by X-ray reciprocal space mapping, X-ray reflection and Rutherford backscattering/channelling has shown no changes in the as-grown heterostructure due to the irradiation. In spite of the expected high concentration of nonradiative recombination centres caused by the proton-induced damage, the PL emission from the Ge dots has been observed even for the highest irradiation fluence. The studied QD-in-SL structure has shown an extraordinarily high radiation hardness when compared with previously studied QD heterostructures.     

Near-IR photoluminescence from Si/Ge nanowire-grown silicon wafers: effect of HF treatment

We present the room-temperature near-infrared (NIR) photoluminescence (PL) properties of Si/Ge nanowire (NW)-grown silicon wafers which were treated by vapor of HF:HNO₃ chemical mixture. This treatment activates or enhances the PL intensity in the NIR region ranging from 1000 nm to 1800 nm. The PL consists of a silicon band-edge emission and a broad composite band which is centered at around 1400–1600 nm. The treatment modifies the wafer surface particularly at defect sites especially pits around NWs and NW surfaces by etching and oxidation of Si and Ge. This process can induce spatial confinement of carriers where band-to-band (BB) emission is the dominant property in Si-capped strained Si/Ge NW-grown wafers. Strong signals were observed at sub-band-gap energies in Ge-capped Si/Ge NW-grown wafers. It was found that NIR PL is a competitive property between the Si BB transition and deep-level emission, which is mainly attributable to Si-related defects, Ge dots and strained Ge layers. The enhancement in BB and deep-level PL is discussed in terms of strain, oxygen-related defects, dot formation and carrier-confinement effects. The results demonstrate the effectiveness of this method in enhancing and tuning NIR PL properties for possible applications.     

Photoconductivity of Si/Ge/SiO<Subscript>x</Subscript> and Si/Ge/Si structures with germanium quantum dots

A nonmonotonic dependence of the lateral photoconductivity (PC) on the interband light intensity is observed in Si/Ge/Si and Si/Ge/SiO_x structures with self-organized germanium quantum dots (QDs): in addition to a stepped increase in PC, a stepped decrease in PC is also observed. The effect of temperature and drive field on these features of the PC for both types of structures with a maximum nominal thickness of the Ge layer (N_Ge) is studied. The results obtained are discussed in the context of percolation theory for nonequilibrium carriers localized in different regions of the structure: electrons in the silicon matrix and holes in QDs.     

Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Germanium substrate

We have described Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Ge substrate by MBE. The growth technique includes deposition of a thin germanium buffer layer followed by migration-enhanced epitaxy (MEE) grown GaAs layer at 350°C. The MEE layer was overgrown by a thin low-temperature (475°C) grown GaAs layer with a subsequent deposition of a thick GaAs layer grown at 590°C. The sample was characterized by AFM, cross-sectional TEM and temperature-dependent PL measurements. The AFM shows dense formation of QDs with no undulation in the wetting layer. The XTEM image confirms that the sample is free from structural defects. The 8 K PL emission exhibits a 1051 nm peak, which is similar to the control sample consisting of In(Ga)As/GaAs QDs grown on GaAs substrate, but the observed emission intensity is lower. The similar slopes of Arrhenius plot of the integrated PL intensity for the as-grown QD sample grown on Ge substrate as well as for a reference QD sample grown on GaAs substrate are found to be identical, indicating a similar carrier emission process for both the samples. This in turn indicates coherent formation of QDs on Ge substrate. We presume due to the accumulated strain associated with the self-assembled growth of nanostructures on Ge that nonradiative recombination centers are introduced in the GaAs barrier in between the QD layers, which in turn degrades the overall optical quality of the sample.     

The studies of Ge quantum dots on strained Si0.7Ge0.3 layer by photoluminescence and deep level transient spectroscopy

Systematic studies of Ge quantum dots (QDs) grown on strained Si_0.3Ge_0.7 layer have been carried out by photoluminescence (PL) and deep level transient spectroscopy (DLTS). In PL measurements, two peaks around 0.7 eV are distinguished, which are assigned to two types of QDs observed by atomic force microscopy (AFM). Large blueshifts of the PL peaks from small QDs with the increase of excitation power are observed and attributed to the band bending effects typical for type-II band alignment. From DLTS measurements, the energy levels of holes in both types of QDs are derived, which shift with the change of the number of holes in QDs due to their charge energy. By comparing results from PL and DLTS measurements, further understanding of band alignment with the increase of the number of excitons in QDs is deduced.     

Effect of water and UV passivation on the luminescence of suspensions of silicon quantum dots

This article presents the evolution of the photo-luminescence (PL) of silicon quantum dots (QDs) with an average diameter of 5–6 nm dispersed in alcohol under different conditions. Two samples were considered after alcohol dispersion: freshly synthesized (kept in air for 2 days) QDs which do not exhibit luminescence and air-aged (kept in air for 2 years) QDs exhibiting red-IR luminescence. Experiments performed with addition of a small volume of water, followed by heating for different times showed that the oxidation occurs gradually until transforming totally the initial material in SiO₂. The oxidation process does not enable the appearance of PL from the Si core for dispersed non-aged powders, while it results in a blue shift of the PL maximum intensity for the aged ones. The results obtained after UV illumination clearly indicate an effect of the UV irradiation on the luminescence of QDs dispersed in aqueous environment, and the treatments with acidic water lead to the conclusion of a possible enhancement of the PL by hydrogen passivation of the non-radiative defects. This result should be taken into account for post-production treatments and applications, more particularly, considering a controlled and safe use of luminescent Si QDs.     

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots(QDs) are fabricated on Si nanowires(NWs) substrates with and without Au nanoparticles(NPs). The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence(PL) intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.