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1.
We investigate the annealing behavior of InAs layers with different thicknesses in a GaAs matrix. The diffusion enhancement by strain, which is well established in strained quantum wells, occurs in InAs/GaAs quantum dots (QDs). A shift of the QD luminescence peak toward higher energies results from this enhanced diffusion. In the case of structures where a significant portion of the strain is relaxed by dislocations, the interdiffusion becomes negligible, and there is a propensity to generate additional dislocations. This results in a decrease of the QD luminescence intensity, and the QD peak energy is weakly affected.  相似文献   

2.
Vertically stacked layer structure is useful for controlling the size distribution of quantum dots. The dependence of the size distribution of quantum dots on the stacking numbers is theoretically and experimentally investigated. We show that the size distribution of quantum dots decreases with increasing the stacking number, and it occurs drastically when the stacking number is changed from 1 to 2. The quantitative analysis on in-plane strain energy distribution is also performed for the explanation.  相似文献   

3.
The effect of pulsed laser annealing (PLA), using an excimer laser, on the luminescence efficiency of self-organized InAs/GaAs and In0.4Ga0.6As/GaAs quantum dots has been investigated. It is found that such annealing can enhance both the peak and integrated photoluminescence (PL) efficiency of the dots, up to a factor of 5–10 compared to as-grown samples, without any spectral shift of the luminescence spectrum. The improved luminescence is attributed to the annealing of nonradiative point and extended defects in and around the dots.  相似文献   

4.
Self-organized InGaAs/GaAs quantum dots (QDs) stacked multilayers have been prepared by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy shows that the InGaAs QDs are nearly perfectly vertically aligned in the growth direction [100]. The filtering effect on the QDs distribution is found to be the dominant mechanism leading to vertical alignment and a highly uniform size distribution. Moreover, we observe a distinct infrared absorption from the sample in the range of 8.6–10.7 μm. This indicates the potential of QDs multilayer structure for use as infrared photodetector.  相似文献   

5.
In the present work, we report on the investigation of a p-n heterostructure with InAs/GaAs quantum dots (QD) by capacitance-voltage and deep level transient spectroscopy. We have observed controllable and reversible metastable population of the energy states of quantum dots and interface in the structure containing one plane of InAs QDs as a function of temperature of isochronous annealing as well as under bias-on-bias-off cooling conditions and white light illumination. This effect was attributed to the change in the Fermi level position due to the hole capture on self-trapped defects similar to the DX center in GaAs after isochronous annealing and white light illumination.  相似文献   

6.
Vertical ordering in stacked layers of InAs/GaAs quantum dots is currently the focus of scientific research because of its potential for optoelectronics applications. Transmission electron microscopy was applied to study InAs/GaAs stacked layers grown by molecular-beam-epitaxy with various thicknesses of GaAs spacer. Thickness dependencies of quantum dot size and their ordering were observed experimentally and, then, compared with the results of strain calculations based on the finite element method. The vertical ordering did occur when the thickness of the GaAs spacer was comparable with the dot height. The ordering was found to be associated with relatively large InAs dots on the first layer. Quantum dots tend to become larger in size and more regular in plane with increasing numbers of stacks. Our results suggest that the vertical ordering is not only affected by strain from the InAs dots on the lower layer, but by total strain configuration in the multi-stacked structure.  相似文献   

7.
InAs/GaAs量子点材料和激光器   总被引:2,自引:0,他引:2  
吴巨  王占国 《微纳电子技术》2005,42(11):489-494
介绍了近年来长波长InAsG/aAs量子点材料的生长、结构性质和量子点激光器的研究进展。  相似文献   

8.
利用固态源分子束外延技术,按S-K模式生长出五层堆垛InAs/GaAs量子点(QD)微结构材料. 用这种QD材料制成的激光器,内光学损耗为2.1cm-1,透明电流密度为15±10 A/cm2. 对于条宽100μm,腔长2.4mm的激光器(腔面未经镀膜处理),室温下基态激射的波长为108μm,阈值电流密度为144A/cm2,连续波光功率输出达2.67W(双面),外量子效率为63%,特征温度为320K. 研究了QD激光器翟激射特性,并对结果作了讨论.  相似文献   

9.
The time-resolved photoluminescence and steady photoluminescence (TRPL and PL) spectra on self-assembled InAs/GaAs quantum dots (QDs) are investigated. By depositing GaAs/InAs short period superlattices (SLs), 1. 48μm emission is obtained at room temperature. Temperature dependent PL measurements show that the PL intensity of the emission is very steady. It decays only to half as the temperature increases from 15 K to room temperature, while at the same time, the intensity of the other emission decreases by a factor of 5 orders of magnitude. These two emissions are attributed to large-size QDs and short period superlattices (SLs), respectively. Large-size QDs are easier to capture and confine carriers, which benefits the lifetime of PL, and therefore makes the emission intensity insensitive to the temperature.  相似文献   

10.
In this article, recent investigations of vertically aligned quantum dot columns conducted at Stanford University are reviewed. The quantum dots are InAs in a matrix of GaAs. Both the quantum dots and quantum dot columns are formed through strain-induced islanding, without lithography. Two aspects of these columns are discussed. First, the electronic coupling of quantum dots within columns of up to ten quantum dots is demonstrated. The coupling is adjusted and improvements to a simple light-emitting diode are shown. Second, increased uniformity of a surface quantum dot layer is shown when a subsurface layer of these columns are used. The most impressive results occur when the columns contain a large number of islands. Reduced variations in average ensemble height and diameter, called size uniformity, and average nearest neighbor distances, called structural uniformity, are shown. A surface unit cell of islands is demonstrated and the lack of a surface lattice is discussed.  相似文献   

11.
InAs/GaAs自组装量子点结构的能带不连续量   总被引:2,自引:2,他引:0  
为确定异质结界面带阶,结合光致发光(PL)谱和深能级瞬态谱(DLTS)测量结果,利用有效质量近似理论,计算得到了InAs/GaAs自组装量子点结构的能带不连续量,其中导带不连续量ΔEc=0.97 eV,价带不连续量ΔEv=0.14 eV.  相似文献   

12.
系统研究了InAlAs/InGaAs复合限制层对InAs量子点光学性质的影响;发现InAs量子点的基态发光峰位、半高宽以及基态与第一激发态的能级间距都强烈地依赖于InAlAs薄层的厚度和In的组分;得到了室温发光波长在1.35μm,基态与第一激发态的能级间距高达103 meV的InAs量子点的发光特性。这一结果对实现高T_0的长波长InAs量子点激光器的室温激射具有重要意义。  相似文献   

13.
Structures with vertically correlated self-organised InAs quantum dots (QDs) in a GaAs matrix were grown by the low-pressure metal-organic vapour phase epitaxy (MOVPE) and characterised by different microscopic techniques. Photoluminescence in combination with photomodulated reflectance spectroscopy were applied for characterisation of QDs structures. We show that combination of both methods allows detecting optical transitions originating both from QDs and wetting (separation) layers, which can be than compared with those obtained from numerical simulations. On the basis of obtained results, we demonstrate that photoreflectance spectroscopy is an excellent tool for characterisation of QDs structures wetting layers and for identification of spacer thicknesses in vertically stacked QDs structures.  相似文献   

14.
A site-control technique for individual InAs quantum dots (QDs) has been developed by using scanning tunneling microscope (STM) probe-assisted nanolithography and self-organizing molecular-beam epitaxy. We find that nano-scale deposits can be created on a GaAs surface by applying voltage and current pulses between the surface and a tungsten tip of the STM, and that they act as “nano-masks” on which GaAs does not grow directly. Accordingly, subsequent thin GaAs growth produces GaAs nano-holes above the deposits. When InAs is supplied on this surface, QDs are self-organized at the hole sites, while hardly any undesirable Stranski-Krastanov QDs are formed in the flat surface region. Using this technique with nanometer precision, a QD pair with 45-nm pitch is successfully fabricated. An erratum to this article is available at .  相似文献   

15.
We investigated the change in the structural and optical properties of InAs/InP quantum structures during growth interruption (GI) for various times and under various atmospheres in metalorganic chemical vapor deposition. Under AsH3 + H2 atmosphere, the mass transport for the 2D-to-3D transition was observed during the GI. Photoluminescence peaks from both quantum dots (QDs) and quantum wells were observed from the premature QD samples. The fully developed QDs showed the two distinct temperature regimes in the PL peak position, full width at half maximum (FWHM) and wavelength-integrated peak intensity. The two characteristic activation energies were obtained from the InAs/InP QDs: ∼10 meV for intra-dot excitation and 90 ∼ 110 meV for the excitation out of the dots, respectively. It was also observed that the QD evolution kinetics could be suppressed in PH3 + H2 and H2 atmospheres. The proper control of GI time and atmosphere might be a useful tool to further improve the properties of QDs.  相似文献   

16.
A number of nano-engineering methods are proposed and tested to improve optical properties of a laser gain medium using the self-assembled InAs quantum dot (QD) ensemble. The laser characteristics of concern include higher gain, larger modulation bandwidth, higher efficiency at elevated temperatures, higher thermal stability, and enhanced reliability. The focus of this paper is on the management of QD properties through design and molecular beam epitaxial growth and modification of QD heterostructures. This includes digital alloys as high-quality wide-bandgap barrier; under- and overlayers with various compositions to control the dynamics of QD formation and evolution on the surface; shape engineering of QDs to improve electron-hole overlap and reduce inhomogeneous broadening; band engineering of QD heterostructures to enhance the carrier localization by reduction of thermal escape from dots; as well as tunnel injection from quantum wells (QWs) to accelerate carrier transfer to the lasing state. Beneficial properties of the developed QD media are demonstrated at room temperature in laser diodes with unsurpassed thermal stability with a characteristic temperature of 380 K, high waveguide modal gain >50 cm−1, unsurpassed defect tolerance over two orders of magnitude higher than that of QWs typically used in lasers, and efficient emission from a two-dimensional (2-D) photonic crystal nanocavity.  相似文献   

17.
Self-assembled InAs quantum dots with graded composition strain-reducing layer (SRL) grown on exact substrates were studied. It is shown that a graded InxGa1-xAs SRL leads to growth quality improvement, emission efficiency enhancement, and wavelength blueshift. Samples grown on 2° misoriented substrates with different In contents in graded InxGa1-xAs SRL were also investigated, and emission efficiency enhancement and wavelength blueshift were found when graded SRL was introduced and when the change rate of In content in graded InxGa1-xAs SRL was enlarged.  相似文献   

18.
用低温光荧光(PL)和透射电子显微镜(TEM)研究了表面氮化自组织InAs/GaAs量子点的光学性能和微观结构。结果表明氮化后形成薄层的InAsN薄膜作为应变缓和层覆盖在量子点的表面,使得随着氮化时间的增加,InAs量子点的位错密度提高、尺寸变大、纵横比提高、发光波长变长、强度变低。  相似文献   

19.
基于石墨烯/铟砷量子点/砷化镓异质结新型光电探测器   总被引:1,自引:1,他引:0  
研究了一种石墨烯/铟砷量子点/砷化镓界面形成的异质结探测器的暗电流特性以及光电响应性质.虽然石墨烯具有很高的电子迁移率,但受限于较低的光子吸收率,使其在光电探测领域的应用受到了限制.而半导体量子点具有量子效率高,光吸收能力强等独特优点.于是利用石墨烯-砷化铟量子点-砷化镓异质结结构制备了一种新型光电探测器.并对该探测器的响应率、I-V特性曲线、暗电流特性、探测率、开关比等关键性能进行了研究.其在637 nm入射光情况下的响应率、探测率以及开关比可分别达到为17. 0 m A/W、2. 3×10~(10)cm Hz~(1/2)W~(-1)和1×10~3.而当入射光为近红外波段的940纳米时,响应率进一步增加到了207 m A/W.同时,还证实了该器件的暗电流、肖特基势垒高度和理想因子对温度的都具有较高的依赖性都较强.  相似文献   

20.
Cu掺杂对ZnO量子点光致发光的影响   总被引:1,自引:0,他引:1  
徐建萍 《光电子.激光》2010,(11):1593-1596
通过溶液法合成了Cu掺杂ZnO量子点。X射线衍射(XRD)和高分辨电子透射电镜(HRTEM)图像显示Cu掺杂ZnO量子点具有六角纤锌矿结构,晶粒大小为4~5nm。Cu掺杂抑制了ZnO量子点颗粒长大。室温光致发光(PL)谱观察到紫外带边和可见区两个发射峰。随着Cu掺杂浓度的增大,紫外荧光峰位发生缓慢红移,由366nm移到370nm;可见区发射峰位发生蓝移,由525nm移到495nm;同时,两个发射峰强度降低。光谱结果表明:Cu的掺入,一方面抑制表面与O空位有关的缺陷,在495nm出现了与Cu1+有关的发射峰;另一方面,Cu离子掺入ZnO量子点引入一些非辐射中心,降低了自由激子发射。  相似文献   

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