Spatial ordering of self-organized InGaAs/AlGaAs quantum disks on GaAs (311)B substrates

We report the control of self-organization of In_xGa_1−xAs/AlGaAs quantum disks on GaAs (311)B surfaces using a novel technique based upon lithography-defined SiN dot arrays. A strained InGaAs island array selectively grown using the SiN dots provides periodic strain field. When the pitch of lateral ordering corresponds with the period of the strain field, self-organized quantum disks stacked on the InGaAs islands are precisely arranged just as the buried SiN dot array. The spacing of the array element is 250–300 nm (x = 0.3) and around 150 nm (x = 0.4). Vertical alignment by strain is achieved at a very thick (95 nm) separating layer. Characterization using atomic force microscopy reveals the size-fluctuation of disk is dramatically improved with spatial ordering.     

Determination of the minimum island size for full exciton localization due to thickness fluctuations in Zn1−xCdxSe quantum wells

Fluctuations of the thickness of quantum wells (QWs) of few monolayers are one of the causes of exciton localization. Here, we present the results of the determination of the minimum lateral dimensions of islands produced by thickness fluctuations in Zn_1−xCd_xSe QWs, which cause full exciton localization. We have calculated the localization energy of excitons in the frame of the factorized-envelope approximation. We found that the excitons are well localized in the islands of the QW when their lateral dimensions are larger than ∼15 times the exciton Bohr radius.     

Nonlinear Optical Properties of CdS/ZnS Quantum Dots in a High-Molecular-Weight Polyvinylpyrrolidone Matrix

Sols containing core/shell CdS/ZnS semiconductor quantum dots are synthesized and their nonlinear properties, which are interesting for a large variety of applications in nanophotonics, are studied. The quantum dots produced are smaller in dimensions than the exciton Bohr radius and, therefore, exhibit a well-pronounced quantum-confinement effect. The nonlinear optical properties of low-concentration sols are studied upon exposure to laser pulses with an emission wavelength of 532 nm and a duration of 5 ns by the z-scan technique. The dependences of nonlinear optical coefficients on the concentration of CdS/ZnS quantum dots are obtained. The intensity dependence of two-photon absorption coefficients is presented. The dependence determines the boundary of the influence of high-order nonlinearities on the nonlinear transmittance of the samples. The mechanisms of optical limitation exhibited by sols, specifically, two-photon absorption, nonlinear refraction, and nonlinear scattering are discussed.     

Broadband tuning (170 nm) of InGaAs quantum well lasers

The wavelength tuning properties of strained InGaAs quantum well lasers using an external grating for feedback is reported. Tunable laser oscillation has been observed over a range of 170 nm, between 840 and 1010 nm, under pulsed current excitation. The optimal conditions for broadband tunability for the InGaAs lasers are different from GaAs lasers, which is attributed to a difference in spectral gain curves. Together with an optimised GaAs quantum well laser the entire region between 740 and 1010 nm is spanned.<>     

Optical properties of InGaAs/InGaAlAs quantum wells for the 1520–1580 nm spectral range

The optical properties of elastically strained semiconductor heterostructures with InGaAs/InGaAlAs quantum wells (QWs), intended for use in the formation of the active region of lasers emitting in the spectral range 1520–1580 nm, are studied. Active regions with varied lattice mismatch between the InGaAs QWs and the InP substrate are fabricated by molecular beam epitaxy. The maximum lattice mismatch for the InGaAs QWs is +2%. The optical properties of the elastically strained InGaAlAs/InGaAs/InP heterostructures are studied by the photoluminescence method in the temperature range from 20 to 140°C at various power densities of the excitation laser. Investigation of the optical properties of InGaAlAs/InGaAs/InP experimental samples confirms the feasibility of using the developed elastically strained heterostructures for the fabrication of active regions for laser diodes with high temperature stability.     

InGaAs/GaAs/AlGaAs应变量子阱激光器

优化设计了既能实现较小垂直方向远场发散角,又能降低腔面光功率密度的ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变层量子阱激光器,并计算了该结构激光器实现基横模工作的脊形波导结构参数。利用分子束外延生长了ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变量子阱激光器材料并研制出基横模输出功率大于１４０ｍＷ,激射波长为９８０ｎｍ的脊形波导应变量子阱激光器,其微分量子效率为０．８Ｗ／Ａ,垂直和平行结平面方向远场发散角分别为２８°和６．８°     

快速热退火对高应变InGaAs/Ga As量子阱的影响

用固态分子束外延技术生长了高应变In0.45Ga0.55As/GaAs量子阱材料. 研究了快速热退火对高应变InGaAs/GaAs量子阱材料光学性质的影响. 本文采用假设InGaAs/GaAs量子阱中的In-Ga原子扩散为误差函数扩散并解任意形状量子阱的薛定谔方程的方法，对不同退火温度下InGaAs/GaAs量子阱室温光致发光峰值波长拟合，得到了In原子在高应变InGaAs/GaAs量子阱中的扩散系数以及扩散激活能（0.88eV) .     

Influence of the cap layer thickness on photoluminescence properties in strained InGaAs/GaAs single quantum wells

The influence of the GaAs cap layer thickness on the luminescence properties in strained In_0.20Ga_0.80As/GaAs single quantum well (SQW) structures has been investigated using temperature-dependent photoluminescence (PL) spectroscopy. The luminescence peak is shifted to lower energy as the GaAs cap layer thickness decreases, which demonstrates the effect of the GaAs cap layer thickness on the strain of InGaAs/GaAs single quantum wells (SQW). We find the PL quenching mechanism is the thermal activation of electron hole pairs from the wells into the GaAs cap layer for the samples with thicker GaAs cap layer, while in sample with thinner GaAs cap layer exciton trapping on misfit dislocations is dominated.     

Strained-layer InGaAs-GaAs-InGaP buried-heterostructurequantum-well lasers on a low-composition InGaAs substrate byselective-area MOCVD

Aluminum-free buried-heterostructure quantum-well lasers have been successfully fabricated on low-composition InGaAs substrates. Selective-area metalorganic chemical vapor deposition (MOCVD) was utilized to investigate a variety of InGaAs quantum wells with a wide range of composition and thickness. Compressively strained quantum wells can be deposited thicker on substrates of InGaAs than GaAs before the generation of misfit dislocations. These deeper potential wells enable laser diodes with longer wavelengths (1.1504 μm) than GaAs-based emitters and higher characteristic temperatures (145 K) than InP-based devices     

Manifestation of <Emphasis Type="Italic">PT</Emphasis> symmetry in the exciton spectra of quantum wells

The reflection and photoluminescence excitation spectra under circular polarization of the incident light are measured in wide quantum wells whose width is much larger than the exciton Bohr radius. It is found that, in the absence of a magnetic field, the relation between the intensities of even and odd absorption peaks is reversed upon reversal of the sign of circular polarization.     

Chemical beam epitaxy and laser-modified chemical beam epitaxy of InGaAs using tris-dimethylaminoarsenic

The growth of In_xGaj_1−xAs (x = 0.13–0.25) on GaAs by chemical beam epitaxy (CBE) and laser-modified CBE using trimethylindium (TMIn), triethylgallium (TEGa), and tris-dimethylaminoarsenic (TDMAAs) has been studied. Reflection high-energy electron diffraction measurements were used to investigate the growth behavior of InGaAs at different conditions. X-ray rocking curve and lowtemperature photoluminescence (PL) measurements were used to characterize the InGaAs/GaAs pseudomorphic strained quantum well structures. Good InGaAs/GaAs interface and optical property were obtained by optimizing the growth condition. As determined by the x-ray simulation, laser irradiation during the InGaAs quantum well growth was found to enhance the InGaAs growth rate and reduce the indium composition in the substrate temperature range studied, 440–500°C, where good interfaces can be achieved. These changes, which are believed to be caused by laser-enhanced decomposition of TEGa and laser-enhanced desorption of TDMAAs, were found to depend on the laser power density as well. With laser irradiation, lateral variation of PL exciton peaks was observed, and the PL peaks became narrower.     

量子阱无序的窗口结构InGaAs/GaAs/AlGaAs量子阱激光器

对ＳｉＯ２薄膜在快速热退火条件下引起的空位诱导ＩｎＧａＡｓ／ＧａＡｓ应变量子阱无序和ＳｒＦ２薄膜抑制其量子阱无序的方法进行了实验研究。并将这两种技术的结合（称为选择区域量子阱无序技术）应用于脊形波导ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变量子阱激光器，研制出具有无吸收镜面的窗口结构脊形波导量子阱激光器。该结构３μｍ条宽激光器的最大输出功率为３４０ｍＷ，和没有窗口的同样结构的量子阱激光器相比，最大输出功率提高了３６％。在１００ｍＷ输出功率下，发射光谱中心波长为９７８ｎｍ，光谱半宽为１．２ｎｍ。平行和垂直方向远场发散角分别为７．２°和３０°     

InGaAs／InP应变量子阱的能带比较

利用K·P方法计算了InGaAs／InP的10.0nm阱党应变量子讲在1％压缩应变、无应变和1％伸张应变三种情况下的的能带结构及其态密度。结果表明在阱宽较宽时，伸张应变在开始很大能量之内子带较少，在一段能量范围之内，具有比无应变时小的态密度，因此从能带角度考虑，在伸张应变时，利用增大阱宽将可以改善器件性能。     

应变InGaAs/GaAs量子阱MOCVD生长优化及其在980 nm半导体激光器中的应用

使用低压MOCVD生长应变InGaAs/GaAs 980 nm量子阱.研究了生长温度、生长速度对量子阱光致发光谱(PL)的影响.并将优化后的量子阱生长条件应用于980 nm半导体激光器的研制中,获得了直流工作下,阈值电流为19 mA,未镀膜斜率效率为0.6 W/A,输出功率在100 mW的器件.     

InGaAs/AlGaAs量子阱中量子尺寸效应对PL谱的影响

本文采用金属有机物化学气相淀积(MOCVD)方法设计并生长了两组InGaAs／A1GaAs应变多量子阱，量子阱的厚度分别为3nm和6nm，对其光致发光谱(PL)进行了研究，二者的发光波长分别为843nm和942nm，用有限深单量子阱理论近似计算了由于量子尺寸效应和应变效应引起的InGaAs／A1GaAs量子阱带隙的改变，这解释了两组样品室温下PL发射波长变化的原因。     

980nm InGaAs应变量子阱激光器及组合件

利用分子束外延技术研制出了高质量InGsAs/GaAs应变量子阱材料及量子阱激光器.脊形波导窄条形量子阱激光器的阈值电流和微分量子效率分别为15mA和0.8 W/A,线性输出功率大于150mW,基横模输出功率可达100mW.InGaAs应变量子阱激光器和单模光纤进行了耦合,其组合件出纤光功率典型值为40mW,最大值可达60mW.显示出了高的基横模输出功率和高的耦合效率.其组合件在40～60mW下,中心发射波长在977nm.满足了对掺铒光纤高效率泵浦的波长要求,成功地研制出适于掺铒光纤放大器用的应变量子阱激光器.     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

Inhibited dark-line defect formation in strained InGaAs/AlGaAsquantum well lasers

Dark-line defect formation is compared in GaAs/AlGaAs and strained InGaAs/AlGaAs quantum well lasers. Dark-line defects have high growth velocity along 〈100〉 in GaAs quantum well lasers, causing rapid degradation. In contrast, the 〈100〉 dark-line defect is suppressed in the structures with a strained InGaAs quantum well, so that rapid degradation does not occur     

Exciton binding energy in semiconductor quantum dots

In the adiabatic approximation in the context of the modified effective mass approach, in which the reduced exciton effective mass μ = μ(a) is a function of the radius a of the semiconductor quantum dot, an expression for the exciton binding energy E _ex(a) in the quantum dot is derived. It is found that, in the CdSe and CdS quantum dots with the radii a comparable to the Bohr exciton radii a _ex, the exciton binding energy E _ex(a) is substantially (respectively, 7.4 and 4.5 times) higher than the exciton binding energy in the CdSe and CdS single crystals.     

On the gain properties of “thin” elastically strained InGaAs/InGaAlAs quantum wells emitting in the near-infrared spectral region near 1550 nm

The results of experimental studies of the gain properties of “thin” (3.2 nm thick) elastically strained InGaAs/InGaAlAs quantum wells emitting in the near-infrared spectral region near 1550 nm are presented. The results of studying the threshold and gain characteristics of stripe laser diodes with active regions based on “thin” quantum wells with a lattice–substrate mismatch of +1.0% show that the quantum wells under study exhibit a high modal gain of 11 cm^–1 and a low transparency current density of 46 A/cm² per quantum well.