InAs/GaAs自组织量子点激发态的激射

将覆盖层引入生长停顿的量子点结构作为激光器有源区来研究量子点激光器受激发射机制．由于强烈的能带填充效应, 光致发光谱和电致发光谱中观察到对应于量子点激发态跃迁的谱峰,大激发时其强度超过基态跃迁对应的谱峰．最后激发态跃迁达到阈值条件, 激射能量比结构相似但不含量子点的激光器低,表明量子点激光器中首先实现受激发射是量子点的激发态．     

InGaAs量子点的自发发射及光增益

研究了InGaAs量子点材料自发发射、放大自发发射及光增益特性.实验发现InGaAs量子点材料随着注入电流密度的增加,其自发发射及放大自发发射光谱峰蓝移,表现出明显的能带填充现象.由于量子点材料尺寸及形状等存在一定的分布,在光谱中没有明显的对应量子点激发态的谱峰.由单程增益放大自发发射得到了量子点材料在不同注入电流密度下的光增益谱.结果表明存在由于量子点大小分布造成的量子点态非均匀展宽引起的增益峰蓝移和增益谱展宽现象.     

InGaAs量子点的自发发射及光增益

研究了InGaAs量子点材料自发发射、放大自发发射及光增益特性.实验发现InGaAs量子点材料随着注入电流密度的增加,其自发发射及放大自发发射光谱峰蓝移,表现出明显的能带填充现象.由于量子点材料尺寸及形状等存在一定的分布,在光谱中没有明显的对应量子点激发态的谱峰.由单程增益放大自发发射得到了量子点材料在不同注入电流密度下的光增益谱.结果表明存在由于量子点大小分布造成的量子点态非均匀展宽引起的增益峰蓝移和增益谱展宽现象.     

大尺寸InAs／GaAs量子点的静压光谱

在低温15K和0～9GPa范围内对厚度为7．3nm、横向尺寸为78nm的自组织InAs／GaAs量子点进行了压力光谱研究．观测到大量子点的基态与第一激发态发光峰，其压力系数只有69和72meV／GPa，比小量子点的压力系数更小．基于非线性弹性理论的分析表明失配应变与弹性系数随压力的变化是大量子点压力系数小的主要原因之一．压力实验结果还表明大量子点的第一激发态发光峰来源于电子的第一激发态到空穴的第一激发态的跃迁．     

量子点激光器研究进展综述

本文综述了量子点激光器的研究进展。介绍了量子点激光器的结构原理、生长及其优化；对量子点激光器光电特性从实验和建立模型进行描述；给出以速率方程描述的量子点激光器的动态特性如光增益均匀展宽、激射光谱控制、激发态迁移等；最后展望了量子点激光器的研究方向。     

光纤影响量子点激光器的运行状态数学模型研究

光纤影响下的量子点激光器运行状态具有非线性,构建基于势能函数分析和双态QDL激子模型的光纤影响量子点激光器的运行状态数学模型。在光纤注入状态下,分析量子点激光器的非线性动力学参数模型,结合非线性动力学态的分布和演化特性,利用时间序列、功率谱及相图分析的方法,在不同参数注入下进行量子点激光器的参数空间及运行状态动力学分布特性分析。以光学能级、光学限制因子以及光学增益因子等为约束参数,进行自由运行状态下的量子点激光器基态和激发态特性分析,实现光纤影响下量子点激光器的运行状态数学模型构建。实验结果表明,该模型能有效获取量子点激光器的最优微波线宽,在电流增加的过程中,自由运行光谱能级谱检测性能较好,研究结果为光纤网络互联和光存储提供理论基础。     

多孔硅上生长Ge量子点的光学特性

采用量子尺寸的多孔硅作为衬底,利用区域优先成核在多孔硅表面上成功地生长了Ge量子点.由于量子限制效应锗的PL谱发生了明显的蓝移,计算表明在傅里叶红外光谱中观察到的中红外(5-6μm)吸收峰是源于量子点中的亚能带跃迁(两个重空穴能级之间的跃迁),这为Ge量子点红外光探测器的应用提供了理论基础.     

多孔硅上生长Ge量子点的光学特性

采用量子尺寸的多孔硅作为衬底 ,利用区域优先成核在多孔硅表面上成功地生长了 Ge量子点 .由于量子限制效应锗的 PL 谱发生了明显的蓝移 ,计算表明在傅里叶红外光谱中观察到的中红外 (5— 6 μm)吸收峰是源于量子点中的亚能带跃迁 (两个重空穴能级之间的跃迁 ) ,这为 Ge量子点红外光探测器的应用提供了理论基础     

室温脉冲激射的纵向控制InAs量子点激光器

利用一种我们新近提出的ＭＢＥ自组织ＩｎＡｓ／ＧａＡｓ量子点生长方式,制成条型激光器,在室温脉冲工作条件下实现了激射．与测得的光致发光（ＰＬ）谱对照,发现激射峰位与量子点的ＰＬ谱峰位基本吻合．不同激光器结构的样品激射峰有相当大的移动,说明了激射来自量子点．在其它条件完全相同而仅有源区不同的条件下,纵向控制量子点激光器的阈值电流只是垂直耦合量子点激光器的１／３（６０ｍＡ∶２００ｍＡ）,我们给出了一个简单的解释,并据此提出了一种实现调节量子点激光器激射能量的方法．     

InGaAs/GaAs量子点类脊型激光器的激射特性

用MOCVD方法生长制备了多层InGaAs/GaAs量子点结构 ,并研制出量子点激光器。研究了多层量子点激光器阈值激射特性与量子点有源区结构之间的关系 ,结果表明激光器的阈值电流密度依赖于量子点的结构。通过采用多层量子点、对量子点层间进行耦合以及采用宽禁带AlGaAs作为量子点层势垒可以有效地降低激光器的阈值电流密度。获得了最低为 2 0A/cm2 的平均阈值电流密度。量子点激光器的激射波长也与有源区结构有关 ,随着量子点层数增加 ,激射峰向长波方向移动。     

Spectral Analysis of 1.55- $mu$m InAs–InP(113)B Quantum-Dot Lasers Based on a Multipopulation Rate Equations Model

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs–InP(113)B quantum dot (QD) lasers emitting at 1.55 $mu$m. The numerical model is based on a multipopulation rate equations analysis. Calculations take into account the QD size dispersion as well as the temperature dependence through both the inhomogeneous and the homogeneous broadenings. This paper demonstrates that the model is capable of reproducing the spectral behavior of InAs–InP QD lasers. Especially, this study aims to highlight the transition of the lasing wavelength from the ground state (GS) to the excited state (ES). In order to understand how the QD laser turns on, calculated optical spectra are determined for different cavity lengths and compared to experimental ones. Unlike InAs–GaAs QD lasers emitting at 1.3 $mu$m, it is shown that a continuous transition from the GS to the ES is exhibited because of the large inhomogeneous broadening comparable to the GS and ES lasing energy difference.      

Influence of inhomogeneous broadening and deliberately introduced disorder on the width of the lasing spectrum of a quantum dot laser

Analytical expressions for the shape and width of the lasing spectra of a quantum-dot (QD) laser in the case of a small (in comparison with the spectrum width) homogeneous broadening of the QD energy levels have been obtained. It is shown that the dependence of the lasing spectrum width on the output power at room temperature is determined by two dimensionless parameters: the width of QD distribution over the optical-transition energy, normalized to temperature, and the ratio of the optical loss to the maximum gain. The optimal dimensions of the laser active region have been found to obtain a specified width of the emission spectrum at a minimum pump current. The possibility of using multilayer structures with QDs to increase the lasing spectrum’s width has been analyzed. It is shown that the use of several arrays of QDs with deliberately variable optical-transition energies leads to broadening of the lasing spectra; some numerical estimates are presented.     

Electroluminescence of injection lasers based on vertically coupled quantum dots near the lasing threshold

Electroluminescence spectroscopy has been used in a wide range of temperatures (77–300 K) and driving current densities to study a laser heterostructure based on vertically coupled self-assembled InGaAs quantum dots (QD). It has been found that lasing occurs via the QD ground state in the entire temperature range. The temperature-independent position of the emission peak corresponding to the second excited state in QDs is explained.     

Longitudinal spatial hole burning in a quantum-dot laser

Detailed theoretical analysis of longitudinal spatial hole burning in quantum-dot (QD) lasers is given. Unlike conventional semiconductor lasers, escape of thermally excited carriers from QDs, rather than diffusion, is shown to control the smoothing-out of the spatially nonuniform population inversion and multimode generation in QD lasers. The multimode generation threshold is calculated as a function of structure parameters (surface density of QDs, QD size dispersion, and cavity length) and temperature. A decrease in the QD size dispersion is shown to increase considerably the relative multimode generation threshold. The maximum tolerable QD size dispersion and the minimum tolerable cavity length, at which lasing is possible to attain, are shown to exist. Concurrent with the increase of threshold current, an increase of the multimode generation threshold is shown to occur with a rise in temperature. Ways to optimize the QD laser, aimed at maximizing the multimode generation threshold, are outlined     

Threshold temperature dependence of lateral-cavity quantum-dotlasers

The threshold temperature dependence for quantum-dot (QD) lasers with different degrees of inhomogeneous broadening are compared. By reducing the inhomogeneous linewidth, the “negative” temperature dependence due to thermal coupling of the QD ensemble can be nearly eliminated, Stable ground state lasing is obtained with a single-layer QD density of -5×10¹⁰ cm^-2 for a long cavity laser, while lower gain QDs and shorter cavity lengths lase on well-resolved higher energy levels     

Rate equation model for nonequilibrium operating conditions in aself-organized quantum-dot laser

A nonequilibrium rate equation model is presented and analyzed for the self-organized quantum dot (QD) laser. The model assumes the QD zero dimensional levels are coupled to a thermal electron distribution in the wetting layer through reservoir rate equations. By including the energy dependence of the wetting layer reservoir versus temperature, the model accounts for the spectral narrowing of the gain with increasing temperature, the negative temperature coefficient of the lasing threshold, and a reduction of the spectral hole burning with increasing temperature, all found experimentally in QD lasers     

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

Modeling and simulation of InAs/GaAs quantum dot lasers

Based on the analysis of carrier dynamics in quantum dots (QDs), the numerical model of InAs/GaAs QD laser is developed by means of complete rate equations. The model includes four energy levels and among them three energy levels join in lasing. A simulation is conducted by MATLAB according to the rate equation model we obtain. The simulation results of PI characteristic, gain characteristic and intensity modulation response are reasonable. Also, the relations between the left facet reflectivity of laser cavity and threshold current as well as modulation bandwidth are studied. It is indicated that the left facet reflectivity increasing can result in reduced threshold current and improved modulation bandwidth, which is in accordance with experimental results. The internal mechanism of QD lasers is fully described with the rate equation model, which is helpful for QD lasers research.     

Very low threshold current density room temperature continuous-wavelasing from a single-layer InAs quantum-dot laser

Continuous-wave (CW) lasing operation with a very low threshold current density (J_th=32.5 A/cm²) has been achieved at room temperature by a ridge waveguide quantum-dot (QD) laser containing a single InAs QD layer embedded within a strained InGaAs quantum well (dot-in-well, or DWELL structure). Lasing proceeds via the QD ground state with an emission wavelength of 1.25 μm when the cavity length is longer than 4.2 mm. For a 5-mm long QD laser, CW lasing has been achieved at temperatures as high as 40°C, with a characteristic temperature T₀ of 41 K near room temperature. Lasers with a 20 μm stripe width have a differential slope efficiency of 32% and peak output power of >10 mW per facet (uncoated)