InGaAs quantum dot lasers with submilliamp thresholds and ultra-lowthreshold current density below room temperature

Continuous-wave operation of InGaAs quantum dot lasers is studied. A very low threshold current of 460 μA is achieved at 200 K for a 5 μm×1170 μm oxide-confined stripe laser. For a larger stripe width of 11 μm, a threshold current density of 5.2A/cm² is demonstrated. The characteristic threshold temperature is -700 K in the temperature range of 14-200 K, and drops rapidly around room temperature     

Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers

It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.     

Room temperature, continuous-wave lasing near 1300 nm in microdisks with quantum dot active regions

Room temperature, optically-pumped, continuous-wave lasing near 1300 nm in microdisk resonant cavities with InAs quantum dot active regions is reported for the first time. Lasing occurred in devices with diameters between 6 and 7 /spl mu/m with incident threshold pumping powers as low as 2 mW     

Features of simultaneous ground- and excited-state lasing in quantum dot lasers

The lasing spectra and light-current (L-I) characteristics of an InAs/InGaAs quantum dot laser emitting in the simultaneous lasing mode at the ground- and excited-state optical transitions are studied. Lasing and spontaneous emission spectra are compared. It is shown that ground-state quenching of lasing is observed even in the absence of active region self-heating or an increase in homogeneous broadening with growth in the current density. It is found that the intensities of both lasing and spontaneous emission at the ground-state transition begin to decrease at a pump intensity that significantly exceeds the two-level lasing threshold. It is also found that different groups of quantum dots are involved in ground- and excited-state lasing.     

Low threshold,room temperature pulsed and quasi-continuous lasing in optically pumped CdZnTe/ZnTe quantum wells

We report room temperature optically pumped lasing with a threshold of 6 kW/ cm² in a CdZnTe/ZnTe multiple quantum well. Quasi-continuous optically pumped lasing at room temperature has also been achieved. We discuss the influence of composition on mode confinement and show that the lowest thresholds are expected in samples in which the active layer is slightly zinc-rich compared to the cladding layers.     

Temperature dependent lasing characteristics of InAs/InP(100) quantum dot laser

We report on the lasing characteristics of InAs/InP(100) quantum dots laser through changing the temperature under continuous-wave mode. Three lasing peaks are simultaneously observed at temperature of 80 K and the lasing order of each peak is unrelated with each other when injection current increases. Laser spectra obtained under fixed current for different temperatures show a drastic influence on their shape. A large spectral broadening is observed at low temperature, while the width of lasing spectra gradually narrows when the operating temperature increased. The lasing process of quantum dot laser is obviously different from that of a reference quantum well laser in the same wavelength region. In addition, very high wavelength stability of 0.088 nm/K in the temperature range of 80–300 K is obtained, which is 6.2 times better than that of reference quantum well laser.     

Annealing behavior of InAs/GaAs quantum dot structures

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.     

1516nm room temperature CW operation of quantum dot InAs/InP(311)B singlemode laser

Reported is the first demonstration of the performance and properties of a singlemode Fabry-Perot laser processed from InAs/InP(311)B quantum dot material, which gives emission at 1.516 mum under continuous-wave operation at room temperature     

Optical and morphological properties of InGaAs/AIGaAs self-assembled quantum dot nanostructures for 980 nm room temperature emission

This work deals with the study of optical and morphological properties of InGaAs/AlGaAs quantum dot （QD） structures grown by molecular beam epitaxy （MBE）. Photoluminescence （PL） emission energies, activation energies of PL quenching and QD sizes are studied as functions of the Al content in the AlyGal-yAs confining layers （CL）. We show that the PL emission energy of In（Ga）As/AlyGal-yAs QD structures increases with increasing y and that the sizes of InAs/AlyGal-yAs QDs decrease with increasing y. By the comparison of the experimental results with those of an effective-mass model developed to calculate the QD fundamental transition energies, we show that the blueshift of emission energy has to be ascribed not only to the increase in barrier discontinuities that confine the carriers into QDs but even to effects related to changes of the QD morphology dependent on CL composition. Moreover, we show that the Al content in the barriers determines also the activation energy of thermal quenching of PL, which depends on the thermal escape of carriers from QD levels. These studies resulted in the preparation of structures with efficient light-emission in the 980 nm spectral window of interest for lightwave communications.     

Exciton characteristics and exciton luminescence of silicon quantum dot structures

The exciton binding energy, the energies of the basic radiative exciton transition, and the zerophonon radiative lifetime of excitons in silicon quantum dots embedded in the SiO_x matrix are calculated in effective mass approximation with quadratic dispersion relation. In addition, the spectra of steady-state photoluminescence and of time-resolved photoluminescence of excitons in the silicon quantum dots are calculated, and the kinetics of the photoluminescence relaxation is considered. The theory is compared with the experiment. It is shown that, for nanostructures involving silicon quantum dots with diameters smaller than 4 nm, the governing factor in the broadening of the spectral photoluminescence bands is the effect of mesoscopic quantum fluctuations. In this case, either an even one dangling bond at the interface, or one intrinsic point defect, or one foreign atom located inside the small-sized nanocrystallite or in its close surroundings produces a pronounced effect on the energy of the exciton transition.     

Continuous-wave lasing of single-mode metamorphic quantum dot lasers for the 1.5-μm spectral region

Lasers based on InAs/InGaAs quantum dots grown on metamorphic (In,Ga,Al)As layers deposited by MBE on GaAs substrates exhibited emission near 1.5 μm with a differential quantum efficiency of about 50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm^?2 without significant degradation. A maximum continuous-wave output power of 220 mW is obtained. Neither current nor beam filamentation was observed up to the highest pumping levels.     

Charge accumulation of quantum dots at room temperature

The accumulation of charge in InGaAs quantum dots has been measured at room temperature by the photoelectrochemical capacitance-voltage (CV) technique for the first time. A carrier per quantum dot ratio greater than four has been observed. The use of atomic force microscopy and low temperature and room temperature photoluminescence (PL) confirm the existence of quantum dots. Also, a possible excited state is indicated by room temperature PL in a sample with small quantum dots.     

Absorption in laser structures with coupled and uncoupled quantum dots in an electric field at room temperature

The absorption of uncoupled and tunnel-coupled vertically correlated quantum dots (QDs), measured at room temperature, has been experimentally compared. It is revealed that matching of the laser wavelength and Stark shift for laser structures with tunnel-coupled QDs leads to resonant absorption with formation of bound and antibound exciton states with a splitting energy of ～62 meV between them in QD molecules. For these states, an external field causes a large linear Stark shift (up to 68 meV). For uncoupled QDs, one resonant absorption peak with the formation of an exciton (for which the Stark shift does not exceed 13 meV) is observed.     

Effect of nonradiative recombination centers on photoluminescence efficiency in quantum dot structures

The influence of dislocations on photoluminescence (PL) intensity in structures with InAs-GaAs quantum dots (QD) has been studied. The structural characteristics of samples were studied by transmission electron microscopy in bright-field and weak-beam dark-field diffraction conditions. At temperatures below room temperature and for moderate excitation density, the PL intensity in a structure containing large clusters with dislocations was about the same as in a structure with a significantly lower density of clusters. In contrast, the measurement of PL intensity at elevated temperatures and high excitation densities allows an accurate estimation of the structural perfection of QD structures. The overgrowth of QDs with a thin (1–2 nm) GaAs layer with subsequent annealing reduces the density of clusters with dislocations and significantly improves the temperature stability of the PL intensity.     

Electro-magnetic weak coupling optical polaron and temperature effect in quantum dot

We investigate the influence of the electric field and magnetic fields on the ground state energy of a polaron in a spherical semiconductor quantum dot (QD) using the modified Lee Low Pines (LLP) method.The numerical results show the increase of the ground state energy with the increase of the electric field and the electron-phonon coupling constant, and the decrease with the magnetic field and the longitudinal confinement length.It is also seen that the temperature is an increasing function of the cyclotron frequency and the coupling constant whereas it decreases with the electric field strength.The modulation of the electric field, the magnetic field and the confinement length leads to the control of decoherence in the system.     

Lasing at 1.5 µm in quantum dot structures on GaAs substrates

Lasing at 1488–1515 nm in the temperature range 20–83°C was obtained in structures with an active region based on multiply stacked arrays of self-organized quantum dots grown on GaAs substrates. The threshold current density of a laser with four cleaved facets was 800 A/cm2 at room temperature. The method of wavelength extension is based on the use of a metamorphic buffer layer with an In content of about 20% intended for relieving the lattice mismatch stress.     

InAs quantum dot photonic crystal lasers and their temperature dependence

We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination.     

Determination of the density of states in quantum wells and quantum dot arrays by the capacitance-voltage method

The possibility of determining the electronic density of states in quantum wells and quantum dot arrays in heterostructures from the capacitance-voltage curve is investigated. In heterostructures fluctuations of the composition and geometrical dimensions play an important role. It is shown that to reconstruct the exact density of states from the measured capacitance-voltage curve is impossible, because this problem is ill-posed from the mathematical point of view. An approximate method is proposed for solving the problem, involving the determination of a “reduced” density of states. It is shown that the reduced density of states is close to the true density if the characteristic energy scale governing the variation of the latter is much greater than the thermal energy kT. The proposed method is used to find the density of states in the conduction band of a quantum well in an In_0.22Ga_0.78As/GaAs heterostructure. Fiz. Tekh. Poluprovodn. 33, 1246–1252 (October 1999)     

晶格畸变分析及其在半导体量子点结构中的应用

在适当的成像条件下可以直接从高分辨透射电子像（HRTEM）以接近原子级的分辨率进行晶格畸变分析。本综述介绍晶格畸变分析（LADIA）程序包及其在半导体自组装量子点（QD）系统中的应用。对多层InP小QD系统中畸变分布的分析表明：光致发光（PL）能量峰位的红移和QD中的应变弛豫直接相关。在慢速生长的InAs大QD系统中应变引起的元素互溶是PL峰位蓝移的主要因素。多层系统中QD的垂直叠合可解释为间隔层厚度低于临界值时生长前沿的横向张应变的作用。研究了生长以后不同条件快速退火对QD稳定性的影响,观测到垂直叠合的InPQD中出现各向异性的退火不稳定性。