Temperature Dependence Of Threshold Current Research Articles

Two-state lasing in a quantum dot racetrack microlaser.

The peculiarities of two-state lasing in a racetrack microlaser with an InAs/GaAs quantum dot active region are investigated by measuring the electroluminescence spectra at various injection currents and temperatures. Unlike edge-emitting and microdisk lasers, where two-state lasing involves the ground and first excited-state optical transitions of quantum dots, in racetrack microlasers, we observe lasing through the ground and second excited states. As a result, the spectral separation between lasing bands is doubled to more than 150 nm. A temperature dependence of threshold currents for lasing via ground and second excited states of quantum dots was also obtained.

Thermal Characterisation of Hybrid, Flip-Chip InP-Si DFB Lasers

WA detailed thermal analysis of a hybrid, flip-chip InP-Si DFB laser is presented in this work. The lasers were experimentally tested at different operating temperatures, which allowed for deriving their thermal performance characteristics: the temperature dependence of threshold current, lasing slope, and output spectrum. Using these data, the laser thermal resistance was calculated (Rth = 75.9 K/W), which allows for predicting the laser temperature during operation. This metric is also used to validate the thermal finite element models of the laser. A sensitivity study of the laser temperature was performed using these models, and multiple routes for minimising both the laser thermal resistance and thermal coupling to the carrier die are presented. The most effective way of decreasing the laser temperature is the direct attachment of a heat sink on the laser top surface.

Оптимизация температурной зависимости порогового тока гетеронанолазеров с учётом толщины и диэлектрических свойств материала волноводного нанослоя гетероструктур

Оптимизация температурной зависимости порогового тока гетеронанолазеров с учётом толщины и диэлектрических свойств материала волноводного нанослоя гетероструктур

Threshold current temperature dependence of quantum-dot photonic crystal surface-emitting lasers with respect to gain-cavity detuning.

We investigate threshold current temperature dependence of electrically injected quantum-dot (QD) photonic crystal (PC) surface-emitting lasers (SELs) with respect to wavelength detuning between QD gain peak and PC cavity resonance. The lasing emissions cover wavelengths from 1283 nm to 1318 nm. Almost infinite characteristic temperature is realized at certain temperature range for PCSEL with large negative gain-cavity detuning. Moreover, band-edge lasing mode is identified in our "PC slab-on-substrate" structure, and its far-field distribution is characterized as doughnut-shaped beam with azimuthal polarization.

Temperature-Dependent Threshold Current in InP Quantum-Dot Lasers

We explore the origins of the threshold current temperature dependence in InP quantum-dot (QD) lasers. While the internal optical mode loss does not change with temperature, the peak gain required to overcome the losses becomes more difficult to achieve at elevated temperature due to the thermal spreading of carriers among the available states. In 2-mm-long lasers with uncoated facets, this effect is responsible for 66% of the difference in threshold current density between 300 and 360 K. Spontaneous recombination current only makes up at most 10% of the total recombination current density over this temperature range, but the temperature dependence of the spontaneous recombination in the QD and quantum-well capping layers can be used, assuming only a simple proportional nonradiative recombination process, to explain the temperature dependence of the threshold current density.

Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling

We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 °C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-μm inner-aperture diameter and optimized for high-speed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.

Yellow AlGaInP/InGaP laser diodes achieved by pressure and temperature tuning

The emission wavelength of broad-area AlGaInP/InGaP quantum-well lasers is tuned by the application of high hydrostatic pressure and low temperature from 645 down to 575 nm, i.e., from the red through the orange to yellow spectral range. Emission powers up to 300 mW are obtained in the full tuning range. The pressure and temperature dependence of threshold currents indicates that leakage occurs into the L and X minima in the barriers.

Experimental study of temperature dependence of threshold characteristics in semiconductor VCSELs based on submonolayer InGaAs QDs

Temperature dependence of the threshold current for VCSELs based on submonolayer InGaAs QDs is studied experimentally. It is shown that detuning between the lasing wavelength and the gain spectrum peak must be used for a correct description of the temperature characteristics of laser diodes. An expression for describing the temperature dependence of the VCSEL threshold current is proposed, which takes into account not only the reduction of the maximum gain of the active region with rising temperature, but also the effect of the temperature dependence of detuning.

A comparative study of InAs quantum dot lasers with barriers of direct and indirect band gaps

We propose the idea of making quantum dot (QD) lasers by embedding direct-bandgap QDs in a short-period superlattice whose bandgap is indirect. In comparison with similar QD lasers with barriers of direct band gap, this technique not only reduces the temperature dependence of threshold current, but also leads to extremely small linewidth enhancement factor, making low-temperature sensitivity, low chirp, and narrow linewidth semiconductor lasers feasible.

650-nm lasers with narrow far-field divergence with integrated optical mode expansion layers

By means of numerical simulation of the optical and electrical performance, we have designed 650-nm GaInP-AlGaInP quantum-well lasers with mode expansion layers which have a narrow vertical far-field divergence without sacrificing threshold current or threshold current temperature dependence. We have reduced the measured vertical far-field divergence in a 650-nm laser structure from 35/spl deg/ to 24/spl deg/ full-width at half-maximum without changing the threshold current, operating voltage, or threshold current temperature dependence. We have also calculated the tolerances in the thickness and composition necessary to realize this design in practice.

Modelling the temperature dependence of threshold current, external differential efficiency and lasing wavelength in QW laser diodes

The temperature behaviour of GaAs/GaAlAs DQW-GRINSCH high-power laser diodes is calculated by means of a numerical model. The model includes a microscopic description of gain and spontaneous radiative recombination, a phenomenological description of interface and Auger recombination, and includes a pumping-current-dependent leakage. Based on the model, the temperature dependences of the macroscopic parameters of threshold current, external differential efficiency and wavelength are calculated. The resulting numerical values for these parameters are in excellent agreement with our experiments. Spontaneous radiative recombination is shown to be the dominant loss mechanism.

Threshold current temperature dependence of GaInP/(AlyGa1−y)InP 670 nm quantum well lasers

The temperature dependence of threshold current of (AlyGa1−y)InP/GaInP quantum well lasers (y=0.3, 0.4, and 0.5) has been investigated and used to characterize thermally activated loss mechanisms above room temperature. We show good agreement between activation energies measured by Arrhenius analysis and those expected for the loss of electrons from the well to the X-conduction band minima in the barrier. Our analysis uses measured band gaps of the actual structures, avoiding assumptions about the alloy compositions, spontaneous emission data to subtract radiative and other direct gap processes, and recent band gap data for this alloy system. This provides convincing experimental confirmation of the loss of electrons from the indirect minima as the preferred process causing the rise in current at high temperature in these lasers.

The temperature dependence of threshold current of chemical beam epitaxy grown InGaAs–InP lasers

The temperature dependence of threshold current between 130 and 310 K of 1.65 μm In0.53Ga0.47As–InP bulk lasers grown by chemical beam epitaxy has been measured. Comparison with a calculation of the spontaneous recombination current at threshold allows one to determine the proportion of current loss over this temperature range. It is found that the loss can be described using an Auger recombination component of the form Rauger=C′n3 exp(−Ea/kBT) where n is the carrier population density in the undoped active region. The activation energy Ea is found to be 39±5 meV which is in excellent agreement with the theoretical value for the conduction to heavy hole band/split-off to heavy hole band Auger process. The values obtained for the Auger coefficient C over the temperature range are in close agreement with published values obtained by time resolved photoluminescence.

Analysis of T0 in 1.3 μm multi-quantum-well and bulk active lasers

Temperature dependence of threshold in 1.3 μm semiconductor lasers is analyzed in terms of contributions due to gain, internal efficiency, internal loss, and nonradiative recombination. Rapid decrease of differential gain and roughly proportional increase in transparency carrier density are determined to dominate temperature dependence of threshold current. Auger recombination is found to play a secondary role in reducing T0 by compounding the effects of rapidly increasing threshold carrier density.

Temperature-dependent threshold and modulation characteristics in InGaAs/GaAs quantum-well ridge-waveguide lasers

The observed temperature dependence of threshold currents in InGaAs/GaAs quantum-well ridge-waveguide lasers is modeled. This method incorporates both experimental data and theoretical gain calculations. The results show that lateral leakage currents must be included in the ridge-waveguide laser models. Based on the same model, the temperature-dependent modulation characteristics for InGaAs/GaAs quantum-well ridge-waveguide lasers are also investigated.

Modeling and design of proton-implanted ultralow-threshold vertical-cavity laser diodes

Detailed theoretical models are presented and used for investigating the optical, electrical, and thermal characteristics of gain-guided vertical-cavity lasers. A two-dimensional description of current flow in the proton-implanted region is achieved. Heterojunctions are taken into account for the first time, and their influence on current spreading is demonstrated. Thorough finite-element calculations of the temperature profile in the whole device indicate the formation of a thermally induced waveguide. The temperature dependence of threshold current is evaluated, and it is shown that different mode positions greatly influence the output characteristics of the laser. The models are used to analyze the behavior of three-terminal vertical-cavity lasers. Good agreement is obtained between experimental and theoretical results. Using optimized design, record low threshold currents of 650 mu A have been achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of Auger recombination and differential gain on the temperature sensitivity of 1.5 μm quantum well lasers

The temperature sensitivity of both strained and lattice-matched 1.5 μm quantum well lasers has been studied. From a complete experimental investigation of the temperature behavior of carrier lifetime, gain, and internal loss, it is found that Auger recombination is not the dominant factor in affecting the temperature sensitivity of threshold currents in 1.5 μm lasers. Instead, the dominant contribution to the temperature dependence of threshold currents in 1.5 μm lasers is the change in differential gain with temperature—a characteristic not improved by strain.

Reduced temperature dependence of threshold current by broadband enhanced feedback: A new approach and demonstration

A new approach to reduce the rates of threshold current increase and external quantum efficiency decrease with increasing temperature in a semiconductor laser is proposed and demonstrated. This is based on the realization that the total laser cavity loss, which is normally relatively independent of wavelength, can be made to decrease with increasing wavelength. Since the gain peak of the laser shifts towards longer wavelength as temperature is increased, the rate of threshold current increase is thus reduced with increasing temperature. To implement this, we proposed and demonstrated the broadband enhanced feedback (BEF) approach using multilayer coatings, very weak or chirp gratings with peak reflectivity centered at the lasing wavelength corresponding to the maximum operating temperature desired. It was shown that the threshold-temperature coefficient T0 improved from the typical value of ∼45 K in long wavelength InGaAsP lasers (bulk active or MQW) to 85 K in BEF coated lasers. This scheme also simultaneously decreased the rate of quantum efficiency degradation with increasing temperature.

Temperature dependence of threshold of strained quantum well lasers

The temperature dependence of threshold current of strained quantum well lasers is analyzed both experimentally and theoretically. The measurements are performed on ridge waveguide In0.2Ga0.8As/GaAs multiquantum well lasers emitting near 1 μm. The carrier densities at threshold of these lasers are measured using very short current pulse injection. A simplified calculation of the radiative, nonradiative recombination rates and the relationship between gain and carrier density in strained quantum well lasers is described. The results of the calculation are compared with experimental results.

Waveguiding and temperature characteristics of threshold current and amplitude-phase coupling coefficient in double-heterostructure lasers

The problem of the electromagnetic wave propagation in a plane three-layer dielectric waveguide with complex values of the dielectric constant has been solved accurately. The solution of the problem, as applied to InGaAsP injection heterolasers makes it possible to explain the anomalously high temperature sensitivity of threshold current as the result of decreasing the waveguiding. It is evident that such imperfect features of the heterostructure, as the asymmetry or roughness of layers boundaries, worsen the temperature dependence of threshold current, and increase the coefficient of amplitude-phase coupling.