Temperature dependence of the lasing characteristics of the 1.3 µm InGaAsP-InP and GaAs-Al0.36Ga0.64As DH lasers

We report here our experimental observations on the temperature dependence of threshold current, carrier lifetime at threshold, external differential quantum efficiency, and gain of both the 1.3 μm InGaAsP-InP and GaAs-AlGaAs double heterostructure (DH) lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 μm InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 μm InGaAsP DH laser. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115-350 K. The experimental results are discussed with reference to the various mechanisms that have been proposed to explain the observed temperature dependence of threshold of InGaAsP DH lasers. We find that inclusion of a calculated nonradiative Auger recombination rate can explain the observed temperature dependence of threshold current, carder lifetime at threshold, gain, and also the sublinearity of the spontaneous emission with injection current of the 1.3 μm InGaAsP-InP DH laser. Measurement of the nonradiative component of the carrier lifetime (τA) as a function of injected carrier density (n) shows thattau_{A}^{-1} sim n^{2.1}which is characteristic of an Auger process.     

InAs/InGaAs/GaAs quantum dot lasers of 1.3 μm range with high(88%) differential efficiency

Multiple layers (up to 10) of InAs/InGaAs/GaAs quantum dots considerably enhance the optical gain of quantum dot lasers emitting around 1.3 μm. A differential efficiency as high as 88% has been achieved in these lasers. An emission wavelength of 1.28 μm, threshold current density of 147 A/cm², differential efficiency of 80%, and characteristic temperature of 150 K have been realised simultaneously in one device     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

Effect of temperature on the stimulated emission from GaAs p-n junctions

The temperature dependence of the threshold current density was examined for a series of GaAs injection lasers with different lengths but otherwise identical structure. From a plot of threshold current density as a function of reciprocal length at constant temperature, the gain and loss factor can be calculated. The laser losses exhibit only a small temperature dependence in the range from 4·2 to 300°K. The reciprocal gain factor, however, has the same temperature dependence as the threshold current density j_t. The detailed nature of the temperature dependence of j_t does depend on the length of the laser and on the doping level in the active region. The influence of these two parameters is discussed and compared with theoretical predictions.     

Theoretical study of the temperature dependence of 1.3-μmAlGaInAs-InP multiple-quantum-well lasers

The temperature dependence of the differential gain, carrier density, and transparency current density for 1.3-μm AlGaInAs-InP multiple-quantum-well lasers has been theoretically studied using the optical gain calculation from 250-380 K. The characteristic temperatures of the carrier density and differential gain at threshold are calculated to be 254 and 206 K, respectively. The Auger current density accounts for more than 50% of the total current density. The leakage current density exhibits the highest temperature sensitivity and becomes an essential part of the total current density at a high temperature. The calculated characteristic temperatures of the transparency and threshold current densities are 106 and 84 K, respectively, which agree well with the reported experimental results     

High-speed modulation of long-wavelength In1-xGaxAsyP1-y andIn1-x-yGaxAlyAs strained quantum-welllasers

In_1-xGa_xAs_1-yP_y quantum-well (QW) lasers with compressive strain and In_1-x-yGa_xAl_yAs QW lasers with two strain types (compressively strained and lattice matched) for 1.55-μm telecommunication applications are investigated both in the steady-state and high-speed microwave modulation schemes. Under steady-state electric bias, the gain and intrinsic loss are measured based on the well-known Hakki-Paoli method from below threshold to threshold. The photon lifetime is obtained from this measurement. A comprehensive theoretical gain model with realistic band structure, including valence band mixing and many-body effects, is then used to fit the experimentally obtained modal gain profiles and extract the carrier density and, therefore, the differential gain. In the high-speed microwave modulation scheme, the experimental modulation response curves are fitted by the theory and parameters such as the differential gain and K factor are obtained. The differential gain agrees very well with the value obtained from the steady-state direct optical gain measurement. The comparison of two material systems will be important to design high-bandwidth high-performance semiconductor lasers in order to meet requirements of 1.55-μm telecommunication applications     

Microscopic simulation of the temperature dependence of static and dynamic 1.3-/spl mu/m multi-quantum-well laser performance

The temperature dependence of the performance of 1.3-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers is analyzed using detailed microscopic simulations. Both static and dynamic properties are extracted and compared to measurements. Devices with different profiles of acceptor doping in the active region are studied. The simulation takes into account microscopic carrier transport, quantum mechanical calculation of the optical and electronic quantum well properties, and the solution of the optical mode. The temperature dependence of the Auger coefficients is found to be important and is represented by an activated form. Excellent agreement between measurement and simulation is achieved as a function of both temperature and doping profile for static and dynamic properties of the lasers, threshold current density, and effective differential gain. The simulations show that the static carrier density, and hence the contribution to the optical gain, varies significantly from the quantum wells on the p-side of the active layer to those on the n-side. Furthermore, the modal differential gain and the carrier density modulation also vary. Both effects are a consequence of the carrier dynamics involved in transport through the MQW active layer. Despite the complexity of the dynamic response of the MQW laser, the resonance frequency is determined by an effective differential gain, which we show can be estimated by a gain-weighted average of the local differential gain in each well.     

Effects of Lateral Diffusion on the Temperature Sensitivity of the Threshold Current for 1.3-$mu{hbox {m}}$ Double Quantum-Well GaInNAs–GaAs Lasers

We present an experimental and theoretical investigation of the temperature dependence of the threshold current for double quantum well GaInNAs-GaAs lasers in the temperature range 10 degC-110 degC. Pulsed measurements of the threshold current have been performed on broad and narrow ridge wave guide (RWG) lasers. The narrow RWG lasers exhibit high characteristic temperatures (T₀) of 200 K up to a critical temperature (T_c), above which T₀ is reduced by approximately a factor of 2. The T0-values for broad RWG lasers are significantly lower than those for the narrow RWG lasers, with characteristic temperatures on the order of 100 (60) K below (above) T_c. Numerical simulations, using a model that accounts for lateral diffusion effects, show good agreement with experimental data and reveal that a weakly temperature dependent lateral diffusion current dominates the threshold current for narrow RWG lasers.     

GaInP-(AlyGa1-y)InP 670 nm quantum-welllasers for high-temperature operation

We have examined the operation of 670 nm (Al_yGa_1-y )InP/GaInP quantum well lasers with different aluminium compositions (y=0.3, 0.4, and 0.5) in the barrier/waveguide layer so as to vary the optical confinement factor and hence the threshold gain requirement. Lasers with y=0.3 have the lowest threshold current over the range 200-400 K despite having the narrowest barrier band gap of the three structures. The measured intensity of spontaneous emission due to transitions in the well increases linearly with temperature between 280-400 K, whilst that from the barrier increases exponentially. An Arrhenius treatment of the emission from the barrier gives an activation energy of 198 meV±25 meV which is in excellent agreement with the value predicted from the energy band diagram. When the experimental temperature dependence of the well and barrier contributions are removed from the measured threshold current, the remaining excess current has an activation energy of around 320 meV which is in excellent agreement with the value for thermally activated loss of electrons via the X conduction band minima. Since the X gap is insensitive to composition there is no increase in this leakage current when y is reduced so the overall effect is for the current to go down due to the reduced gain requirement per well     

Three-dimensional arrays of self-ordered quantum dots for laser applications

Semiconductor heterostructures with quantum dots (QDs) are experimentally proved to exhibit properties expected for zero-dimensional systems, e.g. ultrasharp luminescence lines up to high temperatures, massively increased exciton oscillator strength per unit volume and temperature insensitivity of the radiative lifetime. When applied to the injection lasers these advantages help to increase strongly material gain, differential gain, to improve temperature stability of the threshold current and to suppress chirp. Threshold current densities as low as 60 A/cm² at 300 K are obtained. Formation of QDs with properties satisfying device requirements on QD size, shape, uniformity and density became possible by utilizing self-ordering phenomena on crystal surfaces.     

DC and Dynamic Characteristics of P-Doped and Tunnel Injection 1.65-μm InAs Quantum-Dash Lasers Grown on InP (001)

We have studied the characteristics of 1.65-mum InAs self-organized quantum-dash lasers grown on InP (001) substrates, wherein special techniques of p-doping of quantum dashes and tunnel injection are incorporated for the first time. We measured a very large T₀ (196 K) in p-doped quantum-dash lasers, accompanied by an increase in threshold current density (J_th~1600 A/cm² ), compared to the undoped quantum-dash lasers (T₀=76 K and J_th~950 A/cm²). The p-doped lasers exhibit a maximum 3-dB bandwidth of 8 GHz, chirp ~1.0 Aring, and alpha-parameter ~1.0 (measured at subthreshold bias conditions) at a temperature of 278 K. Similar undoped quantum-dash lasers exhibit a 3-dB bandwidth of 6 GHz. A self-consistent model, that includes Auger recombination in quantum dashes, is developed to calculate the threshold current at various temperatures. A comparison of the calculated threshold current and T₀ with measured values reveals that Auger recombination in quantum dashes plays a major role in determining the values of threshold current and T₀ in both undoped and p-doped quantum-dash lasers. While p-doping increases the gain and differential gain, the presence of wetting layer states, the relatively large inhomogeneous broadening of quantum dashes, and the substantially increased Auger recombination upon p-doping severely limit the potential benefits. Superior characteristics, including large modulation bandwidth (f_{-3 dB}~12 GHz), near-zero alpha-parameter, and very low chirp (~0.3 Aring), are achieved when the technique of tunnel injection is also utilized     

Operating characteristics of single-quantum-well AlGaAs/GaAshigh-power lasers

The operating characteristics of six types of graded-index separate confinement heterostructure single-quantum-well wide-stripe lasers grown by metalorganic chemical vapor deposition are reported. The lasers exhibited intrinsic mode losses as low as 3 cm^-1 and internal quantum efficiencies near unity. Measured differential gain coefficients range from 3.7 to 6.5 cm/A, and extrapolated transparency current densities range from 54 to 145 A/cm². These wide-stripe lasers are typically multilongitudinal mode and exhibit narrowing of the gain envelope and lateral far-field pattern as the cavity length increases. The high value of T₀(>200 K) at long cavity lengths in conjunction with the low current density permits junction-side-up operation to CW optical powers of 0.5-0.7 W/facet, at which level catastrophic facet damage occurs on the uncoated devices. A maximum power conversion efficiency of 57% was measured on the laser structure exhibiting the lowest threshold current     

Temperature analysis and characteristics of highly strainedInGaAs-GaAsP-GaAs (λ > 1.17 μm) quantum-well lasers

Characteristic temperature coefficients of the threshold current (T₀) and the external differential quantum efficiency (T₁) are studied as simple functions of the temperature dependence of the physical parameters of the semiconductor lasers. Simple expressions of characteristic temperature coefficients of the threshold current (T₀) and the external differential quantum efficiency (T₁) are expressed as functions as physical parameters and their temperature dependencies. The parameters studied here include the threshold (J_th) and transparency (J_tr ) current density, the carrier injection efficiency (η_inj ) and external (η_d) differential quantum efficiency, the internal loss (α_i), and the material gain parameter (g_o). The temperature analysis is performed on low-threshold current density (λ = 1.17-1.19 μm) InGaAs-GaAsP-GaAs quantum-well lasers, although it is applicable to lasers with other active-layer materials. Analytical expressions for T ₀ and T₁ are shown to accurately predict the cavity length dependence of these parameters for the InGaAs active lasers     

高功率980nm垂直腔面发射激光器的温度特性

应变补偿量子阱结构因带宽大、增益高和波长漂移速度低等特点而成为近年来研究的热点.首次介绍了国内980 nm 高功率InGaAs/GaAsP应变补偿量子阱结构的垂直腔面发射激光器(VCSEL) 变温实验,测得脉冲条件下600 μm直径的器件在10-100℃温度范围内发射波长漂移速度为0.05 nm/K,阈值电流随温度变化呈现先缓慢下降后迅速上升的特性.结合VCSEL反射谱、PL谱和增益峰值波长漂移速度,对器件阈值电流特性进行了合理的分析和解释.连续工作状态下,测试得到器件峰值功率为1 W,根据波长与耗散功率的实验曲线及热阻计算公式,可估算出垂直腔面发射激光器热阻值为10 K/W.     

In(Ga)As/GaAs self-organized quantum dot lasers: DC andsmall-signal modulation properties

Self-organized growth of InGaAs/GaAs strained epitaxial layers gives rise to an ordered array of islands via the Stranski-Krastanow growth mode, for misfits >1.8%. These islands are pyramidal in shape with a base diagonal of ~20 nm and height of ~6-7 nm, depending of growth parameters. They therefore exhibit electronic properties of zero-dimensional systems, or quantum dots. One or more layers of such quantum dots can be stacked and vertically coupled to form the gain region of lasers. We have investigated the properties of such single-layer quantum dot (SLQD) and multilayer quantum dot (MLQD) lasers with a variety of measurements, including some at cryogenic temperatures. The experiments have been complemented with theoretical calculations of the electronic properties and carrier scattering phenomena in the dots. Our objective has been to elucidate the intrinsic behavior of these devices. The lasers exhibit temperature independent threshold currents up to 85 K, with T₀⩽670 K. Typical threshold currents of 200-μm long room temperature lasers vary from 6 to 20 mA. The small-signal modulation bandwidths of ridge waveguide lasers are 5-7.5 GHz at 300 K and increased to >20 GHz at 80 K. These bandwidths agree well with electron capture times of ~30 ps determined from high-frequency laser impedance measurements at 300 K and relaxation times of ~8 ps measured at 18 K by differential transmission pump-probe experiments. From the calculated results we believe that electron-hole scattering intrinsically limits the high-speed performance of these devices, in spite of differential gains as high as ~7×10^-14 cm² at room temperature     

Dynamics and Temperature-Dependence of 1.3-μm GaInNAs Double Quantum-Well Lasers

We have measured the small-signal modulation response of 1.3-mum ridge waveguide GaInNAs double quantum-well lasers over a wide range of temperatures (25 degC-110 degC) and analyzed the temperature dependence of the modulation bandwidth and the various bandwidth limiting effects. The lasers have low threshold currents and high differential efficiencies with small temperature dependencies. A short-cavity (350 mum) laser has a modulation bandwidth as high as 17 GHz at room temperature, reducing to 4 GHz at 110 degC, while a laser with a longer cavity (580 mum) maintains a bandwidth of 8.6 GHz at 110 degC. We find that at all ambient temperatures the maximum bandwidth is limited by thermal effects as the temperature increases with current due to self-heating. The reduction and subsequent saturation of the resonance frequency with increasing current is due to a reduction of the differential gain and an increase of the threshold current with increasing temperature. We find large values for the differential gain and the gain compression factor. The differential gain decreases linearly with temperature while there is only a weak temperature dependence of the gain compression. At the highest temperature we also find evidence for transport effects that increase the damping rate and reduce the intrinsic bandwidth     

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current Ithcalculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.     

Room-temperature continuous-wave quantum cascade lasers grown by MOCVD without lateral regrowth

We report on room-temperature continuous-wave (CW) operation of /spl lambda//spl sim/8.2 /spl mu/m quantum cascade lasers grown by metal-organic chemical vapor deposition without lateral regrowth. The lasers have been processed as double-channel ridge waveguides with thick electroplated gold. CW output power of 5.3 mW is measured at 300 K with a threshold current density of 2.63 kA/cm/sup 2/. The measured gain at room temperature is close to the theoretical design, which enables the lasers to overcome the relatively high waveguide loss.     

Gain measurements in 1.3 µm InGaAsP-InP double heterostructure lasers

The net gain per unit length (G) versus current (I) is measured at various temperatures for 1.3 μm InGaAsP-InP double heterostructure lasers.Gis found to vary linearly with the currentIat a given temperature. The gain bandwidth is found to decrease with decreasing temperature. The lasing photon energy decreases at 0.325 meV/K with increasing temperature. Also, the slopedG/dIat the lasing photon energies decreases with increasing temperature. This decrease is more rapid forT > sim210K. This faster decrease is consistent with the observed higher temperature dependence of threshold (low T0at high temperatures) of 1.3 μm InGaAsP lasers. A carrier loss mechanism, due to Auger recombination, also predicts thatdG/dIshould decrease much faster with increasing temperature at high temperatures. We also find that the slopedG/dIdecreases slowly with increasing temperature for a GaAs laser, which is consistent with the observed temperature dependence of threshold of these lasers.     

InGaN量子阱激光器增益和阈值电流的理论计算

根据现有的材料参数，计算了Ｉｎ０．２Ｇａ０．８Ｎ／Ｉｎ０．０５Ｇａ０．９５Ｎ量子阱激光器的增益、阈值电流密度以及阈值与温度的关系。理论分析表明氮化物蓝绿光激光器的阈值电流密度是ＧａＡｓ材料的５倍以上，但其特征温度可接近５００Ｋ。