The effect of temperature dependent processes on the performance of1.5-μm compressively strained InGaAs(P) MQW semiconductor diodelasers

We describe measurements of the threshold current I_th and spontaneous emission characteristics of InGaAs (P)-based 1.5-μm compressively strained multiple-quantum-well semiconductor lasers from 90 K to above room temperature. We show that below a break-point temperature, T_B≈130 K, I_th and its temperature dependence are governed by the radiative current. Above this temperature, a thermally activated Auger recombination process becomes the dominant recombination mechanism responsible for both I_th and its temperature sensitivity. At room temperature nonradiative Auger recombination is found to account for approximately 80% of the threshold current in these devices     

Temperature dependence of the threshold current density of aquantum dot laser

Detailed theoretical analysis of the temperature dependence of threshold current density of a semiconductor quantum dot (QD) laser is given. Temperature dependences of the threshold current density components associated with the radiative recombination in QDs and in the optical confinement layer (OCL) are calculated. Violation of the charge neutrality in QDs is shown to give rise to the slight temperature dependence of the current density component associated with the recombination in QD's. The temperature is calculated (as a function of the parameters of the structure) at which the components of threshold current density become equal to each other. Temperature dependences of the optimum surface density of QD's and the optimum thickness of the OCL, minimizing the threshold current density, are obtained. The characteristic temperature of QD laser T_o is calculated for the first time considering carrier recombination in the OCL (barrier regions) and violation of the charge neutrality in QDs. The inclusion of violation of the charge neutrality is shown to be critical for the correct calculation of T_o. The characteristic temperature is shown to fall off profoundly with increasing temperature. A drastic decrease in T_o is shown to occur in passing from temperature conditions wherein the threshold current density is controlled by radiative recombination in QD's to temperature conditions wherein the threshold current density is controlled by radiative recombination in the OCL. The dependences of T_o on the root mean square of relative QD size fluctuations, total losses, and surface density of QDs are obtained     

Study on the dominant mechanisms for the temperature sensitivity ofthreshold current in 1.3-μm InP-based strained-layer quantum-welllasers

We study the basic physical mechanisms determining the temperature dependence of the threshold current (I_th) of InP-based strained-layer (SL) quantum-well (QW) lasers emitting at a wavelength of 1.3 μm. We show that I_th exhibits a different temperature dependence above and below a critical temperature T_c. It is indicated that T_c is the maximum temperature below which the threshold gain exhibits a linear relationship with temperature. We demonstrate that below T_c the Auger recombination current dominates the temperature dependence of I_th. On the other hand, above T_c a significant increase in both the internal loss and radiative recombination current in the separate-confinement-heterostructure region, which is mainly due to electrostatic band-profile deformation, is found to play a major role in determining the temperature sensitivity of I_th. On the basis of the comparison between the theoretical analysis and the experimental results, we conclude that the temperature dependence of the threshold current in 1.3-μm InP-based SL-QW lasers is dominated by different mechanisms above and below T_c     

Observation of reduced nonradiative current in 1.3-μmAlGaInAs-InP strained MQW lasers

We investigated experimentally the temperature dependence of the threshold current in 1.3-μm AlGaInAs-InP strained multiple-quantum-well lasers. We find that radiative recombination constitutes almost 100% of the threshold current up to 220 K and remains more than 70% even at 300 K. This results in a high characteristic temperature T₀     

Localized Auger Recombination in Quantum-Dot Lasers

We have calculated radiative and Auger recombination rates due to localized recombination in individual dots, for an ensemble of 10⁶ dots with carriers occupying the inhomogeneous distribution of energy states according to global Fermi-Dirac statistics. The recombination rates cannot be represented by simple power laws, though the Auger rate has a stronger dependence on the ensemble electron population than radiative recombination. Using single-dot recombination probabilities which are independent of temperature, the ensemble recombination rates and modal gain decrease with increasing temperature at fixed population. The net effect is that the threshold current density increases with increasing temperature due to the increase in threshold carrier density. The most significant consequence of these effects is that the temperature dependence of the Auger recombination rate at threshold is much weaker than in quantum wells, being characterized by a T₀ value of about 325 K. Observations of a strong temperature dependence of threshold in quantum dot lasers may have explanations other than Auger recombination, such as recombination from higher lying states, or carrier leakage.     

Temperature-humidity-bias behavior and acceleration factors fornonhermetic uncooled InP-based lasers

The stability of uncooled InP-based laser diodes in humid ambients was studied. Nonhermetic devices were aged at two different temperatures and humidities at a constant current and at one temperature and humidity at six different drive currents. For all nonhermetic devices failure occurred as a result of a large increase in the threshold current. The reverse leakage current for the failures did not increase when the threshold current increased, indicating that the change in threshold was a result of a change in reflectivity of one or both facets. The hermetic control group of devices aged under many of the same conditions showed a gradual increase in both the threshold current and slope efficiency. The median lifetimes as determined by assuming a device was a failure when the threshold current increased by 50% was strongly dependent upon humidity temperature and drive current. The lifetime data was fit to and equation of the form lifetime exp(-E_α/kT) exp(-B_RH [RH²]). The values of E_α and B_RH were 0.52 eV and 4.9×10^-4/%², respectively. The current drive data was fit to and expression of the form lifetime a exp(I^αI_op) where I_α as 0.09 h/mA. The lifetime dependence on current drive was modeled by assuming that the drive current caused a local temperature rise through thermal resistance. This local temperature rise then caused a decrease in the local humidity at the diode surface through an expression of the form %RH_diodeα exp (-5990[1/(T_r+T_ambient)-1/T_ambient ])where where T_r is the local temperature rise due to thermal impedance. Finally, we present our preliminary results on the reliability of nonhermetic SiO_x passivated lasers. These results indicate that such lasers can be made with sufficient reliability for use in telecommunications application     

1.3-μm CW lasing characteristics of self-assembled InGaAs-GaAsquantum dots

This paper presents the lasing properties and their temperature dependence for 1.3-μm semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-μm emission dots were successfully grown by the combination of low-rate growth and InGaAs-layer overgrowth using molecular beam epitaxy. 1.3-μm ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25°C with a realistic cavity length of 300 μm and high-reflectivity coatings on both facets. The internal loss of the lasers was evaluated to be about 1.2 cm^-1 from the inclination of the plots between the external quantum efficiency and the cavity length. The ground-level modal gain per dot layer was evaluated to be 1.0 cm^-1, which closely agreed with the calculation taking into account the dot density, inhomogeneous broadening, and homogeneous broadening. The characteristic temperature of threshold currents T₀ was found to depend on cavity length and the number of dot layers in the active region of the lasers. A T₀ of 82 K was obtained near room temperature, and spontaneous emission intensity as a function of injection current indicated that the nonradiative channel degraded the temperature characteristics. A low-temperature study suggested that an infinite T₀ with a low threshold current (~1 mA) is available if the nonradiative recombination process is eliminated. The investigation in this paper asserted that the improvement in surface density and radiative efficiency of quantum dots is a key to the evolution of 1.3-μm quantum-dot lasers     

Theory of the temperature dependence of the threshold current of an InGaAsP laser

The threshold current of an InGaAsP laser is calculated, where the radiative emission, reflection and absorption losses, and Auger recombination are considered. Moreover, the enhancement of the threshold carrier density at high temperatures is an important point. A mechanism for this enhancement is discussed. Then we obtain an excellent agreement with the measured temperature dependence of the threshold current, in particular the To-values for T≷TBand the break point TB. The reason for this break point is that the radiative recombination dominates for T < TB, whereas the strongly temperature dependent valence band Auger process becomes more and more important for T > TB. It is this process which causes the strong increase of the threshold current in the room temperature range.     

俄歇复合对应变量子阱激光器阈值电流的影响

通过考虑不同因素对压应变和张应变量子阱激光器阈值电流和特征温度的影响,得到了俄歇复合和非俄歇复合对阈值电流起主要作用的转变温度Tc,小于Tc时,主要是非俄歇复合;大于Tc时,主要是俄歇复合,而且张应变量子阱激光器转变温度要比压应变量子阱激光器的转变温度要高;张应变量子阱激光器与压应变量子阱激光器相比,阈值电流更低,特征温度更高。     

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     

A macroscopic model of nonlinear constitutive relations insuperconductors

A macroscopic model is proposed for nonlinear electromagnetic phenomena in superconductors. Nonlinear constitutive relations are derived by modifying the linear London's equations. The superelectron number density as a function of applied macroscopic current density, n _s(J), is derived from a distribution of electron velocities at a certain temperature T. At temperature T≠0 K, the function n_s(J) has a smooth variation near the macroscopic critical current density J_c. Agreement has been found between this n _s(J,T) model and the temperature dependence of n_s in the two-fluid model. The nonlinear conductivities σ_s(J) and σ_n(J) are obtained from the London's equation with the modified n_s(J) function. Nonlinear resistance R(I), kinetic inductance L_k(I) and surface impedance Z_s(I) in thin wire, slab, and strip geometries are calculated     

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     

Evidence of the importance of Auger recombination for InGaAsP lasers

The temperature dependence of Auger recombination in InGaAsP can be described by two regions, one with a slow increase of the Auger coefficient and one with a strong increase. This behaviour is similar to that of the threshold current of an InGaAsP laser. In particular, the slope of the temperature curve of the Auger coefficient changes at T = 255 K, which is exactly the break point temperature of the threshold current. Auger recombination therefore seems to be the most important cause for the temperature dependence of the threshold current in InGaAsP lasers.     

Temperature dependence of lasing characteristics forlong-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Data are presented on the temperature dependence of 1.3-μm wavelength quantum-dot (QD) lasers. A low-threshold current density of 90 A/cm² is achieved at room temperature using high reflectivity coatings. Despite the low-threshold current density, lasing at the higher temperatures is limited by nonradiative recombination with a rapid increase in threshold current occurring above ~225 K. Our results suggest that very low threshold current density (⩽20 A/cm ²) can be achieved at room temperature from 1.3-μm QD lasers, once nonradiative recombination is eliminated     

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T ³ in the case of Auger recombination.     

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.     

High reliability InGaP/GaAs HBT

Excellent long term reliability InGaP/GaAs heterojunction bipolar transistors (HBT) grown by metalorganic chemical vapor deposition (MOCVD) are demonstrated. There were no device failures (T=10000 h) in a sample lot of ten devices (L=6.4 μm ×20 μm) under moderate current densities and high-temperature testing (J_c=25 kA/cm ², V_ce=2.0 V, Junction Temp =264°C). The dc current gain for large area devices (L=75 μm ×75 μm) at 1 kA/cm² at a base sheet resistance of 240 ohms/sq (4×10 ¹⁹ cm^-3@700 Å) was over 100. The dc current gain before reliability testing (L=6.4 μm ×10 μm) at 0.8 kA/cm² was 62. The dc current gain (0.8 kA/cm²) decreased to 57 after 10000 h of reliability testing. The devices showed an f_T=61 GHz and f_max=103 GHz. The reliability results are the highest ever achieved for InGaP/GaAs HBT and these results indicate the great potential of InGaP/GaAs HBT for numerous low- and high-frequency microwave circuit applications. The reliability improvements are probably due to the initial low base current at low current densities which result from the low surface recombination of InGaP and the high valence band discontinuity between InGaP and GaAs     

1.5 μm wavelength distributed reflector lasers with verticalgrating

A 1.5 μm wavelength distributed reflector laser, consisting of a distributed Bragg reflector rear facet and a distributed feedback region, was realised using deep-etching technology. A low threshold current of I_th=12.4 mA and a high differential quantum efficiency of η_d=42% from the front facet was achieved with a submode suppression ratio of 33 dB (I=2.4 I_th) for a fifth-order grating, 220 μm long and 6 μm wide device at room temperature     

The influence of interface grading on threshold current density of (near) visible DH(Ga,Al)As lasers

The effect of interface grading around the active layer in DH (Ga, Al) As near-visible lasers (lambda_{L} approx 780nm) has been investigated for Ge and Sn as p- and n-type dopants. The combination of graded transition layers with a rather high Al and Ge concentration gives rise to a high effective interface recombination velocity (S lsim 4000cm/s) due to carrier loss in the highly Ge-doped p-Ga0.55Al0.45As cladding layer. The chemical widthWmin{90}max{10}of the transition layers is determined by SIMS and SAES and found to range between 50 and 2.5 nm. The latter extremely steep interfaces have been grown in a novel LPE growth system. The threshold current density and its temperature sensitivity, in terms of the exponential relationshipJ_{th}(T) = J_{0} exp (T/T_{0})improve significantly with abrupt junctions. From this material 5 μm proton-bombarded stripe lasers with a threshold current of ∼90 mA and aT_{0} = 120K at 780 nm have been fabricated.     

Improving InAs double heterostructure lasers with betterconfinement

The authors have conducted a theoretical study of InAs double heterostructure lasers. Carrier leakage due to drift current is shown to be the main mechanism of the injected carriers in lasers fabricated to date. Reduction of carrier leakage is shown to be possible by using wider bandgap lattice-matched material as the cladding layers. Increased optical confinement is also required to achieve the lowest possible threshold current, which strongly affects the highest lasing temperature achievable. An InAs double heterostructure employing AlAs_0.16Sb_0.84 as the cladding material is proposed. Simulation on this structure indicates that its threshold current density will be dominated by Auger recombination for most of the temperature range below 300 K, the estimated highest lasing temperature