Temperature dependence of threshold current of GaAs quantum well lasers

The radiative recombination rate in a quantum well structure is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs quantum well laser has low temperature sensitivity (T0 ? 330 K for T > 300 K).     

Temperature dependence of the threshold current in 1.55-μmstrain-compensated multiquantum-well distributed-feedback lasers

The temperature dependent threshold current and spectral output characteristics of InP-based 1.55-μm distributed-feedback (DFB) ridge InGaAsP MQW lasers made by metal-organic vapor phase epitaxial growth and regrowth, electron-beam lithography and grating formation, and reactive ion etching (RIE) have been characterized. Single-mode operation and T₀ as high as 120 K at room temperature and below are measured. The high value of T₀ is predominantly attributed to the tunnel injection design incorporated in the active region     

Temperature dependence of the threshold current for InGaAlP visiblelaser diodes

The temperature dependence of the threshold current for InGaAlP visible-light laser diodes was investigated from the standpoint of gain-current characteristics. The dependence of the light output power versus the current characteristic on the cavity length was evaluated for a 40-μm-wide InGaP-InGaAlP broad-stripe laser in the temperature range between -70 and 90°C. The threshold-current density dependence on the cavity length shows that a linear-gain approximation is suitable for this system. A minimum threshold-current density of 860 A/cm² was achieved at room temperature with a cavity length of 1160 μm. The internal quantum efficiency decreased in the temperature range higher than -10°C, which affected the excess threshold-current increase and the decrease in the characteristic temperature at this temperature range     

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.     

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     

Temperature dependence of threshold current for a quantum-well heterostructure laser

The threshold current density, J_th, of a quantum-well laser diode is calculated taking into account the quasi-two-dimensional nature of the heterostructure. The calculated value of J_th(T) for a quantum-well laser diode is found, in agreement with experiment, to be less temperature sensitive than that of a conventional double heterojunction laser. The step-like densities of states and the perturbed (hot) carrier distribution of a quasi-two-dimensional structure are responsible for the weaker temperature dependence. Supporting data on quantum-well Al_xGa_1-xAsGaAs heterostructure laser diodes grown by MO-CVD are presented showing that in the conventional expression J_th(T) = J_th(0) exp (T/T₀), T₀ can be as high as ～ 437°C.     

Pressure dependence of threshold current and carrier lifetime in 1.55 ?m GaInAsP lasers

The threshold current and carrier lifetime were measured as a function of pressure in oxide stripe and IRW GaxIn1?xAsyP1?y 1.55 ?m lasers. The results indicate that intervalence band absorption is a more important loss mechanism than the combined effects of Auger recombination, loss over the barrier and recombination through defects.     

Well width dependence of gain and threshold current in GaAlAs single quantum well lasers

The optical gain of single quantum well GaAs/GaAlAs laser diodes is studied theoretically. The model uses a nok-selection rule and Fermi statistics to obtain the gain coefficient expression. Gain-current characteristics are then reported and allow comparison of structures with well widths between 50 and 400 Å. Comparison is also made to previous models which use a strictk-selection rule. Then theoretical threshold current densities are calculated for typical single quantum well lasers where the optical confinement is performed using a five-layer slab waveguide. They are shown to be relatively insensitive to the well width as long as Lzis larger than 80 Å. Comparison between two different structures shows that optical confinement plays a critical role for optimizing the threshold Current and should be carefully studied, especially if thek-selection rule is relaxed.     

Temperature dependence of threshold and electrical characteristics of InGaAsP-InP d.h. lasers

Measurements are reported of the electrical characteristics and temperature dependence of threshold current of InGaAsP-InP d.h. lasers (? = 1.3 ?m). Analysis of the I dV/dI characteristics of these devices indicates that drift leakage of carriers from the active region is not responsible for the high temperature sensitivity of threshold in this material system.     

Increased threshold for the first-order lateral mode lasing in low-ridge waveguide high power QW lasers

A self-consistent two-dimensional model is extended to include two-mode operation and is applied to study the characteristics of ridge-waveguided high power InGaAs-GaAs quantum-well lasers. This work provides physical insight into the most recent experimental result that use low-ridges and thin p-claddings to give high single lateral mode output and a low threshold.     

Nonmonotonic threshold size dependence of buried-post verticalcavity lasers

The dependence on cavity width of the threshold gain of buried-post vertical-cavity surface emitting lasers (VCSELs) is analyzed using a 2-D model. In contrast to former reports on other VCSEL structures such as the oxide-apertured structure, nonmonotonic behaviors appear clearly both in the dependencies of threshold and resonance frequency of the present structure. By considering cavity modes as a superposition of many waveguide modes propagating parallel to multilayers, it is revealed that the physical mechanism causing this nonmonotonicity is the interference effect among these component waveguide modes. The interference causes the center of gravity of the lateral energy-flow of the superimposed field to wiggle through the multilayer waveguide, and thus, depending on the cavity size, either to hit or to miss the reflecting index-step structure of the cavity sidewall which, accordingly, makes the lateral energy confinement either efficient or loose, resulting in a low- or high-loss cavity. The oscillatory threshold dependences of the fundamental and the first higher-order modes appear out of phase, which results in even larger oscillatory variation in their threshold difference. This indicates that, for stabilization of fundamental-mode oscillations in the present cavity structure, cavity size should be one of discrete optimal values rather than simply smaller. Besides the buried post structure, the oxide-apertured structure and the dielectrics-passivated post-cavity structure are also analyzed using the 2-D model and compared with experimental data     

Low threshold current densities for II-VI lasers

II-VI-semiconductor-based, green-light-emitting laser diodes with significantly improved characteristics are reported. Threshold current densities of 42 A/cm² are obtained. Novel contacts also lead to a 25% reduction in the threshold voltage and to an increased device lifetime by a factor of 24 as compared to previous results     

半导体激光器阈值电流的精确测量

一、引言阈值电流是半导体激光器的重要参数之一。通常用测量半导体激光器的输出光功率——电流(PI)特性曲线、观察远场或近场图样的变化以及光谱随电流的变化等来确定阈值,但误差较大。本文用测量半导体激光器调制光信号的二次谐波来确定阈值电流。理论和实验都表明用谐波测量法测定半     

Temperature dependence of threshold current in (GaAl)as double-heterostructure lasers with emission wavelengths of 0.74-0.9µm

The threshold-current variation with temperature has been measured for Ga1-xAlxAs double-heterostructure (DH) lasers with AlAs mole fraction in the active layerxof 0.08 and 0.2, and with several heterojunction step heightsDeltax. The threshold-temperature coefficient Jth(350 K)/Jth(300 K), which generally increases with decreasingDeltax, is found to be larger forx = 0.2than that forx = 0.08at the same value ofDeltax, and also to be larger for the lasers with smaller effective electron diffusion length in thePcladding layer, in the case ofx = 0.2. These characteristics are well explained by a model of carrier leakage due to unconfined carriers in the active layer. It is confirmed by a good fit of the experimental results with the calculated values that the electron leakage in theGammaconduction band of thePcladding layer dominates forx leq 0.1, but the hole leakage in theNcladding layer increases withxand becomes comparable in magnitude with the electron leakage atx sim 0.2.     

Temperature dependence of POPOP dye vapor lasers

The pure POPOP dye vapor is excited in a transverse geometry by an N2laser and the output power of the laser is measured as a function of temperature and intensity of the exciting laser. The threshold temperature is about 310°C and the maximum output power is obtained at around 390°C. The threshold intensity of the exciting laser is about 0.3 MW/cm²and the output power is almost linearly dependent on the intensity as far as experimentally observed. The shift of the oscillation wavelength is observed with increasing temperature and the central wavelength of the broad-band laser can be tuned from 385 to 402 nm by the selection of the vapor density. Theoretical results calculated from rate equations which are dependent on time and space qualitatively agree with these experimental results. The effect of reflectance of the cavity on the output power is also discussed.     

Temperature dependence of POPOP dye vapor lasers

The pure POPOP dye vapor is excited in a transverse geometry by an N2laser and the output power of the laser is measured as a function of temperature and intensity of the exciting laser. The threshold temperature is about 310°C and the maximum output power is obtained at around 390°C. The threshold intensity of the exciting laser is about 0.3 MW/cm²and the output power is almost linearly dependent on the intensity as far as experimentally observed. The shift of the oscillation wavelength is observed with increasing temperature and the central wavelength of the broad-band laser can be tuned from 385 to 402 nm by the selection of the vapor density. Theoretical results calculated from rate equations which are dependent on time and space qualitatively agree with these experimental results. The effect of reflectance of the cavity on the output power is also discussed.     

Temperature dependence of the Gunn threshold in GaAs

Measurement of the temperature dependence of the threshold for transferred electron instabilities in GaAs gives (1/IP(300))×(dIP/dT=?2.4±0.2×10?3 K?1, independent of carrier concentration The threshold field decreases with decreasing T and depends on carrier concentration. Reasonable agreement is obtained with Monte Carlo calculations based on ?-L-X ordering.     

Structure-dependent threshold current density for CdZnSe-basedII-VI semiconductor lasers

The optical gain and threshold current density of CdZnSe-based semiconductor lasers are calculated theoretically with strain and quantum confinement effects taken into account. Both diffusion and drift components are incorporated into the calculation of leakage current. Optimized structures are obtained for CdZnSe-based lasers with different structures through minimizing the threshold current density. A minimum current density of about 200 A/cm² is obtained for a Cd_0.2Zn_0.8Se/ZnS_0.06Se_0.94 /Zn_0.75Mg_0.25S_0.42Se_0.58 modified MQW laser     

Quantum-dot lasers: Principal components of the threshold current density

Injection heterolasers based on quantum dots grown by molecular-beam epitaxy have been investigated. It is shown that the room-temperature threshold current density can be lowered to 15 A/cm² by decreasing the nonradiative recombination and increasing the degree of carrier localization. The density of states in structures with vertically coupled quantum dots was investigated by the electroabsorption method. Fiz. Tekh. Poluprovodn. 31, 1106–1108 (September 1997)