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 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.     

Low-Temperature Nonthermal Population of InAs–GaAs Quantum Dots

Measurements of the unamplified spontaneous emission spectra from 80 K to 350 K of a dot ensemble show clear evidence for increased population of higher lying states in the inhomogeneous distribution as the temperature is reduced from 200 K to 80 K, indicating a nonthermal population at low temperature and confirming that the recombination processes are localized in individual dots. These conclusions are supported by modeling an inhomogeneous ensemble of $2times 10^{6}$ dots. From simultaneous measurements of optical gain, our data show that the increase in threshold current density with decreasing temperature below about 200 K (which is commonly observed) is due to increased population of higher lying states associated with the transition to nonthermal behavior.      

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.     

Measurement of radiative and nonradiative recombination rates in InGaAsP and AlGaAs light sources

A small signal method is used to measure the carrier lifetime as a function of injected carrier density, and the results are used to determine the radiative and nonradiative recombination rates for AlGaAs LED's and 1.3 μm InGaAsP lasers. For AlGaAs LED's the radiative recombination constant decreases with injected carrier density and the rate equation contains a small nonradiative Cn³term. The low internal efficiency of 1.3 μm InGaAsP lasers is found to be primarily caused by two factors: a radiative coefficientB(n)which strongly decreases with the injected carrier density, and CHHS Auger recombination having a recombination coefficient of1-2 times 10^{-29}cm⁶/s. A recombination term representing carrier leakage is observed in some devices, but it is not the principal cause of low internal efficiency.     

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.     

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     

Hot phonons and Auger related carrier heating in semiconductoroptical amplifiers

We have directly measured the carrier temperature in semiconductor optical amplifiers (SOAs) via spontaneous emission and we demonstrate an unexpectedly high carrier temperature. The direct correlation of the temperature increase with the carrier density suggests Auger recombination as the main heating mechanism. We have developed a model based on rate equations for the total energy density of electrons, holes, and longitudinal-optical phonons. This model allows us to explain the thermal behavior of carrier and phonon populations. The strong heating observed is shown to be due to the combined effects of hot phonon and Auger recombination in the valence band. We also observe an evolution of the Auger process, as the density is increased, from cubic to square dependence with coefficients C₃ = 0.9 10^-28 cm⁶ s^-1 and C₂ = 2.4 10^-10 cm³ s^-1. This change is explained by the hole quasi-Fermi level entering the valence band     

Auger recombination effect on threshold current of InGaAsP quantum well lasers

The Auger recombination effect on the threshold current of the InGaAsP quantum well (QW) laser is studied theoretically. All possible transitions between the quantized subbands of two-dimensional carriers are taken into account in evaluating the radiative process with thek-selection rule and the Auger process. The calculated threshold current agrees well with the reported experimental results for 1.07 μm InGaAsP QW lasers. The Auger component of the threshold current and its temperature dependence strongly depend on the QW structure, resulting in the necessity for an elaborate QW structure design, although both cannot be optimized at the same time. A design procedure is elucidated for a structure which gives the lowest threshold current density for the 1.07, 1.3, and 1.55 μm InGaAsP QW lasers.     

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     

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)     

镓铟砷／铝铟砷 QWLD中俄歇复合及其对T0的影响

修正了现行俄歇复合率的公式，并用之分析了晶格匹配ＧａＩｎＡｓ／ＡｌＩｎＡｓ异质材料系统在有无量子尺寸效应情况下的俄歇复合随载流子浓度和温度变化的行为。发现其阈值电流密度随温度的变化行为可分为特征温度不同的相邻两个温区，在较高温区，量子尺寸效应作用不大，在较低温区，量子尺寸效应反而降低了Ｔ０，并对此意外的现象提出初步的解释。     

Experimental study of Auger recombination, gain, and temperaturesensitivity of 1.5 μm compressively strained semiconductorlasers

The effect of strain on Auger recombination has been studied using the differential carrier lifetime technique in both lattice matched InGaAs-InP and compressively strained quaternary quantum wells. It is found that Auger recombination is reduced in strained devices. The transparency carrier density and differential gain of both lattice matched and strained devices have been obtained by gain and relative intensity noise measurement. A reduction of the transparency carrier density is observed in the strained device. However, no differential gain increase is seen. The temperature sensitivity of the threshold current density of both lattice matched and strained devices has been fully studied. Physical parameters contributing to the temperature sensitivity of the threshold current density have been separately measured, and it is shown that the change in differential gain with temperature is a dominant factor in determining the temperature sensitivity of both lattice matched and strained devices     

Band-to-band auger effect in long wavelength multinary III-V alloy semiconductor lasers

Band-to-band Auger effects and radiative recombination rates are theoretically compared for long wavelength multinary III-V compound semiconductor lasers. Stern's band model and matrix element are used for the calculation of gain coefficient and radiative recombination rate. Overlap integrals for Auger processes are obtained by ak cdot pperturbation method. Approximate statistical weight function is used, which includes the weakly degenerate effect. It is found that the Auger effect involving excited split-off band (CHSH process) is dominant when bandgap Egis greater than split-off gap Δ, while the Auger effect involving excited conduction band (CHCC process) predominates over others whenE_{g} < Delta. When Egis comparable to or slightly larger than Δ, the total Auger effect is weak and the quantum efficiency is recovered. This explains the experimentally reported low threshold current in AlGaAsSb and GaInAsSb lasers at about 1.8 μm. In all the possible III-V lasers, the quantum efficiency is reduced to less than 5 percent for wavelengthslambda > 2.2 mum at room temperature and forlambda > 4.4 mum at 77 K, respectively. The calculated values of Auger currents include an error of factor two or three, mainly caused by the ambiguity in band parameters.     

Threshold characteristics of an IR laser based on deep InAsSb/AlSb quantum well

The basic threshold characteristics of a semiconductor IR laser based on a heterostructure with deep InAs_0.84Sb_0.16/AlSb quantum wells (QWs) have been studied. The threshold carrier densities and threshold current densities of radiative and Auger recombination (AR) were found. It is shown that at certain QW parameters the AR rate is strongly (by several orders of magnitude) suppressed. In this case, the emission wavelength falls within the interval 2–3.5 μm, which corresponds to the mid-IR spectral range. The internal quantum efficiency of emission at the lasing threshold was calculated and its dependence on the QW width within the AR suppression range was demonstrated. The laser structure was optimized with respect to the number of QWs.     

Radiative and nonradiative recombination law in lightly doped InGaAsP lasers

We analyse data relating to radiative and nonradiative recombination in a 1.3 ?m InGaAsP laser operating below threshold. The results show that with a lightly doped active region the radiative recombination coefficient decreases with increasing carrier concentration in accordance with previous theoretical results. Further, they indicate that the Auger nonradiative recombination is relatively small.     

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).     

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.     

Dominance of auger recombination in InGaAsP light emitting diode current-power characteristics

Output power saturation in 1.3-µm InGaAsP light emitting diodes with various active layer thickness has been investigated experimentally in a wide temperature range. Nonradiative recombination current with strong injected carrier density dependence, which is responsible for saturation, was found to be proportional to active layer thickness and almost independent of temperature under constant injected carrier density conditions. External quantum efficiency at a constant injected carrier density was found to be independent of active layer thickness. These results indicate strongly that Auger recombination is the dominant nonradiative process in InGaAsP light sources.     

The performance of double active region InGaAsP lasers

The light-current characteristic and temperature behavior of the double-carrier-confinement (DCC) InGaAsP laser are shown to be largely determined by Auger recombination. The carrier distributions in the two active regions, especially their relative fractions, play a major role in device behavior. A self-consistent, comprehensive numerical laser model is used to analyze a set of devices showing that superlinearity and possibly bistability are due to saturable absorption in the second active region and that a high characteristic temperature is usually tied with a higher threshold current density because of substantial Auger recombination rates in this type of device