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.     

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 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.     

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。     

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.     

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.     

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.     

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.     

Evidence for large monomolecular recombination contribution tothreshold current in 1.3 μm GaInNAs semiconductor lasers

The spontaneous emission, L, through a window in the substrate electrode of 1.3 μm GaInNAs MQW lasers was studied as a function of current, I, and temperature, T Close to room temperature, a characteristic temperature at threshold T,(L) T was observed as expected for band-to-band recombination in ideal quantum well devices. However, T ₀(I_th)≃T/3 indicating other processes occur. Analysis of the variation of L with I, reveals that monomolecular recombination contributes more than 50% to the total current at threshold and also that some Auger recombination may be present     

Threshold characteristics of λ=1.55 µm InGaAsP/InP heterolasers

Temperature dependences of the threshold characteristics of InGaAsP/InP quantum well (QW) lasers have been studied. The main contribution to the threshold current is made by the thresholdless Auger recombination. The observed power-law temperature dependence of the threshold current is explained by the predominance of the thresholdless Auger recombination in QWs over the threshold Auger process.     

Hot electrons and holes in MOSFET's biased below the Si—SiO2interfacial barrier

This work presents an investigation of low-voltage hot carrier injection in submicrometer size MOSFET's showing that for both electrons and holes it can take place even when the maximum energy to be gained by the applied field is less than the Si-SiO2interfacial barrier height. In the case of electrons, it is also shown that the injection process, due to Auger recombination at low applied drain-to-source voltages (VDS), is well described by the lucky-electron model (LEM) as soon as VDSexceeds the threshold for this to become applicable.     

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。     

Losses in GaInAs(P)/InP and GaAlSb(As)/GaSb lasers--The influence of the split-off valence band

GaInAs(P)/InP and GaAlSb(As)/GaSb are interesting material systems for long wavelength optical fiber communication. However lasers fabricated from these materials exhibit a substantially higher temperature dependence of the threshold current than GaAs/ GaAlAs lasers ("T0-problem"). lntervalence band absorption and CHSH-Auger-recombination have been suggested as two possible causes for the strong temperature dependent losses in long wavelength lasers. Both mechanisms, if present, should lead to a population of the split-off valence band. In GaInAsP/InP lasers, we have studied this population by directly observing the radiative high-energy recombination of electrons with holes in the split-off valence band. In the case of the band structure of GaAlSb(As), the band gap energy E0is close or equal to the spin-orbit splitting energy Δ0, which favors hole-Auger recombination and intervalence band absorption, as confirmed by our experimental results.     

Temperature dependence of the effective coefficient of Auger recombination in 1.3 μm InAs/GaAs QD lasers

Semiconductor laser heterostructures containing five and ten sheets of InAs/GaAs QDs on GaAs substrates, with an emission wavelength of ～1.3 μm, have been studied. Dependences of the nonradiative lifetime and effective Auger coefficient in QDs are obtained from an analysis of temperature and current dependences of the efficiency of spontaneous radiative recombination. The zero-threshold Auger recombination channel in QDs is shown to dominate at low (below 200 K) temperature, whereas at higher temperatures the quasithreshold channel becomes dominant. The effective 3D Auger coefficient is estimated in the approximation of a spherical QD, and a good agreement with the experimental data is 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     

高温CW半导体激光器的阈值电流

用载流子速率方程分析了高温CW半导体激光器(LD)阈值电流(I_(th))与温度(T)的关系.数值计算结果分别给出了与T有关的腔内损耗、双分子复合和俄歇过程以及载流子泄漏效应对I_(th)的贡献大小.     

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     

Recombination in small-gap Pb1−xSnxTe

Instrinsic and extrinsic recombination mechanisms in small-gap Pb_1−xSn_xTe are investigated by means of stationary and non-stationary laser-excited photoeffects, carried out under conditions with weak as well as strong deviation from equilibrium. A straightforward analysis of radiative recombination within the Kane type two-band model is given and supported by absorption measurements. This analysis is combined with a treatment of Auger recombination based on the parameters determined from the photoeffects. The conclusion is drawn that at high carrier concentrations (equilibrium or non-equilibrium) strong competition between radiative and Auger recombination takes place. The consequences for the threshold current of double hetero-junction lasers are outlined.     

The temperature dependence of internal parameters of disc laser diodes InAs/InAsSbP

For disc lasers based on the InAs/InAsSbP heterostructure with a generation wavelength of 3.03–3.06 μm, the internal quantum yield of luminescence and rates of radiative and nonradiative recombination in a temperature range of 85–120 K are determined. It is established that as the temperature increases, the relative contribution of the rate of nonradiative recombination to the density of the threshold current increases from 89.9 to 92.8%. It is shown that the most probable mechanisms of nonradiative transitions in the InAs/InAsSbP disc heterolasers can be the CHCC and CHSH Auger processes with involvement of phonons. Coefficients of total losses for two experimentally observed generation bands are determined, and the maximum level of the internal optical losses is estimated. The figure of merit of the resonator of the InAs/InAsSbP disc heterolaser is ～10⁴.     

Promotion of radiative recombination in GaAs1—XPxby N-ion implantation

As a means of promoting radiative recombination in GaAs1-xPx, nitrogen doping by ion implantation has been evaluated. When the sample is impanted at room temperature, poor results are obtained. However, when the sample is heated up to 350°C during implantation, and annealed at 800°C for 1 h, photoluminescence spectra are obtained similar to those of GaAs1-xPxwith N incorporated during growth. For indirect-bandgap GaAs1-xPx(x = 0.52), the integrated intensity at 77 K of the implanted sample is more than 1000 times larger than that of an unimplanted sample. This shows that under appropriate conditions implanted N atoms are substituted for P atoms and become isoelectronic traps. This trap, under the proper annealing conditions, can enhance radiative recombination significantly.