A suppression mechanism of Auger recombination effects in strainedquantum wells induced by local negative curvature of the energy bandstructure

An analytical method has been developed to calculate distribution of carriers that undergo CHHS Auger recombinations in semiconductors. From this approach, it is further discovered that holes with a local negative effective mass are, statistically, not favored in the CHHS Auger recombination process. As extended regions in valence subbands of compressively strained quantum well structures possess a negative curvature-and thus a local negative hole effective mass-this mechanism is identified to be a significant factor that suppresses Auger recombination effects in compressively strained quantum well laser diodes. This suppression mechanism is also observed and confirmed by recent Monte Carlo calculation results     

Auger recombination in strained quantum wells

A nonthreshold mechanism for Auger recombination of nonequilibrium carriers in quantum wells with strained layers is investigated theoretically. It is shown that the dependence of the Auger recombination rate on the magnitude of the strain and the height of the heterobarriers for electrons and holes can be analyzed only by calculating the overlap integrals between initial and final particle states microscopically. In quantum wells with strained layers the presence of strain affects qualitatively and quantitatively the electron-hole overlap integral. The dependence of the Auger recombination rate on the quantum well parameters, the magnitude of the stress, and temperature are analyzed for heterostructures based on InGaAsP/InP and InGaAlAs/InP. Fiz. Tekh. Poluprovodn. 31, 358–364 (March 1997)     

Theoretical study of auger recombination processes in deep quantum wells

The basic processes and mechanisms of Auger recombination of nonequilibrium carriers in a semiconductor heterostructure with deep InAs_0.84Sb_0.16/AlSb quantum wells (QWs) are analyzed. It is shown that a zero-threshold Auger recombination process involving two heavy holes predominates in sufficiently narrow QWs, and a resonant process involving two electrons is dominant in wide QWs. The range of QW widths at which the Auger recombination is suppressed in a given structure to the greatest extent (suppression region) is determined. In this case, the threshold process involving two electrons remains the basic nonradiative recombination process, with its probability being several orders of magnitude lower than those for the zero-threshold and resonant mechanisms. In turn, the zero-threshold mechanism involving two electrons is totally impossible in the heterostructure under study because of the large conduction-band offset (which markedly exceeds the energy gap). Also, the range of emission wavelengths that corresponds to the suppression region is estimated. It is shown that the interval calculated belongs to the mid-IR range.     

Dynamics of photoluminescence and recombination processes in Sb-containing laser nanostructures

The dynamics of interband photoluminescence has been studied at various temperatures and excitation levels in structures with quantum wells based on InGaAsSb alloys and barriers based on AlGaAsSb and AlInGaAsSb alloys. The lifetimes of optically injected charge carriers in quantum wells at various temperatures and levels of optical excitation have been experimentally determined. An increase in the recombination rate in structures with deeper InGaAsSb/AlGaAsSb quantum wells for electrons is attributed to manifestation of resonant Auger recombination. The Auger recombination brings about heating of electrons and holes in lower subbands of dimensional quantization. The temperature of charge carriers in the course of Auger recombination is estimated using the equation for balance of power with accumulation of nonequilibrium optical phonons taken into account. The studied structures were used to fabricate lasers of two types with lasing wavelength of approximately 3 μm; it is shown that the use of a quinary alloy as the material for the barrier leads to an improvement in the characteristics of the lasers.     

Size effects in Auger recombination for InGaAs quantum-wirestructures

A theoretical investigation of Auger recombination in lattice-matched InGaAs/InGaAlAs quantum-wire structures is presented. The valence band structure is calculated by using a four-band Luttinger-Kohn Hamiltonian. CHCC, CHHH, CHHL and CHHS Auger processes are considered with the excited carrier being either in a confined (bound) state of the quantum wire, or an unconfined (unbound) state. The model uses Fermi statistics as well as a revaluation of the Coulomb interaction overlap integral for the calculation of the Auger recombination rate. Bound-unbound Auger processes are proven to be important nonradiative recombination mechanism in quantum-wire systems. It is also found that the Auger coefficient is much more sensitive to the well width in quantum-wire structures than in quantum-well structures     

Auger recombination in long-wavelength strained-layer quantum-wellstructures

A model calculation of Auger recombination in strained-layer InGaAs-InGaAlAs and InGaAs-InGaAsP quantum-well structures is presented as an extension of an empirical Auger theory based on the effective mass approximation. The valence band effective masses around k_∥=0 are calculated by using a six-band Luttinger-Kohn Hamiltonian and the quasi-Fermi levels are determined with a self-consistent Poisson-Schrodinger solver under the effective mass approximation. Three basic Auger processes are considered with the excited carrier being in a bound state of the quantum well, as well as an unbound state. The empirical model includes Fermi statistics as well as a revaluation of the Coulomb interaction overlap integral in the Auger recombination rate. Bound-unbound Auger transitions are proved to be an important nonradiative recombination mechanism in strained-layer quantum-well systems. Our calculations of Auger coefficient are in reasonable agreement with the experimental data     

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。     

Factors limiting current gain in power transistors

The combined effect of sidewall injection, bandgap narrowing, and Shockley-Hall-Read and Auger recombination in determining emitter efficiency in n-p-n power transistor structures is demonstrated by utilizing a two-dimensional transistor model. The relative importance of each of these effects is calculated as a function of emitter junction depth, emitter surface doping, and injection level. It is shown that in a practical transistor design the reduction in emitter efficiency due to the increased injection of holes into the emitter, resulting from bandgap narrowing caused by heavy doping, is not dominated by the emitter sidewall. Auger recombination is seen to be especially important when bandgap narrowing is present. Enhanced Auger-type recombination is due both to increased minority carrier injection in the emitter as well as current crowding effects. The predictions of the model are compared with results of the measurement of current gain versus current level characteristics on existing devices.     

Auger recombination rates in compressively strainedInxGa1-xAs/InGaAsP/InP(0.53⩽x⩽0.73) multiquantum well lasers

The authors have experimentally determined Auger recombination rates in compressively strained In_xGa_1-xAs/InGaAsP/InP MQW lasers for the first time. The Auger recombination rates were derived from the measured turn-on delay times during large-signal modulation of single-mode lasers. The Auger coefficient increases from 5±1×10^-30 to 13±1×10^-30 cm⁶ s^-1 as the indium composition in the quantum well active region, x, increases from 0.53 to 0.73     

A “cold” InP-based tunneling injection laser withgreatly reduced Auger recombination and temperature dependence

We have measured the Auger recombination rates in an InP-based quantum well tunneling injection laser from large signal modulation experiments. Measured values of the Auger coefficient, C_o=1.2±0.6×10^-29 cm⁶ s^-1 at 283 K, are a factor of over 10² smaller than those measured in similar multiple quantum well separate confinement heterostructure lasers. In effect, the tunneling injection mechanism keeps the carriers “cold” even at high injection levels. A maximum value of T_o=70 K is measured in the tunneling injection laser compared to 50 K for conventional quantum well structures,     

Analysis of radiative efficiency of long wavelength semiconductor lasers

An analysis of the spontaneous emission efficiency of laser diodes which yields C/B/sup 3/2/ where C and B are the Auger and radiative recombination coefficients, respectively, is proposed as a measure of the fundamental band structure and is applied to the temperature and pressure dependence of unstrained 1.5 mu m quantum well lasers.<>     

Impact ionization resonance and auger recombination in Hg1 - xCdxTe (0.6 ≤ x ≤ 0.7)

The purpose of this paper is the study of the impact ionization and the Auger recombination in Hg1-xCdxTe avalanche photodiodes, with0.6 leq x leq 0.7. Forx sim 0.7it is shown that the spin orbit splitting Δ is lower than the bandgap energy Egso that impact ionization is initiated by holes from the Split-off valence band. Forx sim 0.6, Delta sim E_{g}, the rate of the Auger recombination is maximum, corresponding to a resonant impact ionization and to a maximum ratiok = beta / alphawhere α and β are, respectively, the impact ionization coefficient for electrons and holes.     

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.     

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.     

On the radiative recombination and tunneling of charge carriers in SiGe/Si heterostructures with double quantum wells

For SiGe/Si(001) epitaxial structures with two nonequivalent SiGe quantum wells separated by a thin Si barrier, the spectral and time characteristics of interband photoluminescence corresponding to the radiative recombination of excitons in quantum wells are studied. For a series of structures with two SiGe quantum wells different in width, the characteristic time of tunneling of charge carriers (holes) from the narrow quantum well, distinguished by a higher exciton recombination energy, to the wide quantum well is determined as a function of the Si barrier thickness. It is shown that the time of tunneling of holes between the Si_0.85Ge_0.15 layers with thicknesses of 3 and 9 nm steadily decreases from ~500 to <5 ns, as the Si barrier thickness is reduced from 16 to 8 nm. At intermediate Si barrier thicknesses, an increase in the photoluminescence signal from the wide quantum well is observed, with a characteristic time of the same order of magnitude as the luminescence decay time of the narrow quantum well. This supports the observation of the effect of the tunneling of holes from the narrow to the wide quantum well. A strong dependence of the tunneling time of holes on the Ge content in the SiGe layers at the same thickness of the Si barrier between quantum wells is observed, which is attributed to an increase in the effective Si barrier height.     

Comparison of Auger recombination in GaInAs-AlInAs multiple quantum well structure and in bulk GaInAs

Carrier lifetime has been measured in GaInAs-AlInAs multiple quantum well structures and in thick GaInAs samples for local carrier densities between2 times 10^{17}and5 times 10^{19}cm^-3. Carrier lifetime and Auger recombination are found to be very close (±20 percent) in the two structures. The Auger limited T0values calculated for DH and MQW lasers are found to be, respectively, 93 and 170 K. Optimization of the quantum well laser as a function of the number of wells in the active region is discussed.     

Numerical simulation of evolution of electron-hole avalanches and streamers in silicon in a uniform electric field

Numerical simulation of origination and evolution of streamers in Si is performed for the first time. It is assumed that an external electric field E ₀ is constant and uniform, the avalanche and streamer are axially symmetric, and background electrons and holes are absent. The calculations have been performed in the context of the diffusion-drift approximation with impact and tunneling ionization, Auger recombination, and electron-hole scattering taken into account. The most realistic values of the ionization and recombination rates, diffusion coefficients, and drift mobilities of electrons and holes have been used. It is shown that the features of evolution of avalanches and streamers are generally consistent with the result obtained previously for a hypothetic semiconductor with equal kinetic coefficients for electrons and holes. Asymmetry of these coefficients (mostly, the impact-ionization coefficients) manifests itself only at the initial stage of evolution. However, with time, two exponentially self-similar streamers are formed, differing only in the sign of charge of fronts and directions of their propagation. Empirical dependences of the main parameters of streamers on E ₀ in the range of 0.34–0.75 MV/cm have been derived for this most important stage of evolution.     

Auger effect in GaSb quantum well lasers

The Auger recombination effect in GaSb quantum well lasers is discussed. A formula for the calculation of the CHSH Auger rate in quantum well structures is presented, which can be applied to the material where the bandgap is almost the same as the split-off gap. Using this formula, the quantum efficiency of the GaSb quantum well laser is calculated and compared to those of conventional double heterostructure lasers. It is found that the quantum efficiency of the GaSb quantum well laser can be improved to values higher than 50 percent in the wavelength range of1.5-1.8mum.     

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     

Influence of temperature on Auger recombination lifetime in In1?xGaxAs materials

The influence of temperature and Ga composition on Auger recombination lifetime in n-type and p-type In1-xGaxAs materials is investigated through the simulation, assuming the concentrations of electrons and holes are 1017 cm-3 and 1018 cm-3, respectively. The results show that the temperature has little influence on Auger recombination lifetime of In1-xGaxAs materials at x<0.3. However, it has a great impact when x>0.3 and the effect is more obvious at a lower temperature. Moreover, Auger ...