Measurement of radiative and auger recombination rates in p-type InGaAsP diode lasers

Carrier lifetimes and spontaneous emission rates are reported for InGaAsP diode lasers. For active layers Zn-doped in the range 1?2 × 1018/cm3 the radiative recombination constant B is 0.8 × 10?10 cm3/s and the nonradiative constant C is 0.9 × 10?28 cm6/s for a Cnp2 Auger process. For lightly doped lasers the Auger model alone cannot explain the data.     

Lifetime broadening in GaAs-AlGaAs quantum well lasers

Experimental observations of spontaneous emission spectra from GaAs-AlGaAs quantum well lasers shown that spectral broadening should be included in any realistic model of laser performance. A model of the lifetime broadening due to intraband Auger processes of the Landsberg type is described and developed for the case of electron-electron scattering in a 2-D system. The model is applied to the calculation of gain and spontaneous emission spectra and gain-current relationships in short-wavelength GaAs-AlGaAs quantum well lasers, and the results are compared with those obtained using both a fixed intraband scattering time and one that varies as n^-1/2, where n is the volume injected carrier density     

Light saturation of InGaAsP-InP LED's

The saturation behavior of the spontaneous light-current characteristic of InGaAsP (lambda = 1.3 mum) lasers and light emitting diodes are investigated as a function of injection level and temperature. For carrier injection levels below that at which optical gain is observed, it is shown that a nonradiative Auger recombination mechanism is consistent with the observed saturation behavior of the spontaneous emission intensity of lasers. Further evidence of the importance of Auger recombination at these low injection levels is provided by the dependence of the nonradiative component of the measured carrier lifetime (τA) on injection level (n) where it is found thattau_{A}^{-1} propto n^{2.1}. For injection levels above that required to achieve optical gain we report the direct observation of superlinear emission due to single pass gain in edge emitting LED's. The onset of this superluminescence at low temperatures (T < 200K) is found to correspond with the onset of saturation of the spontaneous emission from the sides. These results show that both Auger recombination and superluminescence should be taken into account when the electrooptical characteristics of InGaAsP LED's are calculated.     

Large-signal dynamic model of the DFB laser

A computer model is proposed to analyze the characteristics of distributed feedback (DFB) lasers. The model is based on time-dependent coupled wave equations, with spontaneous emission taken into account. In order to avoid uncertain phase factors in spontaneous emission, a method of converting field equations to power equations in a matrix format before computation is introduced. The steady-state LI curve and transient response to the pulse excitation are calculated in the λ/4 phase-shifted DFB lasers. The longitudinal variations of the carrier and photon densities as well as of the refractive index are considered in the model     

Analysis of diode laser properties

An analytic model of diode lasers applicable to both the lasing and the nonlasing states is described. For these homogeneously broadened devices, spectral envelope widths for TE00and TM00modes are related to power in each modal family and are shown to depend critically on spontaneous emission coupling into the transverse modes. Thus, lasers with real-refractive index waveguiding (and associated weak spontaneous emission coupling) operate single longitudinal mode above threshold, whereas gain-guided devices run multimode. After connecting gain and spontaneous emission, a charge conservation equation, containing optical power in the form of a stimulated emission term, pumping current, spontaneous emission, and spectral width, is derived. These equations are then demonstrated to suffice for determination of the completeLversusIcharacteristic. For lasers in which both charge and mode confinement exist, such as the buried heterostructure (BH) and channelled-substrate narrow stripe (CNS) types, it is shown that both TM00power and spectral envelope width approach limiting values at threshold, whereas TE00mode power grows in conjunction with TE00spectral envelope narrowing.     

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.     

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.<>     

Effects of high density pumping on relaxation oscillations and mode spectra in lasers

Effects of high density pumping on relaxation oscillations and mode spectra are investigated in LiNdP4O12(LNP) lasers. It is shown that high density pumping reduces the spatial population inhomogenuity, which is due to periodic inversion saturation by a first lasing mode in the crystal, and results in spontaneous single longitudinal mode oscillations even at high excitation rates. Physical interpretations are given for single-mode operations on the basis of Auger recombination (annihilation) process for 1.048 and 1.32 μm quantums in LNP lasers. An effective diffusion parameter of excited states is shown in an increase with absorbed pump power density through the Auger process. Observed relaxation oscillation waveforms, which disagreed with the traditional laser dynamic theory, are found to be explained well by the rate equations, including the effective diffusion constant.     

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     

Spontaneous emission efficiency of compressively strained 1.5 mu m MQW lasers

The spontaneous emission efficiency of 1.5 mu m compressively strained MQW lasers was found to be higher than that of comparable unstrained devices. The activation energy for Auger recombination was higher in the strained devices. Both effects were explained in terms of a reduction in the hole mass by strain.<>     

Electroluminescence of InAs/InAs(Sb)/InAsSbP LED heterostructures in the temperature range 4.2–300 K

The electroluminescence of InAs/InAsSbP and InAsSb/InAsSbP LED heterostructures grown on InAs substrates is studied in the temperature range T = 4.2–300 K. At low temperatures (T = 4.2–100 K), stimulated emission is observed for the InAs/InAsSbP and InAsSb/InAsSbP heterostructures with an optical cavity formed normal to the growth plane at wavelengths of, respectively, 3.03 and 3.55 μm. The emission becomes spontaneous at T > 70 K due to the resonant “switch-on” of the CHHS Auger recombination process in which the energy of a recombining electron–hole pair is transferred to a hole, with hole transition to the spin–orbit-split band. It remains spontaneous up to room temperature because of the influence exerted by other Auger processes. The results obtained show that InAs/InAs(Sb)/InAsSbP structures are promising for the fabrication of vertically emitting mid-IR lasers.     

Experimental and Theoretical Study of InAs/InGaAsP/InP Quantum Dash Lasers

We present a combined theoretical and experimental analysis of InAs/InGaAsP/InP quantum dash lasers. Calculations using an 8 band k.p Hamiltonian show that electron states, due to the low effective mass and small conduction band offsets, are not confined in the dash in the case of dash-in-a-well structures and are only weakly confined in dash-in-a-barrier structures. The shape of the dashes leads to an experimentally observed enhancement of spontaneous emission (SE) and therefore of gain for light polarized along the dash long axis, with the measured SE enhancement in excellent agreement with the theoretical calculations. An analysis of the variation of the integrated spontaneous emission rate with total current and with temperature reveals that, despite the reduced dimensionality of the active region, the threshold current of these lasers, and its temperature dependence, remain dominated by Auger recombination.      

Gain nonlinearity and its temperature dependence in bulk- andquantum-well quaternary lasers

Spectrally resolved measurements of unclamped spontaneous emission above threshold in 1.3 μm InGaAsP bulk double heterostructure and compressively strained multiquantum-well lasers are analyzed using steady state rate equations. Both types of structures are characterized by nonlinear gain coefficients in the range of (2.7-3.0)×10^-17 cm³ at 20°C. The nonlinear gain coefficient decreases with increasing temperature due to thermionic emission of carriers out of the active region and decreasing differential gain. The former effect was found to be more pronounced in quantum-well lasers. Excellent agreement with the rate equation based model is obtained     

Theoretical studies of UV-preionized transverse discharge KrF and ArF lasers

A theoretical model has been developed to examine the behavior of UV preionized, fast transverse discharge, rare-gas halide lasers. The model integrates the time dependent circuit equations for the discharge, the kinetic equations for the important atomic and molecular species and electrons, and the equations describing the growth of the spontaneous and stimulated emission. Results of KrF and ArF are compared with those in a companion experimental paper by Sze and Loree. The effects of various self-absorption mechanisms in the laser media are discussed, along with the possible impact of several uncertainties regarding the fundamental processes occurring in such lasers.     

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     

Spatio-temporal dynamics of light amplification and amplifiedspontaneous emission in high-power tapered semiconductor laseramplifiers

We investigate the spatio-temporal light field dynamics in high-power semiconductor lasers with continuous-wave optical injection. The amplification processes that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially dependent gain and refractive index variations. Those are shown to be determined by dynamic interactions between the light fields and the active charge-carrier plasma. This microscopic light-matter-coupling is described by a spatially resolved microscopic theory based on Maxwell-Bloch-Langevin equations taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and noise. Results of our numerical modeling visualize the dynamic spatio-spectral beam shaping experienced by the propagating light in amplifiers of tapered geometry. This reveals the microscopic physical processes that are responsible for the particular amplitude and spatial shape of the light beam at the output facet     

Q-switched semiconductor diode lasers

Diode lasers with an intracavity electroabsorption modulator have been operated with full on/off modulation at rates of 3 GHz. In addition, modulation of the lasers has been shown up to a detector-limited frequency of 6 GHz. A new model of these devices, which includes amplified spontaneous emission and high gain is developed in this paper. A quasi-static gain approximation is introduced and the dynamics of the electron and photon population are modeled by three coupled nonlinear difference equations which can be numerically solved with very little computation time. The model predicts the possibility of a new mode ofQ-switched operation with the capacity for repetition rates of tens of gigahertz and binary pulse position modulation at rates of the order of 10 Gbits/s.     

Calculated spontaneous emission factor for double-heterostructure injection lasers with gain-induced waveguiding

The fraction of spontaneous emission going into an oscillating laser mode has been calculated. It is shown that this fraction strongly depends on the strength of astigmatism in the laser output beam. Therefore the spontaneous emission factor in planar stripe lasers with narrow stripe is in the order of 10^-4and by one order of magnitude larger than in injection lasers with a comparable active layer volume and with a built-in index waveguide. It is shown that the spontaneous emission factor is approximately proportional to the solid angle of laser radiation and nearly independent of the transverse active layer dimensions. Owing to the large spontaneous emission factor, the spectral width of narrow planar stripe lasers is significantly broader compared to narrow stripe lasers with a built-in index waveguide. In addition the large spontaneous emission coefficient also yields a much stronger damping of relaxation oscillations.     

Spontaneous emission, scattering, and the spectral properties ofsemiconductor diode lasers

The effect of spontaneous emission on the above-threshold spectral output of 1.3-μm semiconductor diode lasers with internal scattering centers is examined. It is found that spontaneous emission masks the effect of scattering on the spectral properties of diode lasers. The spectral output of lasers with large amounts of spontaneous emission tend to be less affected by internal scattering than lasers with small amounts of spontaneous emission