Analysis of differential gain in InGaAs-InGaAsP compressive andtensile strained quantum-well lasers and its application for estimationof high-speed modulation limit

A simplified model that furnishes an intuitive insight for the change in quantum-well (QW) laser gain due to QW strain and quantum confinement is presented. Differential gain for InGaAs-InGaAsP compressive and tensile strained multi-quantum-well (MQW) lasers is studied using the model. The comparison between the calculated and experimental results for lattice-matched and compressive strained MQW lasers shows that this model also gives quantitatively reasonable results. It is found that the variance-band barrier height strongly affects the differential gain, especially for compressively strained MQW lasers. The tensile strained MQW lasers are found to have quite high differential gain, due to the large dipole matrix element for the electron-light-hole transition, in spite of the large valence-band state density. Furthermore, a great improvement in the differential gain is expected by modulation p doping in the tensile strained MQW lasers. The ultimate modulation bandwidth for such lasers is studied using the above results     

High-performance λ=1.3 μm InGaAsP-InP strained-layerquantum well lasers

Compressively and tensile strained InGaAsP-InP MQW Fabry-Perot and distributed feedback lasers emitting at 1.3-μm wavelength are reported. For both signs of the strain, improved device performance over bulk InGaAsP and lattice-matched InGaAsP-InP MQW lasers was observed. Tensile strained MQW lasers show TM polarized emission, and with one facet high reflectivity (HR) coated the threshold currents are 6.4 and 12 mA at 20 and 60°C, respectively. At 100°C, over 20-mW output power is obtained from 250-μm-cavity length lasers, and HR-coated lasers show minimum thresholds as low as 6.8 mA. Compressively strained InGaAsP-InP MQW lasers show improved differential efficiencies, CW threshold currents as low as 1.3 and 2.5 mA for HR-coated single- and multiple quantum well active layers, respectively, and record CW output powers as high as 380 mW for HR-AR coated devices. For both signs of the strain, strain-compensation applied by oppositely strained barrier and separate confinement layers, results in higher intensity, narrower-linewidth photoluminescence emissions, and reduced threshold currents. Furthermore, the strain compensation is shown to be effective for improving the reliability of strained MQW structures with the quantum wells grown near the critical thickness. Linewidth enhancement factors as low as 2 at the lasing wavelength were measured for both types of strain. Distributed feedback lasers employing either compressively or tensile strained InGaAsP-InP MQW active layers both emit single-mode output powers of over 80 mW and show narrow linewidths of 500 kHz     

Measurements of the polarization dependence of the gain of strained multiple quantum well InGaAs-InP lasers

The polarization-dependent gain spectra of both tensile and compressive strain multiple-quantum-well (MQW) In/sub x/Ga/sub 1-x/As-InP lasers in a relatively large strain regime are presented. The results show that MQW lasers with tensile strain and an In concentration as low as 43% in the wells lase in a pure transverse magnetic (TM) mode rather than a transverse electric (TE) mode with a gain difference of 60-70 cm/sup -1/ at all the injection currents investigated. The peak gain for the TE mode is shifted toward shorter wavelengths from that of the TM mode, indicating that the emission is principally due to light hole-electron transition. The differential gain of the TM mode is about 1.5 times higher than that of the TE mode operation. Opposite phenomena were observed in the compressive strained MQW lasers.<>     

The effect of varying barrier height on the operationalcharacteristics of 1.3-μm strained-layer MQW lasers

This paper presents an empirical study of the effects that barrier layer composition has on the operational characteristics of 1.3-μm-wavelength InGaAsP-InP multiquantum-well (MQW) strained-layer ridge-waveguide lasers. A systematic empirical investigation of how this design choice affects practical device operation was undertaken by examining threshold current, efficiency, and modal gain as a function of temperature in five different laser structures. The results of these studies indicate that small barrier heights improve device performance, despite the loss of electronic confinement in the shallow conduction band quantum wells. Indeed, it appears that carrier uniformity in the MQW structure may be improved by carrier redistribution due to thermal or tunneling effects, which in turn enhances the operation of the low barrier height structures     

Low dispersion penalty and wide temperature range operation over120 K with 1.55 μm strained MQW-DFB laser module

STM 16 (2.488 Gbit/s) system operation over a wide DFB chip temperature range of more than 120 K (from -25°C to +95°C) is presented with dispersion penalty below 1 dB after transmission across 100 km standard fibre. DFB operation at 1.55 μm with a high sidemode suppression ratio of 40 dB is achieved within -40°C to +95°C. The lasers were realised using a BRS lateral structure and a quaternary InGaAsP MQW stack with six compressively strained quantum wells and a highly detuned DFB grating     

Analysis of GaInP/AlGaInP compressive strainedmultiple-quantum-well laser

We have analyzed GaInP/AlGaInP compressive strained MQW lasers, with theoretical calculation and experimental results. Our calculations of TE polarized gain, where the valence subband mixing and the heterobarrier leakage current are taken into account, are in good agreement with the experimental results. When a compressive strain of up to 0.5% is induced in the quantum wells, the density of states near the valence band edge is decreased, due to the reduction of heavy-hole and light-hole subband mixing. At the threshold condition, the compressive strain reduces not only the radiative recombination current, but also the hetero-barrier leakage current. Therefore, the threshold current is reduced, and its temperature dependence is found to be small, In the analysis, we also show that when larger compressive strain of more than 0.5% is induced in the 40-Å-thick quantum wells, the threshold characteristics are degraded     

Carrier transport effects in long-wavelength multiquantum-welllasers under large-signal modulation

Significant differences are observed between long-wavelength multiquantum-well (MQW) and bulk distributed-feedback (DFB) diode lasers in terms of their gain-switched dynamic performance. Through careful comparison of experimental and theoretical results, carrier transport is found to be particularly important in determining gain-switched operation     

The “gain-lever" effect in InGaAsP/InP multiple quantum welllasers

The gain-lever-effect has been assessed in both multiple quantum well (MQW) and bulk active region lasers having a range of lengths and split ratios in the top contact. Compared with a conventional single-contact laser, a 500-μm MQW FP device with a top-contact split ratio of 8:1 exhibited >15-dB improvement in AM efficiency and a signal-to-noise ratio improvement of 7.5 dB. With proper impedance matching, these figures may be improved. A reduced noise figure is obtained at the expense of dynamic range with an additional nonlinearity seen experimentally due to thermal and carrier leakage when compared with simulations carried out using a harmonic balance model. Used carefully, these gain-lever lasers are useful components for future analogue fiber-optic systems     

Microscopic simulation of the temperature dependence of static and dynamic 1.3-/spl mu/m multi-quantum-well laser performance

The temperature dependence of the performance of 1.3-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers is analyzed using detailed microscopic simulations. Both static and dynamic properties are extracted and compared to measurements. Devices with different profiles of acceptor doping in the active region are studied. The simulation takes into account microscopic carrier transport, quantum mechanical calculation of the optical and electronic quantum well properties, and the solution of the optical mode. The temperature dependence of the Auger coefficients is found to be important and is represented by an activated form. Excellent agreement between measurement and simulation is achieved as a function of both temperature and doping profile for static and dynamic properties of the lasers, threshold current density, and effective differential gain. The simulations show that the static carrier density, and hence the contribution to the optical gain, varies significantly from the quantum wells on the p-side of the active layer to those on the n-side. Furthermore, the modal differential gain and the carrier density modulation also vary. Both effects are a consequence of the carrier dynamics involved in transport through the MQW active layer. Despite the complexity of the dynamic response of the MQW laser, the resonance frequency is determined by an effective differential gain, which we show can be estimated by a gain-weighted average of the local differential gain in each well.     

Influence of free carrier plasma effect on carrier-inducedrefractive index change for quantum-well lasers

The influence of the free carrier component due to the plasma effect on carrier-induced refractive index change and its dependency on polarization for multiple-quantum-well (MQW) and bulk lasers are experimentally studied. The ratios of the component to the total index change, R_fc, are 0.6, 0.4, and 0.1 for 1.3-μm MQW, 1.3-μm bulk, and 0.8-μm MQW lasers, respectively. The TM/TE polarization ratios of the component, R_TMTE/, are 0.8 and 0.3 for 1.3-μm MQW and 0.8-μm MQW lasers. The relationship between the index change and the carrier overflow (to barrier and separate confinement heterostructure layers) for MQW lasers is also discussed. Large R_fc and R_TMTE/ for the 1.3-μm MQW laser result from the carrier overflow     

Effects of internal loss on power efficiency of mid-infraredInAs-GaInSb-AlSb quantum-well lasers and comparison with InAsSb lasers

Experimental studies of the lasing efficiency of optically pumped 4-μm GaInSb-InAs-AlSb multiple-quantum-well (MQW) lasers that emitted >1-W peak power/facet at 80 K indicated that internal loss is the main factor that limits the power output. The internal loss coefficient and internal quantum efficiency were determined by measuring the lasing efficiency versus temperature for devices of different facet reflectivities and lengths. The internal loss coefficient was found to increase from ~18 cm^-1 near 70 K to ~60-100 cm^-1 near 180 K, while the internal quantum efficiency remained constant at ~47% (or ~67% with the correction for the finite absorption of the active region) from 70 to 130 K. The increase of internal loss and the decrease of external quantum efficiency versus temperature were found very similar to those of double-heterostructure InAsSb-GaSb lasers and were similarly interpreted in terms of intervalence band carrier absorption. Extrapolation of power performance for improved devices with lower internal loss indicated that high-efficiency multi-watt quasi-CW output with a broad-area brightness of ~1 MW/cm².sterad is possible     

Pure strain effects in strained-layer multiple-quantum-well lasers

Pure effects of strain in strained-layer multiple-quantum-well (MQW) lasers are measured separately from quantum effects using Fabry-Perot (FP) lasers with the same well thicknesses but different strains. The differential gain and gain saturation coefficients and the K factors of the lasers are determined by measuring relative-intensity-noise (RIN) spectra with various bias conditions. The differential gain coefficient increases when the compressive strain increases. The gain saturation coefficient also increases with increasing compressive strain. The K factor increases slightly when the compressive strain increases because of the slight increase in the ratio of the gain saturation coefficient to the differential gain coefficient     

Strained-layer InGaAs(P) quantum well semiconductor lasers and semiconductor laser amplifiers

Progress in long-wavelength strained (compressive and tensile) InGaAs(P) quantum well semiconductor lasers and amplifiers for applications in optical fibre communication systems is reviewed. By the application of grown-in strain, device performance is considerably improved to such an extent that conventional bulk and unstrained quantum well active-layer devices are outperformed, while high reliability, similar to that of unstrained devices, is maintained.     

Strain-induced performance improvements in long-wavelength,multiple-quantum-well, ridge-waveguide lasers with all quaternary activeregions

A comparison between the performance of strained (1.5% compression) and unstrained multiple-quantum-well (MQW), ridge-waveguide lasers with identical geometrical structures and similar emission wavelengths is reported. Results show that significant improvements in the characteristic temperature (T₀), maximum output power, maximum operating temperature, and internal quantum efficiency can be obtained through the applications of strain. Accordingly, for lasers employing strained active regions, an improved characteristic temperature, T₀, of 85 K and high-maximum lasing temperature of 140°C were obtained under pulsed operating conditions. These values are the highest ever observed for long-wavelength lasers with all-quaternary strained MQW active regions     

GaAs和GaAs/AlGaAs多层量子阱中载流子的超快动力学(英文)

The ultrafast photoexcited carrier dynamics in bulk GaAs and GaAs/ AlGaAs multiple quantum well(MQW)structure has been studied using femtosecond laser pulse pump-probe techniques on the samples grown by MBE. A hot carrier cooling time of 1.5ps in MQW is measured at room temperature. Also, optical phonon emission at 33meV is observed in this sample. These results are found to be similar to that observed in bulk GaAs. A comparison of the hot carrier cooling rates for the two cases suggests that the infra-sub-band optical phonon scattering in MQW may play a dominant role in the cooling of highly excited hot carriers for the narrow wells. The experimental results agree well with that predicted by a simple infinite depth square-well model.     

100‐period, 1.23‐eV bandgap InGaAs/GaAsP quantum wells for high‐efficiency GaAs solar cells: toward current‐matched Ge‐based tandem cells

Major challenges for InGaAs/GaAsP multiple quantum well (MQW) solar cells include both the difficulty in designing suitable structures and, because of the strain‐balancing requirement, growing high‐quality crystals. The present paper proposes a comprehensive design principle for MQWs that overcomes the trade‐off between light absorption and carrier transport that is based, in particular, on a systematical investigation of GaAsP barrier effects on carrier dynamics that occur for various barrier widths and heights. The fundamental strategies related to structure optimization are as follows: (i) acknowledging that InGaAs wells should be thinner and deeper for a given bandgap to achieve both a higher absorption coefficient for 1e‐1hh transitions and a lower compressive strain accumulation; (ii) understanding that GaAs interlayers with thicknesses of just a few nanometers effectively extend the absorption edge without additional compressive strain and suppress lattice relaxation during growth; and (iii) understanding that GaAsP barriers should be thinner than 3 nm to facilitate tunneling transport and that their phosphorus content should be minimized while avoiding detrimental lattice relaxation. After structural optimization of 1.23‐eV bandgap quantum wells, a cell with 100‐period In_0.30GaAs(3.5 nm)/GaAs(2.7 nm)/GaAsP_0.40(3.0 nm) MQWs exhibited significantly improved performance, showing 16.2% AM 1.5 efficiency without an anti‐reflection coating, and a 70% internal quantum efficiency beyond the GaAs band edge. When compared with the GaAs control cell, the optimized cell showed an absolute enhancement in AM 1.5 efficiency, and 1.22 times higher efficiency with 38% current enhancement with an AM 1.5 cut‐off using a 665‐nm long‐pass filter, thus indicating the strong potential of MQW cells in Ge‐based 3‐J tandem devices. Copyright © 2013 John Wiley & Sons, Ltd.     

Pure effects of strain in strained-layer multiple-quantum-welllasers

The pure effects of strain in strained-layer InGaAs-InGaAsP multiple-quantum-well (MQW) Fabry-Perot (FP) lasers operating in the 1.5 μm region are measured separately from the quantum effects by using lasers whose active layer wells have the same thickness but different amounts of strain. The gain peak wavelengths of transverse electric (TE) and transverse magnetic (TM) modes and the difference between TE- and TM-mode gain peak wavelengths increase when compressive strain is introduced. The differential gain coefficient and the gain saturation coefficient of the lasers are determined by measuring relative intensity noise (RIN) spectra and are found to increase with increasing compressive strain. The K factors of the lasers are determined from the relationship between the damping constant and the resonant frequency square     

SPICE simulation for analysis and design of fast 1.55 μm MQWlaser diodes

A rate equation model for static and dynamic behavior of 1.55 μm InGaAsP multiquantum-well (MQW) semiconductor lasers has been developed. A three level scheme for the rate equations has been chosen in order to model carrier transport effects. The introduction of quasi-two dimensional (quasi-2-D) gateway states between unbound and confined states has been used to calculate, for each well independently, carrier density and gain, allowing to take nonuniform injection into account. Starting from the formal identity between a rate equation and a Kirchoff current balance equation at a capacitor node, the model has been implemented on a SPICE circuit emulator, SPICE has granted an easy handling of parasitics and opens the possibility of integration with electrical components. The model's parameters have been directly derived from a complete set of measurements on real devices. Thanks to this characterization and the model accuracy, we have obtained good agreement between simulations and experimental data. The model was finally used to improve both static and dynamic properties of MQW devices. Based on this optimization, compressive strained InGaAsP-InP MQW Fabry-Perot lasers were realized, achieving low threshold current, high efficiency, and more than 10 GHz of direct modulation bandwidth     

AlGaInP-GaInP compressively strained multiquantum-welllight-emitting diodes for polymer fiber application

We have studied the optical properties of the AlGaInP-GaInP light-emitting diodes (LED's), with a compressively strained multiquantum-well (CSMQW) active layer, emitting at 650 nm. It was found that by introducing a compressive strain into the MQW active layer, we can achieve a much faster operation speed and a higher output power. It was also found that a +0.33%, compressive strain can reduce the 10%-90% rise time and/or fall time from 50 to 15 ns. Furthermore, the +0.33% compressive strain can also increase the output power of the MQW AlGaInP-GaInP LED by more than 40%. Such a high operation speed and high output power LED is potentially useful in polymer-based optical fiber communication     

Improved performance of 2-μm GaInAs strained quantum-well laserson InP by increasing carrier confinement

We have fabricated and analyzed strained GaInAs quantum-well diode lasers emitting at wavelengths above 2 μm, grown by metal-organic chemical vapor phase epitaxy on InP substrates. To study the effect of carrier confinement on laser performance, lasers grown with nearly lattice matched ternary GaInAs barriers and quaternary GaInAsP barriers were compared. The use of quaternary barriers improves the device performance in terms of output power, emission wavelength, characteristic temperature, differential quantum efficiency, and power efficiency. Internal losses and internal quantum efficiency remain unchanged. At a heat sink temperature of 330 K index guided diode lasers with GaInAsP-barriers emitting at 2.092 μm showed a continuous-wave (CW) output power of 42 mW/facet