MQW Lasers Research Articles

Gain characteristics of 1.55-μm high-speed multiple-quantum-well lasers

We describe the important characteristics of high-speed p-doped compressively strained MQW lasers obtained from comprehensive below-threshold DC measurements. Results of gain and differential gain versus wavelength and carrier density are verified by above-threshold resonance measurements. Measurement-derived design curves of gain, differential gain, and linewidth enhancement factor allow device optimization for high speed and low chirp. >

High performance InGaAsP/InP strained-layer MQWlaserswith reversed-mesa ridge-waveguide structures

Compressively-strained InGaAsP/InP MQW lasers with a simple reversed-mesa ridge-waveguide structure attain 300 mW output and high temperature lasing operation up to 165°C.

Analysis of gain in determining T/sub 0/ in 1.3 μm semiconductor lasers

Rapid decrease of differential gain has been determined to dominate the temperature dependence of threshold current in 1.3-/spl mu/m multiquantum well and bulk active lasers giving rise to low values of T/sub 0/. Extensive experimental characterization of each type of device is described. Results are presented for the dependence of gain on chemical potential and carrier density as a function of temperature. The data indicate the important role of the temperature-insensitive, carrier density dependent chemical potential in determining differential gain. Modeling of the temperature dependence of threshold carrier density in MQW and bulk active lasers based on a detailed band theory calculation is described. The calculated value of T/sub 0/ depends on the structure of the active layer, e.g., multiquantum well versus bulk. However, the calculated values are substantially higher than measured. >

Tapered InGaAs/GaAs MQW laserswith carbon modulation-dopingand reduced filamentation

Highly localised carbon doping is demonstrated within the active region of strained InGaAs/GaAs MQW lasers. As predicted by numerical beam propagation simulations, the smaller linewidth enhancement factor arising from the combination of strain and p-doping leads to reduced filamentation in tapered laser structures, as compared to devices fabricated from otherwise identical epilayer structures containing undoped active regions.

High-power and high-efficiency1.3 µm InAsP compressively-strained MQW lasersat high temperatures

A high output power of 37 mW and high slope efficiency of more than 0.55 W/A at 90°C has been obtained by using 1.05 µm InGaAsP barrier layers with optimised composition for 1.3 µm InAsP compressively-strained MQW laser diodes.

Reduced intermodulation distortion in 1300 nm gain-clamped MQW laser amplifiers

A 1300 nm gain-clamped DFB multiple quantum well laser amplifier with negligible pass band ripple, 20 dB fiber to fiber gain, and 10 dB reduction in gain saturation is demonstrated. The remaining gain saturation is attributed to longitudinal hole burning. After some modifications the reduction in gain saturation is improved to more than 30 dB for an input signal having the same polarization state as the lasing mode. From these experiments and a theoretical analysis it is concluded that there is a potential for realizing highly linear 1300 nm CATV semiconductor laser amplifiers using gain-clamping with less intermodulation distortion than today's directly modulated linear semiconductor lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low threshold current and high output power operationfor 1.5 µmGRINSCH strained MQW laser diode

A low threshold current of 1.8 mA and large slope efficiency of 0.30 mW/mA were obtained using 1.5 mu m GRINSCH strained MQW laser diodes. High-temperature operation was confirmed, and the threshold current at 80 degrees C was 5.0 mA with a slope efficiency of 0.18 mW/mA. The device had a short carrier lifetime of less than 1.55 ns.

A comparative study of temperature sensitivity of InGaAsP and AlGaAs MQW lasers using numerical simulations

We used numerical simulation to compare the temperature sensitivity of an InGaAsP MQW laser emitting at 1.55 /spl mu/m and an AlGaAs MQW laser at 0.82 /spl mu/m. By artificially changing the InGaAsP laser gradually into a structure similar to the AlGaAs laser, we gained quantitative insight into how each material or structural parameter causes the relatively low T/sub 0/ of the InGaAsP MQW laser. Using a typical MQW structure we demonstrated the relative importance of parameters involving Auger recombination, current leakage over the quantum barrier, optical confinement and band offset. We found that if these parameters were made the same as the AlGaAs laser, the T/sub 0/ of the InGaAsP laser was even better than that of the AlGaAs laser. Our numerical simulation confirmed that the Auger recombination is the main cause of low T/sub 0/ in MQW InGaAsP lasers. We also discovered that thermal current leakage over the barrier and Auger recombinations are correlated with each other and both factors must be improved to increase the T/sub 0/ of InGaAsP lasers to that of AlGaAs lasers. >

Improved performance from pseudomorphic InyGa/sub 1-y/As-GaAs MQW lasers with low growth temperature AlxGa/sub 1-x/As short-period superlattice cladding

We present results from In/sub 0.35/Ca/sub 0.65/As-GaAs 4 QW lasers whose Al/sub 0.8/Ga/sub 0.2/As binary short-period superlattice (SPSL) cladding layers were grown at either 700/spl deg/C or 620/spl deg/C. The threshold current densities (J/sub th/) are /spl sim/3 times smaller for the lasers whose AlGaAs cladding layers were grown at 620/spl deg/C. At the same time, the internal differential quantum efficiency (/spl eta//sub i/) increases from 60% to 70%. We attribute the lower J/sub th/ and increased /spl eta//sub i/ to a significant decrease in the concentration of point defects in the MQW active region, consistent with the observed improvement of the diode ideality factor. Temperature-dependent photoluminescence (PL) results suggest that these nonradiative recombination centers are related to point defects recently observed with Raman scattering. Ridge lasers grown with low-temperature SPSL Al/sub x/Ga/sub 1-x/As have achieved 3-dB modulation bandwidths of 24 GHz at record low bias currents of only 25 mA. >

High-power and wide-temperature-range operations of InGaAsP-InP strained MQW lasers with reverse-mesa ridge-waveguide structure

A new structure for an InP-based ridge-waveguide laser is demonstrated. It has a reverse-trapezoid-ridge shape that offers reduced threshold current and smaller series resistance suitable for wide-temperature-range and high power operations. A 1.3 μm strained InGaAsP-InP MQW laser with the new ridge structure demonstrated over 200 mW output under a 440 mA injected current. Low threshold (<25 mA) and high efficiency (>0.3 W/A) operation was also achieved under 90/spl deg/C for 1.53 μm strained MQW lasers.

High spectral tuning range of a modelocked InGaAs/InGaAsP MQW laser diode due to light hole gain contribution

We report on modelocking of an external cavity multi quantum well semiconductor laser with an extremely wide spectral tuning range. Pulse widths in the order of 30 ps were obtained spectrally tunable from 1448 to 1563 nm. The broadening of the gain spectrum is experimentally shown to be due to the additional contribution of the electron n=1 to the light hole n=1 transition. This conclusion is supported by numerical calculations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discussion of the linewidth enhancement factor alpha of GaAs/GaAlAs quantum well lasers

The fundamental contributions of optical interband transitions and the plasma effect of free carriers to the linewidth enhancement factor alpha of Ga(Al)As quantum well lasers has been discussed with respect to the dependence on the main laser structure parameters: confinement profile, number of quantum wells and well width. The results show clearly that alpha increases with carrier density. Particularly, in SQW-SCH laser structures with thin quantum wells, alpha is enlarged drastically by the plasma effect due to the necessary high threshold carrier densities. Both, the use of a GRINSCH structure or a MQW laser design reduce the free carrier component of alpha considerably. Furthermore, only a weak dependence of the alpha factor on the number of quantum wells is found in the case of MQW lasers. Finally, a comparison of alpha -simulations and measurements on SQW-GRINSCH and SQW-SCH BCRW laser structures shows a good agreement.

High performance strained MQW lasers at1.3 µm by MOVPE using arsine generator system

For safety reasons an arsine generator system (ASGS), operating on demand, was used instead of arsine cylinders as the source for MOCVD. Excellent compensated strained multiquantum well (S-MQW) laser devices were realised for the first time with this generator. The threshold current density for infinite cavity length is 84 A/cm/sup 2/ per well. This value is among the best values reported for this type of structure.

Differential gain, refractive index, and linewidth enhancement factor in high-speed GaAs-based MQW lasers: influence of strain and p-doping

The addition of strain and p-doping in high-speed GaAs-based MQW lasers are assessed experimentally in terms of their potential for both increasing the differential gain, /spl part/g//spl part/N, and reducing the modulus of the differential refractive index, |/spl part/n//spl part/N|, in order to decrease the linewidth enhancement factor, /spl alpha/. The increased differential gain with strain alone is found to be offset by a corresponding increase of |/spl part/n//spl part/N|. The further addition of p-doping, on the other hand, simultaneously increases /spl part/g//spl part/N and decreases |/spl part/n//spl part/N|, yielding a substantial reduction in /spl alpha/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impedance, modulation response, and equivalent circuit of ultra-high-speed In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers with p-doping

On-wafer measurements of the frequency-dependent impedance, modulation response, and RIN power spectra of ultra-high-speed p-doped In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers are presented and analyzed. The experimental results are shown to be accurately modeled by an equivalent circuit which accounts for both the carrier transport/capture dynamics and the junction space-charge capacitance. We find that the carrier escape time out of the QW's in our laser structure is much larger. Than the carrier capture time, and therefore the interplay between carrier capture and re-emission is not affecting the high-speed modulation dynamics. On the other hand, the absolute values of both the carrier capture time and the space-charge capacitance still limit the modulation bandwidth. >

A frequency response model in multiquantum well lasers with unequilibrium carrier transport

A carrier transport model to explain the high-frequency response in high-speed MQW lasers is described. The ambipolar approximation, which is unsuitable for dealing with the high-speed carrier dynamics in MQW structures, was not adopted for small-signal analysis. The carrier transport effect can be characterized by four time constants: the electron transport time, τbmn; the hole transport time, τbmp; the electron escape time, τwbn; and the hole escape time, τwbp. The frequency response was interpreted as the sum of the constant response term due to the fast electron current and the roll-off term due to the slow hole transport time. The ratio of the electron contribution to the total response was proportional to the ratio of electron contribution to the total differential gain, ξ, and reciprocally proportional to χn0 = 1 + τbmn/τwbn. The value of ξ was calculated to be about 0.5 for typical MQW lasers. The roll-off frequency is mainly determined by . The ratio χp0 = 1 + τbmp/τwbp affects the resonant frequency and the damping rate in the high-bias condition.

Structure-dependent threshold current density for CdZnSe-based II-VI semiconductor lasers

The optical gain and threshold current density of CdZnSe-based semiconductor lasers are calculated theoretically with strain and quantum confinement effects taken into account. Both diffusion and drift components are incorporated into the calculation of leakage current. Optimized structures are obtained for CdZnSe-based lasers with different structures through minimizing the threshold current density. A minimum current density of about 200 A/cm/sup 2/ is obtained for a Cd/sub 0.2/Zn/sub 0.8/Se/ZnS/sub 0.06/Se/sub 0.94//Zn/sub 0.75/Mg/sub 0.25/S/sub 0.42/Se/sub 0.58/ modified MQW laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of GaInP/AlGaInP compressive strained multiple-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-/spl Aring/-thick quantum wells, the threshold characteristics are degraded.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulse width tunable subpicosecond pulse generationfrom anactively modelocked monolithic MQW laser/MQWelectroabsorption modulator

Actively modelocked pulses are generated from a 1.59 mu m MQW laser integrated with an MQW electroabsorption modulator driven at the monolithic cavity frequency. The pulse width is controlled from 39 ps to 0.55 ps by changing the inverse bias voltage applied to the electroabsorption modulator and by linear pulse compression using a fibre. >

Monolithic GaAs/AlGaAs optical transmitter circuitusing a single growth step

A strained GaAs/AlGaAs/InGaAs MQW laser has been monolithically integrated with GaAs MESFETs in a differential pair configuration to form a transmitter circuit. The structure used a single epitaxial growth step in which the laser was grown on top of the MESFET. The circuits operate with bandwidths as high as 3.4 GHz.