Conventional Double Heterostructure Lasers Research Articles

Waveguide properties of gallium, aluminum, and indium nitride heterostructures

The waveguide properties of double heterostructures constructed from nitrides of group-III elements are investigated. It is established that a maximum 8–10% AlN is sufficient (for limiting the optical mode inside the active region) in the solid solution of the wide-gap layer. The influence of light absorption in the wide-gap layers on the threshold current density of heterostructure lasers is taken into account. This form of light absorption is probably a decisive factor for heterostructures utilizing III-nitrides. A threshold current density at levels of the order of 10 kA/cm2 is expected for lasers utilizing such structures. Because of strong light absorption in the waveguide layer, the threshold current density for lasers with solitary quantum wells cannot be expected to be any lower than that of conventional double-heterostructure lasers. The threshold current density can be lowered to a few kA/cm2 in the case of lasers with a large number of quantum wells.

Compressively strained 1.3 mu m InAsP/InP and GaInAsP/InP multiple quantum well lasers for high-speed parallel data transmission systems

Turn-on delay times in the pulse response of compressively strained InAsP/InP double-quantum-well (DOW) lasers and GaInAsP/InP multiple-quantum-well (MQW) lasers emitting at 1.3 mu m were investigated. DQW lasers with 200- mu m cavity length and high-reflection coating achieved both a very low threshold current (1.8 mA) and a small turn-on delay time (200 ps), even under a biasless 30-mA pulse current. Compressively strained or lattice-matched GaInAsP MQW lasers and GaInAsP double-heterostructure (DH) lasers were also fabricated and compared. It was observed that the carrier lifetime was enhanced for InAsP DQW lasers and strained GaInAsP MQW lasers compared to the lattice-matched GaInAsP MQW lasers and conventional double-heterostructure lasers. To explain this increase in the carrier lifetime, the effect of the carrier transport on the carrier lifetime was studied. The additional power penalty due to the laser turn-on delay was simulated and is discussed. >

Carrier lifetimes and threshold currents in HgCdTe double heterostructure and multi-quantum-well lasers

The Auger and radiative combination carrier lifetimes in HgCdTe bulk and quantum-well structures, with band gaps in the wavelength range 2–5 μm, are calculated. The Auger recombination rate in a HgCdTe quantum well (QW) is shown to be significantly smaller than that in bulk material. Threshold current densities of HgCdTe double-heterostructure (DH) and multiquantum-well (MQW) lasers are calculated. In a HgCdTe DH laser, Auger recombination dominates the carrier loss at threshold. In a HgCdTe MQW laser, on the other hand, radiative recombination dominates the carrier loss. MQW lasers shown improved temperature performance over conventional DH lasers.

Effect of strain on the resonant frequency and damping factor in InGaAs/InP multiple quantum well lasers

The intensity noise of strained InxGa1−xAs/InP multiple quantum well (MQW) lasers is measured for three types of strain: tensile strain (x=0.48), no strain (x=0.53), and compressive strain (x=0.65). From a comparison between the measured noise power spectral density and the theoretical one, the resonance frequency and the carrier damping factor of each type of lasers are calculated. Although compressive strained MQW lasers show abot 10% increase in resonance frequency compared to those of tensile strained and unstrained lasers, this increase is smaller than theoretically predicted. Most important, all three types of MQW lasers show about two to three times higher nonlinear gain saturation and lower maximum bandwidth than conventional double-heterostructure lasers. A solution to reduce this high damping is also discussed.

Degradation kinetics of GaAs quantum well lasers

Degradation-induced dark line defect growth velocities have been found to be inversely proportional to the operating temperature in quantum well lasers under current injection. A model has been developed, which considers the differing band structure and role of deep levels in quantum well structures as opposed to conventional double-heterostructure lasers. Our findings have significant implications for device yield since they suggest nontraditional screening strategies that recognize temperature as a decelerant for the sudden failure mode.

Spontaneous emission factor and waveguiding in GaAs/AlGaAs MQW lasers

The waveguiding properties of gain-guided GaAs multiple quantum-well (MQW) lasers are investigated. Near- and far-field measurements reveal that gain guiding is much stronger in the MQW lasers than in conventional double-heterostructure lasers. The index antiguiding, however, is of the same strength in both types of lasers. Due to the altered lateral waveguiding, the astigmatism factor K is very low in the MQW lasers and has a value of K=3. As a consequence, MQW lasers exhibit very narrow far fields ( theta /sub 11/ degrees ), nearly single longitudinal mode operation with a sidemode suppression ratio of 1/10 and a low linewidth enhancement factor alpha =2.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral linewidth and resonant frequency characteristics of InGaAsP/InP multiquantum well lasers

The spectral linewidth and resonant frequency characteristics of 1.3- mu m InGaAsP/InP multi-quantum-well lasers grown by liquid-phase epitaxy were investigated and compared to those of the conventional double heterostructure (DH) lasers. A decrease in spectral linewidth and an increase in resonant frequency f/sub r/ with decreasing well thickness were observed. Moreover, the linewidth enhancement factor alpha was reduced to approximately 2 for well thicknesses of less than approximately 200 AA, while that of the DH laser was approximately 6. An f/sub r/ of 9 GHz, which is twice as large as that of conventional DH lasers, was achieved at an optical power of 5.3 mW/facet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Filamentation in conventional double heterostructure and quantum well semiconductor lasers

A wave-optical model is used to investigate filamentation of the optical field in conventional double heterostructure and quantum well semiconductor lasers. The field is propagated by the Crank-Nicholson method, and the gain model is based on a semiclassical laser theory that contains the effects of cross relaxation due to electron-electron and electron-phonon collisions. The model predicts that for broad-area devices, quantum well lasers are less affected by filamentation than conventional double heterostructure lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Linewidth enhancement factor in InGaAsP/InP multiple quantum well lasers

The linewidth enhancement factor α in an InGaAsP/InP multiple quantum well (MQW) laser has been determined from the spontaneous emission spectra below threshold. It is demonstrated that the measured value of α in the MQW laser is appreciably smaller than that in a conventional double heterostructure laser as expected from theoretical calculations.

High-power (710 mW cw) single-lobe operation of broad area AlGaAs double heterostructure lasers grown by metalorganic chemical vapor deposition

Broad area, conventional double heterostructure lasers were fabricated by metalorganic chemical vapor deposition. Continuous wave output power level of 710 mW and stable, single-lobed far-field patterns with a beam divergence as narrow as 2.1° (2.2 times diffraction limit) at 50 mW and 2.9° at 200 mW for a 50-μm-wide laser were obtained.

Phase locked narrow zinc diffused stripe laser arrays

Phase locked operation of an array of narrow diffused stripe conventional double heterostructure laser elements grown by metalorganic chemical vapor deposition is reported. Six-element arrays (length 356 μm) show threshold currents of 33 mA per stripe and peak power outputs of at least 160 mW per facet with total external differential quantum efficiencies of 33%. Complex near-field patterns are shown which result from two opposing mechanisms involved in guiding of the lateral modes. Three major lobes in far-field patterns, which correspond to expected patterns for the lateral modes of gain guided arrays, are described.

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 of 1.5-1.8\mu m.

Homogeneous gain saturation in GaAs/AlGaAs quantum well lasers

We have studied the dynamical behavior of laser emission in optically pumped GaAs/AlGaAs lasers with picosecond time resolution. We find a saturation of the spontaneous emission above threshold and a homogeneous reduction of carrier lifetime down to about 70 ps. These data suggest a homogeneous gain saturation in GaAs/AlGaAs quantum well lasers, similar to conventional double heterostructure lasers.

Theory of gain, modulation response, and spectral linewidth in AlGaAs quantum well lasers

We investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers. These include a basic derivation of the laser gain, the linewidth enhancement factor α, and the differential gain constant in single and multiple QW structures. The results reveal the existence of gain saturation with current in structures with a small number of wells. They also point to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.

Fabrication and performance characteristics of InGaAsP ridge-guide distributed-feedback multiquantum-well lasers

The fabrication and performance characteristics of InGaAsP ridge-guide distributed-feedback lasers with multiquantum-well active layers are reported. The lasers are 320 μm long and have four active wells (300 A thick). The lasers have threshold current 100 mA at 30°C, external differential quantum efficiency 0.1 mW/mA/facet at 30°C and To 60 K and can be operated in the same DFB mode up to 70°C. The measured frequency chirp is about a factor of 3 smaller than that for conventional double-heterostructure lasers. The smaller chirp should allow larger repeater spacing for high-bit-rate long-distance fibre transmission systems applications.

Long wavelength InGaAsP (λ∼1.3 μm) modified multiquantum well laser

The fabrication and performance characteristics of InGaAsP (λ∼1.3 μm) double channel planar buried heterostructure lasers with multiquantum well (MQW) active layers are reported. The MQW structure has λg∼1.3 μm InGaAsP active wells and λg∼1.03-μm InGaAsP barrier layers. The lasers have threshold current of ∼20 mA at 30 °C and external differential quantum efficiencies of ∼0.2 mW/mA/facet at 30 °C. The temperature dependence of threshold current is characterized by T0∼100 K both under electrical and optical pumping. The lasers have been operated to 110 °C and up to ∼30 mW/facet at 25 °C. The measured dynamic linewidth under modulation is ∼2 smaller than that for conventional double heterostructure lasers. The lower temperature dependence of threshold current and smaller dynamic linewidth makes real index-guided InGaAsP MQW active layer lasers potentially attractive for many system applications.

Fabrication and performance characteristics of 1.55-μm InGaAsP multiquantum well ridge guide lasers

We report the fabrication and performance characteristics of InGaAsP ridge waveguide lasers with multiquantum well (MQW) active layers emitting near 1.55 μm. The active region has four active wells (1.55 μm InGaAsP) and three barriers (1.3 μm InGaAsP). The thicknesses of the active wells and the barrier layers are ∼250 Å. The 360-μm-long lasers have threshold currents in the range 60–80 mA at 30 °C, external differential quantum efficiency ∼25% at 30 °C, and T0∼70 K. The modulation bandwidths of the lasers are ∼1.5 GHz and they exhibit less frequency chirping than similar lasers with conventional double heterostructure (DH) active layer. Since frequency chirp limits the performance of high bit rate long haul fiber communication system at 1.55 μm, we believe MQW lasers offer an advantage over conventional DH lasers.

Ga0.47In0.53As/InP multiquantum well heterostructure lasers grown by molecular beam epitaxy operating at 1.53 μm

Current injection Ga0.47In0.53As/InP multiquantum well heterostructure lasers operating at 1.53 μm have been successfully prepared by molecular beam epitaxy. These lasers consist of four ∼70 Å Ga0.47In0.53As wells and three ∼150 Å InP barriers. The threshold current density is 2.7 kA/cm2. In the temperature range of 10–75 °C, the threshold-temperature dependence can be described closely by a single temperature dependence coefficient T0. The measured T0 is 45 K. No significant improvement in T0 is observed in these multiquantum well lasers over conventional double-heterostructure lasers operating also at 1.5 μm.

Gain and carrier lifetime measurements in AlGaAs multiquantum well lasers

We have measured the gain and the carrier lifetime at threshold in shallow proton stripe AlGaAs multiquantum well lasers with several different active layer structures. The lasers studied had active layers with two wells, four wells, six wells, and the modified multiquantum well. The net gain <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> is found to vary almost linearly with the injection current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</tex> for all the laser structures studied. The slope <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dG/dI</tex> is largest for the modified multiquantum well (MMQW) laser which is consistent with the observed lowest threshold current of these devices. We find that the carrier density at threshold for the MMQW laser is about a factor of 4 lower than that for a single quantum well laser. Thus, the effect of a nonradiative mechanism (e.g., Auger effect) which varies superlinearly with the injected carrier density is considerably reduced in MMQW lasers compared to that in single quantum well (SQW) lasers or the conventional double heterostructure lasers. The reduced threshold carrier density of the MMQW lasers has important implications for high temperature performance of lasers fabricated from the InGaAsP/InP material systems which are believed to have nonradiative mechanisms that vary superlinearly with carrier density, particularly for those laser structures for which the high temperature operation is not limited by leakage current.

Gain and carrier lifetime measurements in AlGaAs single quantum well lasers

We have measured the gain and the carrier lifetime at threshold in shallow proton stripe AlGaAs multiquantum well lasers with several different active layer structures. The lasers studied had active layers with two wells, four wells, six wells, and the modified multiquantum well. The net gain G is found to vary almost linearly with the injection current I for all the laser structures studied. The slope dG/dI is largest for the modified multiquantum well (MMQW) laser which is consistent with the observed lowest threshold current of these devices. We find that the carrier density at threshold for the MMQW laser is about a factor of 4 lower than that for a single quantum well laser. Thus, the effect of a nonradiative mechanism (e.g., Auger effect) which varies superlinearly with the injected carrier density is considerably reduced in MMQW lasers compared to that in single quantum well (SQW) lasers or the conventional double heterostructure lasers. The reduced threshold carrier density of the MMQW lasers has important implications for high temperature performance of lasers fabricated from the InGaAsP/InP material systems which are believed to have nonradiative mechanisms that vary superlinearly with carrier density, particularly for those laser structures for which the high temperature operation is not limited by leakage current.