InGaAsP Active Layer Research Articles

Comparative modeling results for ridge waveguide MQW and hybrid Si/III-V lasers

In this study, 1550 nm ridge waveguide multi quantum well (MQW) and hybrid Si/III-V lasers are simulated and the results are studied in a comparative setting. InGaAsP active layers with a ridge waveguide length of 500 μm and width of 5 μm with six quantum wells are chosen for both MQW and hybrid Si/III-V lasers. The hybrid Si/III-V laser structure is obtained by integration of a ridge waveguide MQW semiconductor laser with a silicon-on-insulator (SOI) chip. The proposed structure allows laser mode to experience maximal gain available in the III-V region while maintaining a high coupling efficiency to Si-waveguide. The results demonstrate that the optical power generated by MQW active layer can be transferred to the silicon waveguide of the hybrid Si/III-V laser. In addition, an increase in the threshold current and degeneration in the frequency response of the hybrid laser are observed compared to the MQW one. The results also indicate that there is not a big difference between the ridge waveguide MQW and the hybrid Si/III-V lasers in terms of spectrum and spontaneous emission characteristics.

Strained InGaAsP multi-quantum-well structures for InP-based wide linewidth and polarization-insensitive semiconductor optical amplifiers

We have calculated the band structure of 1.55μm InGaAsP/InGaAsP multi-quantum-well structures using Lüttinger–Kohn Hamiltonian taking into account the strain in the quantum wells (QWs) and barriers, and the confinement in the quantum wells. Using the calculated dispersion curves and oscillator strength between the different interband transitions, we have determined the optical gain in TE and TM mode and the spontaneous amplified emission as a function of injected carrier density in devices composed of quantum wells with different thicknesses. We find that an optical gain linewidth larger than 130nm with a TE/TM polarization dependence lower than 1dB can be obtained using a three-quantum-well In0.53Ga0.47As0.96P0.04/InGaAsP active layer with quantum well thicknesses of 10, 14 and 19nm.

Polarization-Insensitive Monolithic 40-Gbps SOA–MZI Wavelength Converter With Narrow Active Waveguides

A polarization-insensitive monolithic 40-Gbps semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer wavelength converter has been developed. Based on the photon-electron rate equation, we optimized the dimensions of the waveguide structure to maximize the field confinement in the active layer. An InGaAsP active layer with narrow SOA waveguide effectively enables polarization-insensitive high-speed wavelength conversion. High-precision wafer processing technique enabled the fabrication of submicrometer-wide active waveguides with low current leakage. Input waveguide arrays were fabricated at intervals of 25 mum and mounted in a module with two-lens aspherical lens optics. The 40-Gbps nonreturn-to-zero wavelength conversion experiment demonstrates a clear eye opening over full C-band operation

GaAs/GaSb–AlAs/AlSb optical Bragg reflectors

Semiconductor Bragg mirrors on InP substrates that use GaAs/GaSb and AlAs/AlSb superlattices for the optically reflecting layers are described. The use of superlattices circumvents difficulties with growth of the GaAsSb and AlAsSb alloys, and they are transparent for wavelengths as short as 1050 nm. The mirrors can be combined with conventional InGaAsP active layers that can also be grown on InP.

Two-dimensional photonic crystal hexagonal waveguide ring laser

Hexagonal ring-type resonators defined by two-dimensional photonic crystal waveguides are proposed and demonstrated. Lasing actions are observed from the photonic crystal ring resonator patterned on a free-standing slab with InGaAsP active layers emitting near 1.55 μm. For a ring resonator with 8-μm diameter, the threshold peak pump power is ∼3 mW. The quality factor of the ring resonator mode estimated from below-threshold linewidth shows that the sum of the propagation loss and the bending loss of the photonic crystal ring resonator is less than ∼260 cm−1. The photonic crystal ring resonators can be used for the characterization of the optical losses in photonic crystal waveguides.

Gain/loss characterisation of optical waveguide and semiconductor laser structures

Finite element analysis, employing the H-field vector and scalar formulations, has been used with the aid of perturbation techniques to determine the modal gain and loss characteristics of optical waveguides and semiconductor laser structures. The accuracy and the applicability limits of the perturbation method are examined, and compared to the more accurate but more computer intensive transverse magnetic field formulation for an embedded-channel waveguide. Further, the method is applied to a rib-waveguide laser structure, where the imaginary part of the refractive index of the InGaAsP active layer is seen to vary according to the carrier concentration profile. Finally, the accuracy of a widely used but simpler method for determining the modal gain for QW and MQW laser structures, in terms of the optical mode confinement, is determined.

Nonlinear optical and bistable properties of a wafer-fused vertical-cavity device based on InGaAsP

We report on a detailed analysis of the nonlinear characteristics at 1.55 μm wavelength of a bistable device realised by wafer fusion of an InGaAsP InP heterostructure on an AlAs GaAs Bragg mirror. A sub-milliwatt threshold power and a switching contrast up to 70 : 1 have been obtained. The bistable behaviour has been observed over more than a 2.5 nm range. The carrier-induced dispersive nonlinearity of the InGaAsP active layer has been investigated, including the saturation behaviour of the nonlinear index change. A saturating value δn s = −3.1 × 10 −2 has been obtained at the wavelength corresponding to a linear absorption of 134 cm −1. The nonlinear refractive index cross-section is found in good agreement with a two-band absorption saturation model. Similarly, the switching thresholds are well described by a simple plane-wave model including nonlinear index saturation.

Catastrophic degradation lines at the facet of InGaAsP/InP lasers investigated by transmission electron microscopy

Material transformations occurring at the facets of optically ‘‘stressed’’ planar InGaAsP/InP diode lasers have been investigated by transmission electron microscopy and energy dispersive x-ray spectroscopy. Catastrophic degradation lines (CDLs) which are characteristic of catastrophic optical damage are observed for optical power densities ∼107 W/cm2. Analysis of the microstructure reveals a series of 150 nm wide GaAs-rich tracks and the formation of unique void/InGa-rich precipitate pairs within the InGaAsP active layer. These observations suggest that the formation of local group III-rich regions is the first stage in the formation of CDLs. Subsequently, the strong absorption of the impinging laser beam leads to propagation of an InGa-rich melt, thereby producing the GaAs-rich tracks through a process similar to liquid phase epitaxy. These results are discussed in the context of standard physical models for CDLs.

Very low power consumption semiconductor optical amplifier array

Very low power consuming and polarization insensitive semiconductor optical amplifier arrays with submicron-wide InGaAsP active layers are realized by selective MOVPE technique. 20-dB signal gain at a low injection current of 25 mA was achieved in four-channel arrays. >

The effects of strain on the threshold current density in InGaAsP/InP strained-layer single-quantum-well lasers

Basic design principles are formulated for minimizing the threshold current density in InGaAsP/InP strained-layer single-quantum-well (SL-SQW) lasers. A quaternary InGaAsP active layer is shown to provide more freedom in design than a ternary InGaAs active layer because the amount of strain (both tension and compression) and quantum-well thickness can be independently determined in the InGaAsP system for a given emission wavelength. Strain-induced changes in the valence-band structures are analyzed within the framework of k⋅p theory by taking into account the interaction with spin-orbit split-off bands as well as heavy-hole and light-hole bands. It is clarified that the quantum-well thickness plays a more significant role than the amount of strain when designing compressive-strained wells, while the situation is just the opposite in tensile-strained wells. It is shown that, although the application of biaxial tension reduces the threshold current density in bulk-like SL-SQW lasers more significantly than biaxial compression, the quantum-confinement effect has a pronounced impact on the reduction in the current density in compressive-strained wells. This makes either type of strain attractive for reducing the threshold current density in InP-based SL-SQW lasers.

Optical properties of semiconductor lasers with hydrostatic pressure

The pressure dependence of the stimulated emission of a 1.3 μm In1−xGaxAsyP1−y (y=0.6) buried heterostructure laser has been measured up to 2.5 GPa. In this pressure range the laser output was tuned over 200 nm. The laser output energy varied linearly with pressure at a rate of (80±3) meV/GPa, corresponding to variation of the direct band gap of the InGaAsP active layer with pressure. From the measured energy shift and from calculations of the fractional volume change in the active layer for the strain conditions of the epilayer, a hydrostatic deformation potential of (−5.7±0.1) eV was obtained.

Calculating the optical properties of multidimensional heterostructures: Application to the modeling of quaternary quantum well lasers

A method for calculating the electronic states and optical properties of multidimensional semiconductor quantum structures is described. The method is applicable to heterostructures with confinement in any number of dimensions: e.g. bulk, quantum wells, quantum wires and quantum dots. It is applied here to model bulk and multiquantum well (MQW) InGaAsP active layer quaternary lasers. The band parameters of the quaternary system required for the modeling are interpolated from the available literature. We compare bulk versus MQW performance, the effects of compressive and tensile strain, room temperature versus high temperature operation and 1.3 versus 1.55 pm wavelength operation. Our model shows that: compressive strain improves MQW laser performance. MQW lasers have higher amplification per carrier and higher differential gain than bulk lasers, however, MQW performance is far from ideal because of occupation of non-lasing minibands. This results in higher carrier densities at threshold than in bulk lasers, and may nullify the advantage of MQW lasers over bulk devices for high temperature operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multifunctional photonic switching operation of 1500 nm Y-coupled cavity laser (YCCL) with 28 nm tuning capability

The authors present new results on extended electrical tuning, fast spatial switching, and optically controlled wavelength conversion characteristics for the recently developed InP-based Y-laser structure. The devices have a 80 nm thick bulk InGaAsP active layer and are completely grown by metalorganic vapor phase epitaxy. The facets at both ends of the chip are as-cleaved without antireflective coating. The addressable range for electrically controlled wavelength switching was extended to the record value of 28 nm. When operated as a lossless 1:2 optical space switch, fiber-to-fiber gain >0 dB, extinction ratio >50 dB and high speed operation up to 1 Gb/s were shown. Optically triggered tunable wavelength conversion including dynamic operation was also demonstrated. >

The effect of interstital Frank partial dislocations on the gradual degradation of 1.3-μm double-channel planar buried heterostructure laser diodes

The structure of defects occurring in degraded 1.3-μm double-channel planar buried heterostructure type laser diodes was studied in detail by conventional diffraction contrast, weak-beam dark-field microscopy and high-resolution lattice imaging in a transmission electron microscope. The electrical activity of the defects was analyzed by means of the electron-beam-induced current. Device degradation is associated with the presence of interstitial Frank partial dislocation loops with a Burgers vector of (a/3) {111} at the interfaces between the InGaAsP active layer exposed after the channel etching and the first p+-InP layer of the liquid-phase-epitaxy-grown current-blocking layers. No other types of defects were observed in the course of the present study. The implications of the latter finding are far-reaching and lead to a new degradation model for the microstrctural changes associated with the gradual degradation of long-wavelength lasers. A new degradation model is proposed, and laser diode design considerations for degradation-free operation are given. These consdierations are twofold: the device structure should (a) not favor Frank partial dislocation loop nucleation and (b) suppress the dissociation of the Frank partial dislocations.

Localization of degradation in InP/InGaAsP mushroom stripe lasers

The rapid degradation observed in InP/InGaAsP mushroom stripe lasers covered with phosphosilicate glass (PSG) was investigated by comparing the light-current characteristics as a function of the preparation technique. We were able to show that the PSG-covering layer is not the reason for the rapid degradation. By inspecting the light-current characteristics before and after degradation and by additional underetching the laser structure after degradation we were able to localize the degraded regions on the open side walls of the InGaAsP active layer.

Elastic Stresses in InGaAsP Heterostructures with Alloyed Contact Metallizations

ABSTRACTWe have measured the radius of curvature of InGaAsP/InP heterostruc-ture wafers grown by liquid phase epitaxy, after growth and after broad area p-and n-metallizations used in the fabrication of 1.3vm lasers, by the x-ray automatic Bragg angle control technique. The heterostructure consisted of an n-InP buffer layer (0.2μm), an InGaAsP active layer (0.3 – 0.4μm), a p-InP layer (0.7μm) and either a p-InGaAsP or a p-InGaAs cap layer (0.6 – 0.7μm) grown on a 250 μm thick n-Inp substrate. The radius of curvature measured after growth was found to be in good agreement with the value calculated using the lattice mismatch strains. The changes in the radius of curvature after deposition and alloying of a 1000 Å thick AuZnAu p-metallization and after thinning the substrate to 86μu followed by 2900 Å thick alloyed GeAu n-metallization are such that the metal films are under a tensile strain. The value of the strain is calculated to be 8 × 10-3 and 1.6 × 10-3 respectively for the p- and n-metals. The radius of curvature was measured after the final metallization and annealing of 2500 A thick TiPt layer on the p-side. The annealed TiPt layer was found to have a compressive strain of 6 × 10-3. The stress in the active layer remained tensile at all times for both wafers and it was in the range 9 × 10 – 1.4 × 10 dyne cm-2. These values are less than the estimated fracture stress of InGaAsP by an order of magnitude.

Photoluminescence investigation in N type InGaAsP heterostructure

Photoluminescence of NInGaAsP multiepilayers has been observed. The wafers used have the structure of NInGaAsP active layer (Eg∼0.95eV) /NInGaAsP confinement layer (Eg∼1.2eV) /NInP substrate. Several radiation emission peaks can be seen in the photoluminescence spectra, which are identified as band to band recombination and recombination between electrons in the conduction band and holes in the split-off valence band in both the active layer and the confinement layer respectively. The fact that all layers used are N-type material excludes any uncertainties resulting from electron leakage and provides new evidence that hole leakage occurs in present structures and is enhanced by the split-off valence band.

Temperature-dependent polarization behavior of semiconductor lasers

InGaAsP lasers are found to operate in a pure TM mode or in a mixture of TE and TM modes at low temperatures. The polarization change at low temperatures is attributed to a thermal-stress effect in the InGaAsP active layer. However, none of the AlGaAs/GaAs lasers tested exhibits such behavior because the thermal stress in the active layer is significantly offset by the GaAs substrate.

Spatially resolved observation of carrier leakage in 1.3-μm In1−xGaxAsyP1−y lasers

We report spatially resolved observation of carrier leakage over heterobarriers between a thin InGaAsP active layer (eg∼0.9 eV) and symmetric InGaAsP confining layers (Eg∼1.28 eV), in a double-heterostructure laser. Peaks of short wavelength emission of about 1 μm were found to originate from the confining layers indicating that significant carrier leakage, not only of electrons but also of holes can occur. Additional experimental observations suggest that the surprising observation of significant hole leakage may be due to the existence of hot holes created by Auger and/or intervalence band absorption processes.

Minority carrier lifetime and luminescence efficiency of 1.3 µm InGaAsP-InP double heterostructure layers

Minority carrier lifetimes and quantum efficiencies were measured for a series of 1.3 μm InGaAsP active layers. Radiative and nonradiative components of lifetime as a function of electron and hole density were determined from this data. The measured lifetimes were T \approx 26 (1018cm-3/p)1.2ns for p-type, and T \approx 33 (1018cm-3/n)0.8ns for n-type material. The drop in efficiency with doping is consistent with the ratio of nonradiative and radiative rates being proportional to carrier density. The nonradiative and radiative rates are equal at p = (2.5 \pm 0.9)10^{18} cm-3and n = (3.3 \pm 0.7)10^{18} cm-3. A lifetime of 200 ns was observed for an undoped sample with a 0.2 μm thick active layer. The long lifetime shows that recombination with background traps is quite small, and that the interface recombination velocity is less than 50 cm/s, an order of magnitude less than for AlGaAs-GaAs double heterostructures. The minority carrier lifetime increases with temperature in lightly doped samples, as expected for radiative recombination, and shows little change with temperature in heavily doped samples. If the measured nonradiative rate is assumed to be due to the free carriers and not due to doping related traps, it can nearly account for the temperature dependence of laser threshold currents and for light-emitting diode efficiency.