InGaAsP InP Research Articles

Computer simulation of high frequency modulation of laser diode radiation

Dynamic characteristics in the case of a large signal of partly gain-coupled multiple-quantum-well InGaAsP–InP distributed feedback (GC DFB) laser diodes have been investigated. Simple rate equations for carrier and photon densities were taken. A possibility to simulate the modulation characteristics of GC DFB lasers using these equations has been shown. Chirp and optical power pulses obtained by time-resolved frequency chirp measurements were compared with modelled ones.

Study on the effects of well number on temperature characteristics in 1.3-μm InGaAsP–InP quantum-well lasers

Effects of well number on temperature characteristics in 1.3-μm InGaAsP–InP multi-quantum-well lasers have been investigated. A smaller well number is suitable for lower threshold current and higher differential quantum efficiency at 25 °C, while larger well number produces better performances at 85 °C. Furthermore, lasers with a larger well number can achieve a less output power penalty at high temperature. For the first time, a theoretical model has been established to precisely explain the relationship between the characteristic temperature of threshold current and that of external differential efficiency.

Fabrication and complete characterization of polarization insensitive 1310 nm InGaAsP–InP quantum-well semiconductor optical amplifiers

Polarization insensitive 1310 nm InGaAsP–InP multi-quantum-well (MQW) semiconductor optical amplifiers (SOAs), with 7° tilted ridge waveguide and buried-window end facets, have been fabricated and fully characterized on chip and module level. SOAs chips with an optimized complex strained MQW active region exhibited less than 1 dB polarization dependence of amplified spontaneous power in the drive current range of 50–200 mA. The amplifier module, having a residual facet reflectivity of 2.8 × 10−5, achieved 25 dB fibre-to-fibre unsaturated gain, for both transverse electric and transverse magnetic polarization states, 11.2 dBm saturation output power, and 7.6 dB noise figure at 1310 nm. The polarization dependence of gain was less than 0.6 dB in the 3 dB gain bandwidth of 56 nm. Coupling efficiency played a significant role in the gain, saturation output power and noise figure of a SOA module. Spot-size-converter integrated SOAs with buried heterostructures are expected to exhibit further improved performances.

A theoretical comparison of the pressure dependence of the threshold current of phosphorus-, aluminium- and nitrogen-based 1.3 µm lasers

A comparative study of the three competing laser materials, InGaAsP–InP, AlGaInAs–InP and InGaAsN–GaAs, has been undertaken, for the first time, involving threshold characteristics with pressure. In our theoretical study we investigate the factors that influence the material gain performance, the threshold characteristics and the pressure dependence of each of the laser systems. We find that AlGaInAs and InGaAsN active layer materials have substantially better material gain performance than the commonly used InGaAsP at room temperature. Both radiative and non-radiative current contributions for laser systems are compared using basic equations, which makes our analysis particularly attractive owing to its simplicity and ability to predict the main effects involved. We have found that the estimated variation of phonon-assisted Auger rates with pressure in the N-based system has a slower decrease than that of the other two laser systems. The threshold carrier density nth in the N-based system increases with pressure whereas it decreases in Al- and P-based laser systems. This opposite variation changes the overall behaviour of the threshold current in these three competing laser systems. Our theoretical calculations indicate a significant increase of the radiative to non-radiative recombination current in the N-based laser system. This result highlights the intrinsic superiority of the N-based laser system.

Improved performance of 1.3 µm InGaAsP–InP lasers with an AlInAs electron stopper layer

We have fabricated 1.3 µm InGaAsP–InP strained-layer multi-quantum-well (MQW) lasers with an AlInAs electron stopper layer (ESL). The ESL was inserted between the MQW active layer and the p-side separate confinement heterostructure (SCH) layer to suppress electron leakage in the conduction band from the active region to the p-cladding layer. Lasers with an ESL exhibited much improved temperature characteristics of threshold current and external slope efficiency. As a result, a lower power penalty of 2.2 dB from 25 °C to 85 °C was achieved at an injected current of 60 mA. The insertion of an AlInAs ESL into the SCH layer is a successful way to realize the uncooled operation of 1.3 µm InGaAsP–InP lasers at high temperatures.

Influence of intrinsic strain on the surface acoustic wave-induced birefringence in InGaAs–GaAs and InGaAsP–InP multiple-quantum-well optical modulators

The effect of intrinsic strain on the surface acoustic wave (SAW)-induced birefringence in InGaAs–GaAs and InGaAsP–InP multiple-quantum-well (MQW) optical modulators is investigated. We solve the exciton equation in momentum space using a two-dimensional quadrature method to obtain the birefringence Δn by the SAW induced strain. Our calculations are in good agreement with the experimental results in AlGaAs–GaAs and InGaAs–GaAs MQWs. Intrinsic strain influences the band mixing of valance subbands in quantum wells in the presence of asymmetric strain. We have shown that birefringence (Δn∼0.06) is significantly higher in tensile strained (ε∼0.7%) InGaAsP–InP MQWs than in compressively strained In0.21Ga0.79As–GaAs MQW devices.

Wide-range-tunable laterally coupled distributed feedback lasers based on InGaAsP–InP

We have investigated tunable distributed feedback (DFB) lasers based on InGaAsP quantum wells grown by molecular-beam epitaxy. Two-section tunable DFB lasers were fabricated by patterning laterally gain coupling binary superimposed gratings perpendicular to the ridge waveguide. Side mode suppression ratios of up to 42 dB have been achieved. The tuning range covers 25 nm.

Modeling of InGaAsP–InP 1.55 μm lasers with integrated mode expanders using fiber-matched leaky waveguides

A new concept for InGaAsP–InP 1.55 μm lasers integrated with spot size converters using leaky waveguides is presented. The large fundamental mode size and the high discrimination of the higher order modes make ARROWs (Antiresonant Reflecting Optical Waveguides) and antiguided waveguides useful for fiber coupling functions. Three-dimensional (3-D) beam propagation method (BPM) results show that the devices have transformation losses lower than 0.22 dB. Fiber-coupling efficiencies of 60% are possible with standard cleaved single-mode fibers (SMF). The horizontal and vertical FWHM can be efficiently reduced to 9.70° (horizontal) and 17.80° (vertical). The fabrication of such devices avoids the growth of thick layers of quaternary material with a low Ga and As fraction, and simplifies the fabrication to one planar epitaxial growth step and one non-critical conventional etch.

An in-depth analysis of reflections in MMI couplers using optical low-coherence reflectometry: design optimization and performance evaluation

This paper describes a comprehensive report on the high potential of optical low-coherence reflectometry (OLCR) measurements to assist the design optimization and performance evaluation of symmetric MMI couplers. Using three sets of deep-ridge InGaAsP–InP couplers on InP and by performing OLCR measurements simultaneously in reflection and transmission modes, the nature and origin of all reflections in MMI have first been identified with respect to a deliberately chosen design parameter, namely, the coupler length. In addition, and in total agreement with the self-imaging principle and also the BPM simulations, the back reflections in combiner mode are shown to be prominent even in fully optimized devices. Finally, a simple design artifact has been proposed and demonstrated experimentally for the first time to suppress back reflections.

Effects of irradiation on GaAlAs — GaAs and InGaAsP–InP lasers

An investigation was made of the radiation strength of GaAlAs—GaAs and InGaAsP—InP semiconductor lasers. This strength fell with increase in the laser emission wavelength. The highest radiation strength was observed for semiconductor lasers emitting at the wavelength of 0.85 μm.

Nature and origin of pure edge dislocations in low mismatched epitaxial structures

A study of pure edge misfit dislocations (L-MDs) in SiGe Si , Ge GaAs , GaAlAsP GaAs , GaAlAsSb GaSb and InGaAsP InP epitaxial structures grown by different techniques has been performed. A model for the formation of L-MDs from the parallel 60°-MDs pre-existing at the interface is proposed. The common dislocation node for these initial 60°-MDs, arising as a result of the dislocation reactions in crossing points of the MDs, is a starting point for L-MD generation. Initial MDs with appropriate Burgers vectors may be located at the interface at a distance of up to 0.5 μm apart. The process of L-MD propagation is accompanied by a shift of dislocations from the interface upwards into the epilayer or downwards into the substrate. The behavior of L-MDs is discussed in terms of dislocation mobility in the epitaxial layer at the growth temperature in heterostructures.

Influence of external optical feedback on polarization switching in [formula omitted] lasers

Optical feedback effects on the emission properties of 1.3 μm InGaAsP InP ridge waveguide lasers were studied experimentally for both dc pumping and current modulation. The laser diodes used in our experiments showed a current-induced transition from TM to TE polarization without external feedback. At external optical feedback, the current for the onset of TM/TE transition droped by 25 mA and multiple TM/TE switching was observed over a large current interval. The dynamic response of the external-cavity laser to current pulses of various width was found to depend sensitively on the fine tuning of the external cavity length, resulting in TM/TE oscillations of 2 or 10 GHz, respectively, in the case of 2 ns current pulses. The physical mechanism responsible for the observed behaviour is discussed.

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.

A three-terminal N-channel InGaAsP–InP-based double heterostructure optoelectronic switch (DOES)

In this work, we give the first report on the physical and functional characteristics of a three-terminal InGaAsP–InP-based double heterostructure optoelectronic switch (DOES) device. In this device, electrical contact is made to the emitter, collector, and active layers while optical input is made via a window in the emitter contact. The DC current–voltage characteristic of a 100 μm × 80 μm device exhibits a switching voltage of 6.6 V with an OFF-state resistance of 200 kΩ and an ON-state resistance of <50 Ω. In conjunction with the electrical outputs, optical emission is generated with a ratio of >10 in the light emission between the ON (2 mA) and OFF states. We show that injection of current and (or) injection of light into the active region reduces the switching voltage. This is used to switch the device from the OFF state to the ON state without having to alter the output circuit bias (emitter–collector bias). The ability to switch the three-terminal InGaAsP–InP DOES with both electrical and optical inputs demonstrate its functionality, flexibility, and suitability for use in optoelectronic switching applications and for InP-based optoelectronic integrated circuits.

Growth of AlPSb and GaPSb on InP by gas-source molecular beam epitaxy

We have studied the growth conditions of AlPSb and GaPSb lattice match to InP substrates using gas-source molecular beam epitaxy. Mirror-like surface morphology was obtained under the lattice matching growth conditions. It was found that the solid compositions of AlPSb and GaPSb were sensitive to the relative flux ratio of the two group V elements (P,Sb) and to the growth temperature, respectively. The electrical properties of Be-doped and Si-doped GaPSb were characterized by Hall measurements at room temperature. In Si-doped GaPSb, electron concentration seems to saturate at 5 × 10 17cm −3. For optical properties, the ellipsometically measured refractive indices at 1.55 μm were 3.037 for AlPSb and 3.579 for GaPSb showed larger refractive index difference than the InGaAsP (E g = 1.45 μ m) InP system. 20 paris of AlPSb GaPSb DBR reflectivity measurements demonstrate a stop-band width of 206 nm with the maximum reflectivity exceeding 99%. This result will promise to be useful for long-wavelength surface emitting lasers.

Polarization-mode dynamics in strained 1.3 μm [formula omitted] lasers under picosecond current modulation

The dynamic behaviour of the TE and TM polarized output from ridge-waveguide InGaAsP InP lasers which are electrically pumped with 300 ps pulses is studied experimentally and theoretically. For the first time, different polarization characteristics depending on the amplitude of the current pulse and the level of the dc bias are reported. While strong mode competition resulting in TE or TM mode emission in separate current intervals is found in the cw regime, simultaneous lasing of both modes, transients between TE and TM in the ps range as well as common GHz relaxation oscillations of TE and TM emission are observed under pulsed excitation. TE and TM pulses shorter than 40 ps are measured. The laser dynamics is modelled through space-dependent rate equations. Numerical results suggest, that the fast polarization switching is due to a lateral shift of the TE and TM modes against each other.

Nanoscale structures in III–V semiconductors using sidewall masking and high ion density dry etching

A simple deposition and etch-back technique to form narrow (∼300 Å) masks for subsequent pattern transfer into semiconductors is reported. High ion density (∼5×1011 cm−3) electron cyclotron resonance CH4/H2/Ar (for In-containing materials) or BCl3/Ar (for Ga-containing materials) discharges are used to give anisotropic low-damage etching. After initial resist patterning using conventional stepper lithography, conformal plasma-enhanced chemical vapor deposition or reactive sputtering of a metal (W, WSix) or a low temperature dielectric (SiNx, SiO2) is followed by an anisotropic etchback to leave a thin sidewall on the resist feature. The resist is then removed by dry etching, leaving a sidewall which can be used as a mask for pattern transfer into the semiconductor. Examples of novel quantum-wire laser structures fabricated in GaN and InP–InGaAsP systems are given. The nanolaser structures can be integrated with microdisk lasers using combined dry etching and selective wet chemical etching. Low ion energies (<100 eV) are required to avoid sputtering of the mask material and changes in the near-surface stoichiometry of the semiconductor.

Growth and Characterization of In0.83Ga0.17As0.39P0.61 Layers by Liquid-Phase Epitaxy Using Erbium Gettering

The Er-doped InGaAsP epitaxial layers with a wavelength of 1.1 µm lattice-matched to InP have been grown by liquid-phase epitaxy. When the Er amount doped in the InGaAsP growth solution is lower than 0.21 wt%, it usually has a fairly shiny, smooth surface morphology and a flat interface between epitaxial layer and substrate. By the wavelength-dispersive-X-ray-spectrometry analysis, we find the Ga solid composition maintains the same as that in the undoped layer, while the As solid composition decreases linearly with increasing Er wt%. The lattice mismatch between InGaAsP layer and InP substrate also decreases linearly with the Er wt% in the growth solution. It may be due to the formation of microparticles of Er-rich compounds ErAs. All the Er-doped samples still exhibit n-type conduction, but its electron concentration decreases with increasing Er wt% and is one to two orders of magnitude lower than those of undoped layers. By the photoluminescence (PL) measurements at various temperatures and excitation levels from the undoped InGaAsP layers, we identify the three peaks associated with the near-band-to-band, shallow- and deep-donor-to-acceptor-pair transitions. However, the deep- and shallow-donor-to-acceptor recombination peaks will sequentially disappear with increasing Er wt% for the Er-doped layers. As the Er amount is above 0.54 wt%, only the near-band-to-band peak dominates the PL spectra and exhibit a full width at half maximum of 9.3 meV. These results can be attributed to the donor gettering in the presence of Er. In addition, the PL peak wavelength decreases linearly with increasing Er wt% due to the variations of solid composition and lattice mismatch in the Er-doped quaternary layers.

Atomic scale survey of III–V epitaxial interfaces

A novel scanning tunneling microscopy technique is reported, which displays the atomically resolved lattice sites on ultrahigh vacuum cleaved (110) cross sections of epitaxially grown semiconductor multilayers. Voltage selective imaging is used to display either the group III (empty state) sites or the group V (filled state) sites on GaAs–AlGaAs and InP–InGaAsP heterojunctions grown by molecular-beam epitaxy and metalorganic vapor phase epitaxy. The interfaces can be defined to an accuracy of ±1 unit cell. Charge density maps of the group III (Al–Ga) sublattice in AlGaAs and of the group V (As–P) sublattice in InGaAsP are generated for the first time, and these reflect the composition fluctuations on the atomic scale. A tentative assignment is given to the individual Al and Ga sites and the ‘‘roughness’’ of such interfaces on the atomic scale is discussed.

Erbium doping in InGaAsP grown by liquid-phase epitaxy

The Er-doped InGaAsP epitaxial layers lattice-matched to InP with wavelengths of 1.29 and 1.55 μm have been grown by liquid-phase epitaxy. When the Er amount doped in the InGaAsP growth solution is above 0.32 wt %, it will have a fairly rough surface morphology with many extensive deposits of erbium hydride and oxide. The lattice mismatch normal to the wafer surface between InGaAsP layer and InP substrate decreases linearly with the Er weight percent in the grown solution. From the wavelength-dispersive-x-ray-spectrometer analysis, we find the solid composition of the In1−xGaxAsyP1−y layer has been changed and may be due to the formation of microparticles of Er compounds, such as ErAs or ErP. This inference is also supported by photoluminescence (PL) measurements which show that the PL peak wavelength decreases with increasing Er wt %. The full width at half maximum of PL peak associated with the near band-gap transition has been effectively reduced and exhibits the narrowest value of 9.1 and 6.3 meV for the 1.29- and 1.55-μm-wavelength InGaAsP layers in the presence of Er. In addition, the carrier concentration of Er-doped InGaAsP layers are around 3–30×1014 cm−3 and is one to two orders of magnitude lower than those of undoped layers. These results can be attributed to the donor gettering by the rare-earth element of Er. The Er-related luminescence lines locate between 1.503 and 1.528 μm which differ from those previously reported at ∼1.54 μm and can only be observed for the 1.29-μm but not for the 1.55-μm-wavelength InGaAsP layers.