InGaAsP Epilayers Research Articles

Characterization of surface deformation around Vickers indentations in InGaAsP epilayers on InP substrate

The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased.

InGaAsP/GaInP/AlGaInP 0.8 μm QW lasers grown by MOCVD using TBP and TBAs

InGaAsP epilayers and InGaAsP/GaInP single quantum well (SQW) structures have been grown by metalorganic chemical vapor deposition (MOCVD) on GaAs substrates using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBAs) as group V sources. Both InGaAsP epilayers and InGaAsP/GaInP SQW structure show strong photoluminescence emission, suggesting good optical quality. Finally, ridge waveguide InGaAsP/GaInP/AlGaInP QW lasers have been demonstrated with an emission wavelength around 0.8 μm and a threshold current of 24 mA under continuous wave operation at room temperature, indicating TBP and TBAs are as good as PH 3 and AsH 3 for the growth of high-power 0.8 μm lasers.

Optical studies of the Holmium-doped InGaAsP epilayers

Photoluminescence (PL), contactless electroreflectance (CER), and Raman scattering measurements have been used to study the structural properties of Ho-doped InGaAsP epilayers. Both the full width at half maximum (FWHM) of PL and the broadening parameter of CER are decreased as the doping amount of Ho element increases. This indicates that Ho doping greatly reduces the residual impurities and improve the quality of epilayers. The Raman spectra of Ho-doped InGaAsP epilayers are found to have asymmetric line shapes. Using a spatial correlation model, it is found the asymmetric broadening of the Raman signal is not influenced by the Ho doping. We hence conclude that the introduction of the Ho element can greatly reduce the residual impurities of LPE-grown layers, but no large amounts of Ho element are being incorporated into the epilayers during the purification. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical properties of Nd-doped InGaAsP epilayers

The optical properties of Nd-doped InGaAsP epilayers grown by liquid phase epitaxy (LPE) have been studied by photoluminescence and Raman scattering. The full width at half maximum (FWHM) of the photoluminescence peak has been found to decrease as the doping amount of Nd element increases. The narrowest value of the FWHM of PL peak is 7.5 meV, which is smaller by about 46% than that of the undoped InGaAsP and better than previous reports on similar composition layers. Using a spatial correlation model, we found that the asymmetric broadening of the lineshape of the Raman signal is not influenced by the Nd doping. We hence conclude that the introduction of the Nd element can greatly reduce the residual impurities of LPE-grown layers, but the Nd element is not incorporated into the epitaxial layers during the purification.

Persistent photoconductivity in Ho-doped InGaAsP epitaxial layers

Persistent photoconductivity (PPC) was investigated in Ho-doped InGaAsP epilayers with Ho concentrations in the range of 0–0.15 wt%. The decay behavior of PPC resembles that of Al x Ga 1− x As and can be well described by a stretch-exponential function. The temperature-dependent PPC studies show that the lattice relaxation of DX-like centers is responsible for the PPC effect. As the Ho doping increases, the decay-time constant and the electron-capture barrier were found to decrease. We suggest that the introduced Ho elements may chemically react with donor impurities, suppressing lattice relaxation and hence reducing the electron-capture barrier. Also, rare earth doping is demonstrated to be an effective method of improving the quality of InGaAsP epilayers.

Growth and Performance Study of Aluminum-Free InGaAs/GaAs/InGaAsP Strained Quantum-Well Pump Lasers

The growth of InGaP, InGaAs and InGaAsP epilayers lattice matched to GaAs using the low pressure organometallic vapor phase epitaxy (LP-OMVPE) system was investigated. For the application of erbium-doped fiber amplifiers (EDFAs), the emission wavelength and far-field pattern of the pump laser were designed. The optical and electrical performances of the resultant pump laser were measured.

X-ray diffraction analysis of a selectively grown InGaAsP epitaxial layer

We analyzed compositional fluctuation with lattice relaxation in a selectively grown InGaAsP epilayer by x-ray diffraction measurement. A simple and deterministic analysis procedure is described for analyzing the distribution of lattice constants (Δa⊥,Δa∥). The method is based on the systematic analysis of hkl-dependence of x-ray peak profiles. The method makes the direct observation of the distribution of lattice constants easier and is suitable for analysis of selectively grown samples. The method is applicable to a selectively grown InGaAsP epilayer with a small strain under a dislocation-free condition. Clear lattice relaxation is experimentally confirmed in the epilayer and is identified as the elastic relaxation that is caused by the three-dimensional shape of the selectively grown region. This is a direct observation of elastic relaxation in a selectively grown dislocation-free structure by x-ray diffraction measurement. Distributions of both perpendicular and parallel lattice constants are estimated from the x-ray data. The result shows that both the composition and relaxation rate fluctuate in the sample.

LPE growth and characterization of InGaAsP/InP heterostructures: IR light-emitting diodes at 1.66 μm. Application to the remote monitoring of methane gas

Highly effective IR light-emitting diodes operating at the wavelength 1.66 μm and based on the buried heterostructure In 0.88Ga 0.12As 0.26P 0.74/ In 0.72Ga 0.28As 0.62P 0.38/In 0.53Ga 0.47As/InP have been grown by liquid-phase epitaxy (LPE) and characterized in detail by means of transmission electron microscopy (TEM), high-resolution electron microscopy (HREM), electron diffraction (ED), X-ray diffraction (XRD), secondaryion mass spectrometry (SIMS) and electroluminescence measurements, The InGaAsP epilayers are found to be well lattice matched and of good structural quality. A tentative explanation is presented for the spinodal decomposition observed in InGaAsP alloys. A new type of selective CH4 gas sensor has been developed and fabricated on the basis of the IR light-emitting diode mentioned above. Especially designed for the remote control of CH 4 gas via fibre optics, an integrated optoelectronic readout scheme has been developed and tested. It is shown that the proposed type of sensor can be used for the quantitative remote control of CH 4 gas concentration (0.2-100%) via a fibre glass line up to a distance of 2 × 1 km.

Characterisation of the LPE grown InGaAsP/InP hetero-structures: IR-LED at 1.66 μm used for the remote monitoring of methane gas

Combined TEM, HREM, ED, SIMS, X-ray and electroluminescence studies were used to characterise in detail a highly effective IR-LED emitting at the wavelength 1.66 μm and based on buried heterostructure In0.88Ga0.12As0.26P0.74/In0.72Ga0.28As0.62P0.38/In0.53Ga0.47As/InP grown by liquid-phase epitaxy. The InGaAsP epilayers were found to be well lattice-matched, dislocation free and of good structural quality. A tentative explanation is presented for the spinodal decomposition observed in InGaAsP alloys. A new type of selective methane gas sensor has been developed and fabricated on the basis of the IR-light emitting diode mentioned above. It is shown that the proposed type of sensor can be used for the quantitative remote control of methane gas concentration (0.2–100%) via a fibre glass line up to the distance of 2 × 1 km.

Shear deformation potential of elastically strained InGaP/GaAs(111)B and InGaAsP/GaAs(111)B films

Elastically compressed InGaAsP epilayers were grown in a wide interval of compositions (with bandgaps from 1.4 to 1.9 eV) on GaAs(111)B substrates by liquid phase epitaxy. The splitting of the valence band was found by taking the derivative of photocurrent spectra. Its value was as high as meV for narrow-bandgap epilayers ( eV) and eV for wide-bandgap epilayers ( eV). The calculated shear deformation potential, d, was found to be eV for narrow-bandgap and eV for wide-bandgap films. A nonlinear dependence of the valence-band splitting on elastic strain was clearly observed for the wide-bandgap epilayers. This nonlinearity was explained by taking into account the interaction of the light-hole band with the spin - orbit-split valence band.

Influences of Interfacial Misfit Stress on Modulated Microstructures of InGaAsP / InP Heterostructures

The misfit stresses of metallorganic chemical vapor deposition grown heterostructure wafers were determined and their effects on the modulated microstructures of epilayer were investigated. Lattice mismatches were measured using {511}asymmetric and (400) symmetric x‐ray reflections. Elastic strains were obtained from the parallel mismatches and were used for determining the misfit stresses. Transmission electron microscopy results showed the presence of the modulated microstructures (spinodal decomposition) in the epilayer. It was found that the modulation periodicity varies with the lattice mismatches. To investigate this observation, the interaction elastic energy induced by misfit stress was derived and used to explain the experimental results. Good agreement was obtained between the measured and calculated modulation wavelength. Also, contributions from the composition and misfit stress to variation of modulation periodicity were separated out, and the misfit stress was found to have the larger contribution. Thus, it is concluded that the interfacial coherency and misfit stress have large influences on the microstructures of the InGaAsP epilayer, particularly on the modulation wavelength.

Electron microscopy and mass-spectrometry study of In0.72Ga0.28As0.62P0.38 lasers grown by liquid phase epitaxy

Broad area as well as buried heterostructure lasers based on In0.72Ga0.28As0.62P0.38/InP and emitting at 1.3 μm are grown by liquid phase epitaxy and are studied in detail by means of transmission electron microscopy, X-ray diffraction, secondary ion mass-spectrometry, and electroluminescence. The InGaAsP epilayer is found to be well lattice-matched and of good structural quality. A tentative explanation is presented for the spinodal decomposition observed in the InGaAsP alloy. We also report on the high performance characteristics of the infrared lasers.

Electron microscopy and mass-spectrometry study of InGaAsP/InP heterostructures (pin diodes) grown by liquid phase epitaxy

Large area InGaAsP/InP double heterostructures for λ = 1.3 and 1.55 μm applications grown by liquid phase epitaxy are studied in detail by means of transmission electron microscopy, high resolution electron microscopy, X-ray diffraction, secondary ion mass-spectrometry, and photoluminescence. The InGaAsP epilayers are found to be well lattice matched and of excellent structural quality. A qualitative explanation is provided for the spinodal decomposition observed in the InGaAsP alloy for λ = 1.3 μm. The high performance characteristics of the infrared photodiodes based on this double heterostructure are reported as well.

Implant-damage isolation of InP and InGaAsP

The creation of high resistivity layers by ion implantation of doped InP and InGaAsP epilayers, and the potential of the implant-isolation technique for the fabrication of InP-based ridge waveguide lasers, have been investigated. InP and InGaAsP samples, doped with 5×1017 cm−3 Si or Zn, were implanted with multiple-energy 4He or 16O. Ridge waveguide lasers, with ∼0.7 μm dielectric masks to protect the ridge, were implanted with 18O ions. In all cases, the implantation beam flux was maintained at 0.01 μA cm−2. Following 30 s rapid thermal annealing (RTA) in the temperature range 350–750 °C, the sheet resistivities of the InP and InGaAsP samples were determined using either a contactless eddy current or Hall effect measurements. The results show that in both InP and InGaAsP high resistivity layers (∼105 Ω/⧠) are produced by He or O implantation. The thermal stability of the implant-induced isolation depends on the material, the doping type, and the ion dose. High sheet resistivity, stable against 30 s RTA, can be maintained for temperatures up to 550 °C, sufficient for device processing. For samples implanted to calculated (trim) defect concentrations of ∼4×1021 cm−3, p- to n-type conductivity conversion was observed for both InP and InGaAsP.

Composition assessment by spatially resolved photoluminescence of InGaAs and InGaAsP epilayers grown on recessed InP substrates

Epitaxial layers of InGaAs and InGaAsP have been grown on InP recessed substrates by MOVPE. Spatially resolved photoluminescence (PL) at low temperatures has been used to assess the quality of material grown both in the bottom of the recess and on the sidewalls. PL signals from ternary and quaternary epilayers grown on a 100 mu m wide recess both show significant perturbations (10-20 meV) in PL energy at the sidewalls compared with the bulk value. In the middle of the InGaAs recess the lattice-matched PL energy is not re-established, with a blue shift indicating Ga-rich material. For the InGaAsP recess a smaller blue shift in PL energy from the middle of the recess is observed. The effect of growth parameters (reactor pressure and gas flow rate) and the influence of recess width on the perturbation to the PL energy and quality of the InGaAs epilayers described above has also been evaluated.

Zn-doped InGaAsP (1.3 μm) contact layer for an inverted DH laser structure

Zn as an acceptor in InGaAsP (1.3 μm) epilayers grown and doped by liquid-phase epitaxy was investigated for its dependence on growth parameters to establish optimum conditions for a bottom contact layer of a double-heterostructure (DH) laser diode monolithically integrated with its driver circuit on a semi-insulating InP substrate. Carrier concentrations, measured by the Van der Pauw technique and electrochemical C / V profiling (ECV), increase with the mole fraction of Zn added to the In melt until a maximum of about 1×10 19 cm -3 si reached. Nearly constant room temperature mobilities, which are larger than published data for Cd-doped InGaAsP, were obtained in a carrier concentration range of 1×10 18 to 1×10 19 cm -3. A minimum value of 1.3×10 -2 ω cm was achieved for the resistivity at room temperature. ECV profiling shows that, beyond the hole-concentration maximum, a further increase in the amount of Zn added to the growth solution leads to an enhanced outdiffusion of Zn into the InP substrate. Two diffusion fronts were observed, indicating that two different diffusion mechanisms take place. The crystal quality of the epitaxial layers was studied by photoluminescence microscopy and spatially resolved cathodoluminescence. Uniform luminescence images were obtained for the layers doped to the maximum hole concentration. Double crystal X-ray topography revealed extended regions where the lattice mismatch relative to the InP substrate is only of the order of 10 -7.

The In xGa 1− xAs yP 1− y (0.53< x

A systematic study in the growth of In x Ga 1- x As y P 1- y (0.53< x<1,0< y<1) compound semiconductor and its application to laser diode structure had been carried out by the low-pressure organometallic vapor phase epitaxy (LP-OMVPE) technique. The indium, gallium, arsenic and phosphorus incorporation efficiencies were studied. At the optimized growth conditions, the In incorporation efficiency has been found to be about 0.7 as compared with that of Ga in both In 0.53Ga 0.47As and InGaAsP epilayers. However, the P incorporation efficiency was found to be much lower than that of the As. Furthermore, we found that the As composition in In x Ga 1- x As y P 1- y quaternary epilayers (Q layers) is determined by the arsine (AsH 3) flow-rate and not by the AsH 3/PH 3 flow-rate ratio in the gas phase. The hydride flow-rates have been explained by the proposed As/P competition model and then formulated. According to this model, the AsH 3 flow-rate was found to be proportional to y 2.24259(1- y) -0.4889, while the PH 3 flow-rate was controlled by a varying incorporation efficiency, C p that is varying as [ y(1- y] -0.27138. For the dummy laser structures, the photoluminescence (PL) measurements show higher emission intensity of a GRIN/strained QW/GRIN heterostructure than that of a non-strained GRIN/QW/GRIN structure. Moreover, we demostrate a sawtooth MQW structure having strong PL intensity, but widened peak shpae toward the high energy side that can be used as an active layer of a tunable wavelength LD structure.

Preparation and characterization of in1?xGaxAsyP1?y epilayers by liquid-phase epitaxy

In1−xGaxAsyP1−y epilayers with three different solid compositions of ln0.73Ga0.27As0.60P1.40, In0.59Ga0.41As0.87P0.13 and ln0.53Ga0.47As were grown on (1 0 0) InP substrate at 623° C by the step cooling technique of liquid-phase epitaxy. From the optical transmission measurements, the corresponding wavelengths of the InGaAsP epilayers were 1.30, 1.55 and 1.69 μm, respectively, which are in good agreement with those obtained from the calculations using Vegard's law. The full widths at half maximum of the photoluminescent spectra at 14 K of these layers were as low as 18.6, 22.5 and 7.9meV, respectively. The electron mobility of the InGaAsP epilayers is a function of the solid composition with the ln0.53Ga0.47As epilayer having the highest electron mobility. The mobility and concentration of this layer are 8,873cm2V−1 sec−1, 9.7×1015cm−3 and 22,900 cm2V−1 sec−1, 8.5×1015cm−3 at 300 and 77 K, respectively. The compensation ratio is between 2 and 5.

Application of tie-line concept on the liquid phase epitaxial growth of GaInAsP on InP

As the variation of melt composition follows the tie-line relation, an epilayer with a given composition can be grown from the melts with different compositions at a fixed temperature. This was tested by the LPE experiments of InGaAsP epilayer growth. A set of epilayers, with wavelength 1.55±0.05 μm and lattice matched to InP (100) substrate ( Δa a<0.3% ) , were obtained in the melt with different compositions. The growth rate of epilayers varied in different melts. This was due to the degree of supersaturation changing as the melt composition varied along the tie line. The relationship between epilayer growth rate and supersaturation was mathematically derived and qualitatively agreed with the experimental results.

Low temperature LPE growth and photoluminescence of InGaAsP on GaAsP

InGaAsP epilayers were successively grown on a GaAS 0.61P 0.39 substrate at a low growth temperature of 689°C. The characteristic convex relation between X ℓ Ga and X ℓ As was observed. Although the epilayer surfaces were almost mirror-like, somewhat rough surfaces were observed in the epilayers with medium band gaps. The samples with rough surfaces also had wider FWHM's in the photoluminescence spectra. A carrier concentration spike at the substrate-epilayer interface disappeared by lowering the growth temperature from 789 to 689°C. Compositional variation was observed in the epilayers having higher As content, which was due to P atom depletion from the melt.