InGaAs QWs Research Articles

Lifetime behavior of laser diodes with highly strained InGaAs QWs and emission wavelength between 1120 nm and 1180 nm

Highly strained InxGa1−xAs QWs are commonly used for laser diodes in the wavelength range beyond 1100 nm, but they suffer from strain induced formation of defects. The effect of different laser structures and different laser layouts on the aging behavior was investigated. If grown and processed under optimized conditions, laser diodes emitting at 1120 nm, 1156 nm and 1180 nm have lifetimes of several 1000 h up to more than 20,000 h in dependence on structure or indium content.Laser diodes with three different emission wavelength were mounted in a microoptical bench with a second harmonic generation crystal. From these benches laser emission in the green-yellow spectral range with more than 800 mW output power was obtained.

Comparative study on stained InGaAs quantum wells for high-speed optical-interconnect VCSELs

The gain-carrier characteristics of InGaAs quantum well for 980 nm high-speed, energy-efficient vertical-cavity surface-emitting lasers are investigated. We specially studied the potentially InGaAs quantum well designs can be used for the active region of energy-efficient, temperature-stable 980-nm VCSEL, which introduced a quantum well gain peak wavelength-to-cavity resonance wavelength offset to improve the dynamic performance at high operation temperature. Several candidate quantum wells are being compared in theory and measurement. We found that ∼5 nm InGaAs QW with ∼6 nm barrier thickness is suitable for the active region of high-speed optical interconnect 980 nm VCSELs, and no significant improvement in the 20% range of In content of InGaAs QWs. The results are useful for next generation green photonic device design.

Growth of laser diode structures with emission wavelength beyond 1100 nm for yellow–green emission by frequency conversion

Laser structures for emission wavelengths of 1120nm and 1180nm, suitable for non-linear frequency conversion to yellow–green and yellow–orange, were developed. At 1120nm emission wavelength different active regions and structures were investigated. The introduction of a GaAs spacer layer between GaAsP barriers and InGaAs QWs reduces threshold and transparency current density significantly. Lifetime measurements were done successfully over 1700h for broad area and 10000h for ridge waveguide tapered lasers.Broad area laser diodes with a partly strain-compensated 6nm InGaAs QW, emitting at 1180nm, show lifetimes above 1000h at an output power of 1.5W. The required beam quality was achieved by processing a ridge waveguide laser with an included distributed Bragg reflector. Such a laser emits up to 200mW in single mode output power.

Strong coupling between Tamm plasmon and QW exciton

We report on the strong coupling between a Tamm plasmon mode and excitons from inorganic quantum wells. The sample is formed by an AlAs/GaAlAs Bragg reflector containing InGaAs QWs in its high refractive index layers, on top of which a thin silver film is deposited. Angle resolved reflectometry experiments at low temperature (77 K) show a clear anticrossing in the dispersion relations, evidencing the strong coupling regime. The Rabi splitting amounts to 11.5 meV. Emission from low and high energy Tamm plasmon/exciton polaritons is also demonstrated. Experimental data are in very good agreement with transfer matrix simulations.

GaAs Based InAs/InGaAs Quantum Dots-in-a-Well Solar Cells and Their Concentration Applications

AbstractQuantum dot (QD) solar cells have been actively investigated recently since they have been theoretically shown to have the potential to realize high conversion efficiencies. However, very little research has analyzed the effect the dots have on the transport or recombination effects in the device. In this paper, we report the I-V and spectral response characteristics of InAs/InGaAs “dots-in-a-well” (DWELL) solar cells and compared them with GaAs control cells. The QD cells show higher short circuit density (Jsc) and better long-wavelength efficiency compared to the control cell. By comparing the dark current behavior of the QD cells to the GaAs control cells, we have conservatively estimated the concentration level at which the QD solar cells would surpass GaAs control devices.The quantum dot solar cells are grown by molecular beam epitaxy using the DWELL technique and a standard pin structure. The control cell structure is similar to the QD one except that there are no InAs dots or surrounding InGaAs quantum wells. The light I-V characteristics were measured under AM1.5G at 100 mW/cm2 illumination. The control cell has a Voc of 0.89V and a Jsc of 9.1 mA/cm2. The InAs QD solar cell has a Voc of 0.68 V and a Jsc of 12.2 mA/cm2. The QD cell has about a 33% larger short circuit current density compared to the GaAs control cell, which is mainly due to the higher photon absorption rate related to the DWELL structure. The spectrum response data show that the GaAs control cell and the QD cell have similar external quantum efficiency (EQE) in the visible to near-IR range (400-870nm). Beyond the GaAs absorption edge (870nm), the QD solar cell shows extended response with much higher measured EQE up to ˜1200 nm. This is strong evidence of the contribution from the InAs QDs and InGaAs QWs, the latter being the primary contributor to the increased Jsc.We calculated the “local” ideality factor from measured dark IV data, and then substituted it into a single diode equation to get the “local” reverse saturation current. Whereas the GaAs control shows the typical monotonically decreasing ideality from 0.3 to 0.8V, a linearly increasing ideality is observed in the QD cell. Based on the measured dark currents, and neglecting series resistance, we extrapolated the IV curves to higher voltages and found that they intercept at ˜2×104 mA/cm2. Dividing the intercept point Jdark by the Jsc of the QD cell conservatively estimates the light concentration (˜1400×) above which the QD cell would have a higher Voc than the GaAs cell assuming additivity applies. This result is mainly attributed to the unique carrier transport properties that are introduced into the solar cell devices that utilize QDs.

Selective growth of InP/InGaAs 〈0 1 0〉 ridges: Physical and optical characterization

The selective growth of InP/InGaAs ridges aligned along the 〈0 1 0〉 direction was studied using scanning electron microscopy and photoluminescence measurements. The ridges exhibit very smooth {1 1 0} sidewalls and (0 0 1) top facets. The diffusion of the group III species from the sidewalls to the top (0 0 1) surface was modelled to provide a predictive tool for determining ridge growth, and the optical properties of InGaAs QWs incorporated in the ridges. No growth occurs on the {1 1 0} sidewalls until the ridges complete due to the diffusion of In species to the top (0 0 1) facet. The situation for Ga is quite different, with no diffusion off the {1 1 0} facets observed, and little or no Ga being incorporated on the {1 1 0} surface before or after ridge completion.

Low threshold current density, highly strained InGaAs laser grown by MOCVD

It is possible to delay the growth mode transition from a 2-D growth mode to 3-D growth mode (the so-called Stranski–Krastanov growth mode) by means of non-equilibrium growth process employing a low growth temperature and a high growth rate, and adopting a high V/III ratio simultaneously to maintain crystal quality. Record emission wavelengths in multiple InGaAs/GaAs quantum wells without a strain-compensated barrier are grown by metal organic chemical vapor deposition (MOCVD). An InGaAs vertical-cavity surface emitting laser (VCSEL) with emission spectrum up to 1.26 μm under CW operation has been realized. Optimizing the quality of InGaAs QWs leads to a low threshold current density. The qualities of the highly strained InGaAs QWs of this VCSEL structure, such as internal quantum efficiency, internal loss, and transparency current density, were investigated by standard broad area (BA) laser process. Combined with an extensive gain-cavity detuning and the high-quality InGaAs QWs, the InGaAs VCSEL, we believe, is a promising candidate for application to long wavelength, low-cost source fiber-optical communication systems.

Design of two-dimensional photonic-crystal mirrors for InGaAs QW laser applications

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Design of two-dimensional photonic-crystal mirrors for InGaAs QW laser applications

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Strained InAsN/InGaAs/InP multiple quantum well structures grown by RF-plasma assisted GSMBE for mid-infrared laser applications

The authors report the growth, structural and optical characteristics of strained 10-period InAs1−xNx/In0.53Ga0.47As multiple quantum well (MQW) structures on InP substrates grown by gas-source molecular beam epitaxy. Atomic nitrogen was generated using a RF-plasma cell. Double crystal X-ray diffractometer (DXRD) measurements indicated that adding N to the InAs layer reduced the net compressive strain of the MQW. The highest nitrogen composition obtained in this study was 19.5%. It was also found that the incorporation of nitrogen resulted in red-shifted photoluminescence (PL) emission energy of the QWs. However, increased nitrogen composition broadened the DXRD linewidth and degraded PL intensity. The very broad PL linewidth might be related to alloy inhomogeneity. Finally, ridge waveguide lasers with different periods (n=2–8) of InAs0.97N0.03/InGaAs QWs as the gain medium were fabricated. A device with four QWs gave the best performance and demonstrated pulsed oscillation up to 260K at an emission wavelength of 2.38 µm with a threshold current density of 3.6 kA/cm2. This indicates the potential of InAsN as a material for mid-infrared applications.

Highly strained very high-power laser diodes with InGaAs QWs

With the aim of realizing laser diodes in the wavelength range beyond 1100 nm on GaAs, we have studied the indium incorporation behaviour into pseudomorphic InGaAs-quantum wells with extremely high indium content grown by metalorganic vapour phase epitaxy. A wide growth temperature range between 490°C and 770°C as well as the dependence on V/III-ratio and strain compensation has been studied. At the maximum In-content of 41%, a photoluminescence wavelength of 1238 nm at room temperature is obtained. Laser diodes with an emission wavelength up to 1206 nm were processed. Structures with a slightly reduced In-content, emitting at 1120 nm, were processed to broad-area devices (100 μm×1000 μm) and show output powers up to 12 W, which corresponds to a record high internal power density of 23 MW/cm 2, with a good reliability. LOC structures with a reduced far field below 30° and a higher indium content emit 8.5 W at 1170 nm.

Er-related luminescence in Er,O-codoped InGaAs/GaAs multiple-quantum-well structures grown by organometallic vapor phase epitaxy

We have grown Er,O-codoped InGaAs/GaAs multiple-quantum-well (MQW:Er,O) structures by low-pressure organometallic vapor phase epitaxy (OMVPE), and investigated their luminescence properties. The MQW structures are designed to emit light at 0.98 μm for direct excitation of Er ions. Degradation of the structures due to introduction of Er and oxygen is not observed in x-ray diffraction patterns. Er ions doped with oxygen exhibit a sharp and well-ordered photoluminescence spectrum predominantly from one kind of Er center (Er-2O center). Photoluminescence excitation measurements on MQW:Er,O and Er,O-codoped GaAs samples reveal that under below-GaAs-band-gap excitation (830–940 nm), the Er-related luminescence is observed only in the MQW:Er,O sample. It indicates that the luminescence originates from Er ions in InGaAs QWs by means of trap-mediated excitation process.

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T0. Maximum output powers of 7 W CW are obtained from 4 mm long devices.

Low Pressure OMVPE Grown Compressive Strained Ingaas QWS Surrounded by Tensile Strained Ingaas Spacers

AbstractThe photoluminescence (PL) measurement of unstrained and compressive strained InxGa1−xAs quantum wells (QWs) demonstrated that the interfaces had a roughness of 1 to 2.5 monolayers (ML). The spacer layers of tensile strained InyGa1−yAs were inserted between a compressive strained In0.7Ga0.3As QW and the InP barrier layers. PL spectra of the In0.7Ga0.3As/InyGa1−yAs/InP structures grown at 605°C became significantly narrower with increasing Ga content in the spacer layers above (1−y)=0.6. The PL line width of the In0.7Ga0.3As/In0.3Ga0.7As alternatingly strained multiple quantum well (MQW) structures gradually decreased when the number of periods and the deposition temperature increased. The structure, consisting of 4 periods grown at 635°C, exhibited a PL line width of about 4 meV which corresponded to the QW thickness fluctuation of 0.5 ML. The superlattice satellites of X-ray rocking curves of MQW structures were better defined under an envelope corresponding to the tensile strained layers.

Molecular beam epitaxial growth of In 0.65Ga 0.35 As quantum wells on GaAs substrates for 1.5 μm exciton resonance

A novel approach of growing high quality In 0.65Ga 0.35As multiple quantum wells (MQWs) with Al 0.33Ga 0.67As barriers on GaAs substrates by molecular beam epitaxy (MBE) is reported for optical devices operating near 1.5 μm at room temperature. Operation at 1.5 μm requires InGaAs QWs with very large lattice mismatch to the GaAs substrates (4.7% in this study). The best quality MQWs were achieved by adding one monolayer of GaAs smoothing layers with growth interruptions at the interfaces of both sides of the InGaAs wells and by growing at a very low temperature (280∘C) compared to the buffer layers and typical InGaAs layer growth temperatures (450∘C). The MQW region was grown on a linearly-graded InGaAs buffer layer with a 10% / μm grading rate which was fully relaxed, very smooth, and completely defect-free at the top region. This sample showed a sharp exciton peak near 1.5 μm at room temperature. Cross-section transmission electron microscopy (XTEM), four crystal X-ray diffractometry, and optical absorption measurement were used to characterize the MQW structures.