InAlGaAs Quantum Research Articles

Effect of GaInP and GaAsP inserted into waveguide/barrier interface on carrier leakage in InAlGaAs quantum well 808-nm laser diode

Effect of GaInP and GaAsP inserted into waveguide/barrier interface on carrier leakage in InAlGaAs quantum well 808-nm laser diode

Effect of GaInP and GaAsP inserted into waveguide/barrier interface on carrier leakage in InAlGaAs quantum well 808 nm laser diode

Effect of GaInP and GaAsP inserted into waveguide/barrier interface on carrier leakage in InAlGaAs quantum well 808 nm laser diode

Morphological and optical characterization of self-assembled InAlGaAs/GaAs quantum dots

This experimental study reports the morphological and optical properties of self-organized quaternary InAlGaAs quantum dots (QDs) grown on GaAs substrates. Atomic force microscopy (AFM) revealed the presence of QDs and their geometry across the sample surface, while the optical properties were verified by photoluminescence (PL) spectroscopy. Temperature-dependent PL measurements were performed for a series of samples with different indium compositions. Unlike conventional quantum well materials, the change in PL peak positions in QD structures exhibits a non-monotonic exotic dependence on temperature. Our AFM data confirm a bimodal distribution of dot sizes as corroborated by calculated thermal activation energies. A rapid decrease in the PL signal at elevated temperatures suggests that thermionic emission and interface defects are the two dominant mechanisms of carrier escape and recombination in these QD structures. Such a quaternary QD-based active region is important for realizing next-generation diode lasers with an emission wavelength shorter than 1 μm.

Vertical Hybrid Integration Devices Using Selectively Defining Underneath Si Waveguide

3D hybrid integration based on III-V/Si waveguides by selective undercut wet etching (SUWE) of the lower Si layer has been demonstrated on a silicon-on-insulator (SOI) template. The process was performed on an adhesive-bonding material structure, defined by the upper InP/InAlGaAs (InAlGaAs quantum well) p-i-n heterostructure and the lower 220 nm SOI. After the top p-i-n III-V tapered waveguide was first fabricated and covered by Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , KOH was then used for SUWE of Si layer from SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , forming the bottom SOI single-mode waveguide. In comparison to monolithic III-V waveguide structure (InP based material), the simulated confinement factor of active region shows an enhancement from 10.3% to 16.7%. SOA/EAM devices were also processed and integrated in III-V layer, showing 7.2 dB optical gain at 70 mA injection current in SOA and 21.7 dB extinction ratio within 0~−2 V swing voltage in EAM. The strong quantum confined Stark effect (QCSE) in MQW confirms the improved confinement factor. It suggests a vertical self-alignment scheme could be used for realizing compact and submicron scale heterogeneous integration in a Si photonics template.

Influence of growth conditions on the quality of strained InAlGaAs/AlGaAs quantum wells grown by MOCVD

Compressive-strained InAlGaAs quantum wells (QWs) were grown on GaAs substrates by metal organic chemical vapor deposition (MOCVD). The influences of reactor pressure, V/III ratio, growth temperature, and substrate orientation on the quality of InAlGaAs QWs were studied using high resolution X-ray diffraction (HR-XRD), photoluminescence (PL) and atomic force microscope (AFM) measurements. The PL results indicate that the PL intensity and full width at the half-maximum (FWHM) of QWs are very sensitive to the growth conditions such as reactor pressure, growth temperature, and substrate orientation. The AFM results demonstrate that the growth mode of epilayer is dominated by the orientation of substrate. The growth mode of samples grown on 0.5° miscut and 2° miscut substrates is step flow and step bunching, respectively. The samples grown on 0.5° miscut substrates have higher PL intensity comparison with the samples grown on 2° miscut substrates at the same growth conditions. The PL and AFM results of sample grown at 700 °C and a pressure of 50 mbar with a V/III ratio of 100 indicated that these growth parameters are close to the optimum growth conditions for InAlGaAs QWs.

Spin polarization modulation for high-speed vertical-cavity surface-emitting lasers

The spin polarization modulation in birefringent vertical-cavity surface-emitting lasers (VCSELs) is investigated theoretically and experimentally for obtaining tailored polarization modulation characteristics suitable for high-speed data communications. A spin-flip rate equation analysis reveals that the spin polarization modulation response of VCSELs is flattened by shortening the electron spin relaxation time and its 3-dB bandwidth is broadened to a range determined by a frequency split between two orthogonal polarization modes. Optical modulations of spin polarized electrons in commercially-available InAlGaAs quantum well VCSELs demonstrate a wide 3-dB bandwidth of 23 GHz determined by the frequency split, which indicates that the spin relaxation time in the InAlGaAs quantum well VCSEL is around 20 ps at room temperature and suitable for use in high-speed data communications at a telecom wavelength of 1.55 μm.

Lasing Polarization Characteristics in 1.55- $\mu \text{m}$ Spin-Injected VCSELs

Circular polarization characteristics in vertical-cavity surface-emitting lasers (VCSELs) with InAlGaAs quantum wells injected by spin-polarized electrons were investigated. A degree of circular polarization of 10% was obtained in a reduced birefringence VCSEL at a lasing wavelength of 1544 nm at room temperature under optical pumping of spin-polarized electrons. Strong birefringence originally introduced to stabilize the lasing polarization was confirmed to be undesirable for a high degree of circular polarization in spin-injected VCSELs. A spin-flip rate equation analysis fairly reproduced the experimental results and supported our conclusions.

Intra-cavity patterning - new method of single mode emission enhancement

We demonstrate the results of numerical simulations of 1.3μm InAlGaAs/InP VCSEL with a ring pattern etched at the interface between the cavity and top DBR. We show that the proposed design offers selective confinement of the fundamental mode and strong discrimination of higher order modes. Consequently, VCSEL with ring confinement is capable to operate in a broad range of injected currents in the single mode regime, which facilitates the improvement of maximal emitted power and increase of the wavelength tuning range with very narrow spectral characteristics. High power, single-mode emitting vertical-cavity surface-emitting lasers (VCSELs) are of great interest, since they can serve as high-power, smoothly tuned with current and temperature, coherent-optical sources. Emerging applications include inexpensive and portable gas sensors, telecommunication emitters, and so on. For these applications, it is preferable to have a low-threshold, high side-mode suppression ratio (SMSR) light source. VCSELs inherently emit in a single longitudinal mode; controlling the lateral mode is far more complicated. It can be achieved using a well-established wet oxidation technology, which makes possible single-mode operation only for relatively narrow apertures (providing less than 5 mW of output power) (1). Other methods provide up to twofold higher emitted power but exploit more challenging technologies (2-5). The limitation of high power single mode operation comes from small optical apertures or multimode operation under high injection levels. This paper provides numerical analysis of the ring pattern etched in the cavity of the VCSEL which eliminates higher order mode emission. The ring pattern provides confinement for a fundamental mode and forces higher order modes to be pushed out of the active region. The analyzed structure (Fig. 1a) (6) incorporates InAlGaAs quantum wells within an InP cavity. The cavity is bounded by 35 pairs of Al0.9Ga0.1As/GaAs DBRs from the bottom and 20.5 pairs of Al0.9Ga0.1As/GaAs DBRs from the top. Laterally patterned tunnel junction (TJ) layers are responsible for tunnelling carriers into the

Comparative study of Photoluminescence variation in InAs Quantum dots embedded in InAlGaAs Quantum wells

Papers in the Appendix were published in electronic format as Volume 1534

A multi-section technique for the electroabsorption measurements in waveguide semiconductor electroabsorption modulators

A technique for measuring the optical absorption spectra of waveguides, semiconductors and electroabsorption modulators is described. The technique uses a multi-sectioned optical waveguide that has electrically isolated longitudinal sections and has a p–i–n cross-section structure. Light generated in forward biased sections is used to probe the optical absorption in sections that can be reverse biased. The technique is applied to a p–i–n electroabsorption device that was designed to operate over a broadband of optical communication wavelengths. It has an active region consisting of multiple-width InGaAs–InAlGaAs quantum wells. For this device, a band edge shift of 40 meV is obtained at an applied field of 105 kV cm−1, and figures of merit Δα, Δα/F and Δα/α0 were also determined as a function of wavelength and applied field, where Δα is the absorption coefficient change due to electroabsorption, α0 static absorption coefficient of the wells at zero bias field and F the applied reverse bias field.

Interdiffused InAs∕InGaAlAs quantum dashes-in-well structures studied by surface photovoltage spectroscopy

We report the study of interband optical transitions in the interdiffused InAs quantum dash (QD) in InAlGaAs quantum well (QW) structures using room temperature surface photovoltage (SPV) spectroscopy. SPV signals have been detected from all relevant portions of both the as-grown and interdiffused structures including the QD, QW, and cladding layer. The effect of group-III intermixing on the interband optical transition energies in the interdiffused structures has also been revealed by the SPV spectroscopy, and the results have been confirmed by photoluminescence measurements. The SPV investigation shows that the compositional intermixing occurs not only between the dash and the surrounding well but also between the well and the surrounding barrier. The results demonstrate the potential of the SPV spectroscopy as a nondestructive, contactless method to characterize optical transitions in complex semiconductor nanostructures at room temperature.

Vertical stacks of shape-engineered InAs∕InAlGaAs quantum dot and its influences on the lasing characteristics

The formation characteristics on the vertical stacks of shape-engineered InAs∕InAlGaAs quantum dots (QDs), which were formed by the alternate growth method (AGQDs), were studied in terms of the modulation in strain field and phase separation. The threshold current of the broad-area laser diodes (LDs) with five stacks of the AGQDs (AGQD-LDs) was 4.5 times smaller than that of the LDs with seven stacks of the conventionally grown QDs (CQD-LDs). The slope efficiency for the AGQD-LDs was 0.16W∕A, which was higher than that of the CQD-LDs of 0.9W∕A. These results can be attributed to better confinement of the electron wave function in QDs.

Experimental evidence on quantum well–quantum dash energy transfer in tunnel injection structures for 1.55μm emission

Here comes a report on the investigation of the energy transfer in InP-based tunnel injection structures, consisting of InAs∕InAlGaAs quantum dashes (QDashes) and an InGaAs∕InAlGaAs quantum well (QW), designed for 1.55μm emission at room temperature. Temperature dependent photoluminescence excitation (PLE) spectroscopy was used to experimentally confirm that the carriers created in the well reach the quantum dash layer by the tunneling through a thin InAlAs∕InAlGaAs barrier and recombine there radiatively. A measurable QW-QDash energy transfer has been detected up to 130K. The electronic structure of the whole complex system obtained by modulation spectroscopy exhibits full conformity with the PLE measurement results.

Surface photovoltage spectroscopy of interdiffused InAs/InGaAlAs quantum dashes‐in‐well structure

AbstractWe report room temperature surface photovoltage (SPV) spectroscopy studies of both as‐grown and interdiffused InAs quantum dash (QD)–in–InAlGaAs quantum well (QW) structures grown by molecular beam epitaxy on (100) InP substrates. The interdiffusion is achieved by means of rapid thermal annealing at 800 ºC for 30 s. The SPV spectra reveal step‐like structures related to the optical absorption in the QDs, QWs, InGaAlAs separate carrier confinement layer, InAlAs lower cladding layer and InP substrate. The annealing results in a high‐energy shift of these spectral structures. The shift is attributed to the group‐III atoms intermixing from the thermal induced interdiffusion across the heterointerfaces. The effect of interdiffusion is larger for the elements with larger surface‐to‐volume ratio (QDs and QWs). The blue shift of the QD transition is observed also in the photoluminescence spectra. The results contribute to the optimization of the technological procedure for QD bandgap tuning via the interdiffusion technique. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Theoretical and experimental analysis on InAlGaAs/AlGaAs active region of 850-nm vertical-cavity surface-emitting lasers

In this study, the gain-carrier characteristics of In/sub 0.02/Ga/sub 0.98/As and InAlGaAs quantum wells (QWs) of variant In and Al compositions with an emission wavelength of 838 nm are theoretically investigated. More compressive strain, caused by higher In and Al compositions in InAlGaAs QW, is found to provide higher material gain, lower transparency carrier concentration, and transparency radiative current density over the temperature range of 25-95/spl deg/C. To improve the output characteristics and high-temperature performance of 850-nm vertical-cavity surface-emitting laser (VCSEL), In/sub 0.15/Al/sub 0.08/Ga/sub 0.77/As/Al/sub 0.3/Ga/sub 0.7/As is utilized as the active region, and a high-bandgap 10-nm-thick Al/sub 0.75/Ga/sub 0.25/As electronic blocking layer is employed for the first time. The threshold current and slope efficiency of the VCSEL with Al/sub 0.75/Ga/sub 0.25/As at 25/spl deg/C are 1.33 mA and 0.53 W/A, respectively. When this VCSEL is operated at an elevated temperature of 95/spl deg/C, the increase in threshold current is less than 21% and the decrease in slope efficiency is approximately 24.5%. A modulation bandwidth of 9.2 GHz biased at 4 mA is demonstrated.

Well-defined excited states of self-assembled InAs∕InAlGaAs quantum dots on InP (001)

Self-assembled InAs∕InAlGaAs quantum dots (QDs) in an InAlGaAs matrix on InP (001) substrates were grown by the alternate growth method (AGQD), where an InAs layer with a thickness of 1 monolayer (ML) and an InAlGaAs layer with a thickness of 1 ML were alternately deposited. Cross-sectional transmission electron microscopy images indicated that the aspect ratio (height/width) for the AGQDs was ∼0.25, which was higher than ∼0.10 of conventionally grown InAs QDs. The photoluminescence (PL) peak position for the ground states of the AGQDs was 1.485μm with a linewidth broadening of 42meV at room temperature, while the PL linewidth for the conventionally grown QDs was 85meV. And the peaks for the excited-state transitions were also clearly observed from the excitation-power dependent PL. This is the first observation on the well-defined excited-state transitions from the InP-based InAs QDs, even though there were several reports on the features of the excited states.

Sub-mA threshold 1.5-μm VCSELs with epitaxial and dielectric DBR mirrors

In this letter, we report low threshold 1.5-/spl mu/m vertical-cavity surface-emitting lasers with epitaxial and dielectric distributed Bragg reflector (DBRs). The device consists of a lattice-matched InAlAs-InAlGaAs DBR grown on an InP substrate, an InAlGaAs quantum well active region, a metamorphic GaAs tunnel junction, and a SiO/sub 2/-TiO/sub 2/ dielectric DBR. The current confinement is achieved by oxidizing an AlAs metamorphic layer grown on top of the active region. Small aperture devices show a minimum threshold of 0.8 mA at room temperature in continuous-wave operation.

Homogeneous linewidth of self-assembled III–V quantum dots observed in single-dot photoluminescence

We report photoluminescence emission from single self-assembled InAlGaAs quantum dots, which is broadened purely by dephasing processes. We observe linewidths as low as 6±3 μeV at 10 K , which agrees with the homogeneous linewidth derived from four-wave mixing experiments. By selecting dots that are not affected by local field fluctuations and using high-energy excitation, we avoid additional sources of linewidth broadening typically present in single-dot photoluminescence spectra. We observe a strong LO–phonon coupling in InAlGaAs and InGaAs dots, which becomes the dominating contribution to the linewidth above 50 K .

Dephasing in Self-organized InAlGaAs Quantum Dots

We report the first direct measurements of dephasing in III-V semiconductor quantum dots at low temperature using degenerate four-wave mixing. At 0 K, the coherence time is limited by the population lifetime whereas pure dephasing due to exciton-phonon interactions appears only at finite temperatures. We observe a striking discrepancy between the homogenous linewidth derived from the dephasing times and the measured photoluminescene linewidth of individual quantum dots, indicating the presence of an additional inhomogenous broadening mechanism in photoluminescence measurements of single quantum dots.

Second-harmonic scanning optical microscopy of semiconductor quantum dots

Second-harmonic (SH) optical imaging of self-assembled InAlGaAs quantum dots (QD's) grown on a GaAs(0 0 1) substrate has been accomplished at room temperature by use of respectively a scanning far-field optical microscope in reflection mode and a scanning near-field optical microscope in transmission mode. In both cases the SH signal peaks at a pump wavelength of ∼885 nm in correspondence to the maximum in the photoluminescence spectrum of the QD sample. SH near-field optical images exhibit spatial signal variations on a subwavelength scale that depend on the pump wavelength. We attribute this feature to inhomogeneous broadening of the QD energy states.