Low-threshold 833-nm GaAsP-AlGaAs tensile-strained quantum-well laser diodes

We report the demonstration of TM polarized laser emission at 833 nm from GaAsP-AlGaAs quantum well laser structures grown on GaAs substrates by low-pressure organometallic vapor phase epitaxy for the first time. This is the longest wavelength near infrared TM polarized laser ever reported. Broad area laser diodes containing single GaAs/sub 0.95/P/sub 0.05/ quantum well lased at a low threshold current density of 280 A/cm/sup 2/ for a cavity length of 1 mm and with a high differential quantum efficiency of 32%/facet for cavity length less than 500 /spl mu/m.     

Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 μm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm⁻¹ (for λ≈1.08 μm) in an asymmetric waveguide 4 μm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm⁻¹ was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 μm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-μm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 12, 2004, pp. 1477–1486. Original Russian Text Copyright ? 2004 by Slipchenko, Vinokurov, Pikhtin, Sokolova, Stankevich, Tarasov, Alferov.     

Low-threshold laterally oxidized GaInP-AlGaInP quantum-well laserdiodes

Low-threshold, high-efficiency edge-emitting visible AIGaInP-GaInP laser diodes using a buried AlAs native oxides for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers operate with room temperature, continuous-wave (CW) threshold currents of 11 mA with external differential quantum efficiency of 34% per facet for an uncoated 300-μm-long 3.5-μm-wide device. As-fabricated lasers exhibited modest performance under CW operation. Post-fabrication annealing was shown to dramatically improve the device characteristics     

High-power laser diodes based on asymmetric separate-confinement heterostructures

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ～1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ～100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm^?1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T ₀= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.     

Theory of non-Markovian gain in strained-layer quantum-well laserswith many-body effects

A non-Markovian model for the optical gain of strained-layer quantum-well lasers is developed taking into account the valence-band mixing, strain effects, many-body effects, and the non-Markovian relaxation using the time-convolutionless reduced-density operator formalism given in previous papers for an arbitrary driven system coupled to a stochastic reservoir. Many-body effects are taken into account within the time-dependent Hartree-Fock approximation and the valence-band structure is calculated from the 6×6 Luttinger-Kohn Hamiltonian. The optical gain with Coulomb (or excitonic) enhancement is derived by integrating the equation of motion for the interband polarization. It is shown that the vertex function for the interband polarization can be obtained exactly without relying on the Pade approximation. As a numerical example, an In_xGa_1-xAs-InP quantum well (QW) is chosen for its wide application in optical communication systems. It is predicted that the Coulomb enhancement of gain is pronounced in the cases of compressive and unstrained QWs while it is negligible in the case of tensile strained QW     

Multiple-wavelength integration in InGaAs-InGaAsP structures using pulsed laser irradiation-induced quantum-well intermixing

In this paper, we present the characteristics of a quantum-well intermixing technique using pulsed-photoabsorption-induced disordering. Photoluminescence, micro-Raman spectroscopy, and transmission electron microscopy were used to characterize the process. Using this technique, a differential wavelength shift between the intermixed and nonintermixed regions of over 160 nm has been observed from InGaAs-InGaAsP heterostructures. It was found from the micro-Raman measurements that a spatial resolution of better than 2.5 /spl mu/m can be achieved. A theoretical model has been developed to estimate the spatial resolution limit. Theoretical analysis has also been performed to investigate the effect of laser irradiation on the degree of intermixing in InGaAs-InGaAsP structures. To verify the capability of this process in monolithic photonic integration, high-quality bandgap tuned lasers, two-section extended cavity lasers, and multiple-wavelength laser chips have been fabricated.     

Induced disorder of AlAs-AlGaAs-GaAs quantum-well heterostructures

The effects of induced disorder on the layered structure and luminescence properties of Al_xGa_1-xAs quantum-well heterostructures (QWH’s) grown at Ts = 750°C by metalorganic chemical vapor deposition (MO-CVD) are investigated. High-temperature thermal anneals in the range 1000–800°C > T_s result in the interdiffusion of Al and Ga and disordering of the QWH active region. Similar results are obtained at the much lower temperature 500–600°C < T₈ by impurity (Zn) diffusion, which greatly enhances the Al-Ga interdiffusion process. It is also possible, by the use of a Si₃N₄ surface mask, to disorder selectively only certain portions of a QWH, thus leaving unchanged the as-grown quantum-well layered structure in the remaining areas. Lower-bandgap QWH’s can be dis ordered and changed into higher-bandgap material, including from direct gap to indirect gap     

Multichannel carrier scattering at quantum-well heterostructures

An efficient combined numerical-analytical technique is developed for calculating states of the continuum spectrum in systems with quantum wells (QWs) with an arbitrary potential shape, described by a system of coupled Schrödinger equations, e.g., hole states in semiconductor QWs. Continuum-spectrum states are found exactly using the approach similar to the scattering theory. Scattering states (the in/out-solutions) and the S-matrix for the case of multichannel scattering in one-dimensional systems with QWs are constructed, and their symmetry is determined and analyzed. The method is applied to studying the hole scattering by GaInAs-InGaAsP QWs with strained layers. The hole transmission and reflection coefficients and the delay-time energy dependence are calculated in relation to parameters of the structures and values of the transversal momentum components. In the energy range in which the channel with heavy hole conversion into a propagating light hole is closed, scattering of the heavy hole on a QW has a resonant nature.     

Imperfections and resonant tunneling in quantum-well heterostructures

We discuss effects of structural imperfections on the I-V characteristics and local density-of-states of semiconductor double-barrier heterostructures. Using a linear-chain model for GaAs/AlGaAs structures, we simulate fluctuations in layer thicknesses, defects at the heterointerfaces, and disorder.     

Small-chirp 40-Gbps electroabsorption modulator with novel tensile-strained asymmetric quantum-well absorption layer

A small-chirp 40-Gbps electroabsorption modulator (EAM) with a novel tensile-strained asymmetric quantum-well (QW) absorption layer has been demonstrated for the first time. The strain and the band line-up of the asymmetric QW structure were designed in order to obtain a small-chirp operation, a clear eye opening, and a high extinction ratio simultaneously. The chirp measured as /spl alpha/-parameter was reduced without any penalty of extinction ratio and eye opening. The measured /spl alpha/-parameter was smaller than 1.5 at any bias voltage from 0 to -2 V. The measured 3-dB bandwidth of a 75-/spl mu/m-long EAM exceeded 50 GHz at -1 V bias voltage. Under a 40-Gbps modulation, a clear eye opening was obtained, and the eye diagram showed no violation of the standard STM256/OC768 mask. The measured dynamic extinction ratio was over 11 dB.     

780 nm band TM-mode laser operation of GaAsP/AlGaAs tensile-strained quantum-well lasers

Tensile-strained active layer GaAs/AlGaAs separate-confinement-heterostructure quantum-well lasers are reported. These lasers oscillate in the 780 nm band in the TM mode by TM mode gain enhancement in the tensile-strained active layer. The threshold current density of single-quantum-well laser diodes increases rapidly with heatsink temperature. However, triple-quantum-well laser diodes with a cavity length of 485-110 mu m oscillated with a threshold current density of 1.4 and 3.0 kA/cm/sup 2/.<>     

Enhanced bandgap resonant nonlinear susceptibility in quantum-well heterostructures

Calculation shows that the bandgap resonant nonlinear susceptibility in a multi-quantum-well structure can be a factor of approximately 2 greater than in the bulk. The calculation uses the mechanism of blocking of band-to-band transitions, likely to be present in materials of interest for advanced optical-fibre communication systems.     

Optical characteristics of quantum-well heterostructures in saturation conditions

The resalts of theoretical investugation for spectral characterstics of gain, refraction index of QW heterostructures depending on quantum layer thickness the value of saturation field, as well as their field dependence are presented.     

Spin injection in GaAs/GaSb quantum-well heterostructures

GaAs/GaSb type-II quantum-dot heterostructures were grown by molecular-beam epitaxy. The circularly polarized photoluminescence of these samples in a magnetic field up to 4.7 T in the Faraday configuration was investigated. It was found that the emission from quantum dots in a magnetic field is σ⁻-polarized, which corresponds to the electron-spin component along the magnetic-field vector of +1/2. The degree of polarization increases with increasing excitation intensity. The observed effect is explained in terms of spin injection from the GaSb matrix, where spin orientation appears owing to the Zeeman splitting of the conduction band. An increase in the degree of polarization occurs due to a reduction in the charge-carrier radiative lifetime in type-II quantum dots with increasing excitation level.     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

Low-threshold current density 1.3-μm InAs quantum-dot laserswith the dots-in-a-well (DWELL) structure

The wavelength of InAs quantum dots in an In_0.15Ga_0.85As quantum-well (DWELL) lasers grown on a GaAs substrate has been extended to 1.3-μm. The quantum dot lasing wavelength is sensitive to growth conditions and sample thermal history resulting in blue shifts as much as 73 nm. The room temperature threshold current density is 42.6 A cm^-2 for 7.8-mm cavity length cleaved facet lasers under pulsed operation     

2.0-/spl mu/m single-mode operation of InGaAs-InGaAsP distributed-feedback buried-heterostructure quantum-well lasers

Distributed-feedback (DFB) buried-heterostructure (BH) lasers with quantum-well active region emitting at 2.0 /spl mu/m have been fabricated and characterized. The lasers with four wells showed performance of practical use: threshold current as low as 15 mA for 600-/spl mu/m-long devices and CW single-mode output up to 5 mW at 2.03 /spl mu/m under operation current of 100 mA were observed. The current- and temperature-tuning rates of DFB mode wavelength are 0.004 nm/mA and 0.125 nm/K, respectively.     

A novel cladding structure for semiconductor quantum-well laserswith small beam divergence and low threshold current

A novel cladding structure is proposed and analyzed for semiconductor quantum-well lasers to achieve a small vertical-beam divergence and a low threshold current density simultaneously. This cladding structure is designed to guide a wide optical mode but with a high peak intensity in quantum wells. The wide expansion of the optical mode results in a small beam divergence. In addition, the high optical Intensity in quantum wells causes a low threshold current density. This novel cladding structure is optimized. The result shows that this type of cladding structures can achieve a beam divergence as small as 14.6° while the threshold current density remains small     

Low-threshold InGaAs/GaAs strained-layer surface emitting laserswith two 45° angle etched total reflection mirrors

Summary form only given. An InGaAs/GaAs strained-layer IPSEL (in-plane surface emitting laser) structure with two 45° dry-etched mirrors and a highly reflecting bottom quarter-wavelength stack is reported. It has a record low continuous-wave (CW) threshold current at 10 mA. The laser structure consists of a conventional double-heterostructure single-quantum-well (80-Å In_0.2Ga_0.8As/100-Å GaAs) laser structure on top of a quarter-wave stack (25 pairs of 695-Å GaAs/830-Å AlAs), which serves as a distributed Bragg reflector (~99%) after 45° angle etching     

Spectra of persistent photoconductivity in InAs/AlSb quantum-well heterostructures

Persistent photoconductivity at T = 4.2 K in AlSb/InAs/AlSb heterostructures with two-dimensional (2D) electron gas in InAs quantum wells is studied. Under illumination by IR radiation (?ω = 0.6–1.2 eV), positive persistent photoconductivity related to the photoionization of deep-level donors is observed. At shorter wavelengths, negative persistent photoconductivity is observed that originates from band-to-band generation of electron-hole pairs with subsequent separation of electrons and holes by the built-in electric field, capture of electrons by ionized donors, and recombination of holes with 2D electrons in InAs. It is found that a sharp drop in the negative photoconductivity takes place at ?ω > 3.1 eV, which can be attributed to the appearance of a new channel for photoionization of deep-level donors in AlSb via electron transitions to the next energy band above the conduction band.