Heterostructure Laser Diodes Research Articles

Numerical drift‐diffusion simulation of Auger hot electron transport in Ingaasp/Inp double heterojunction laser diodes

AbstractThis paper considers the adaptation of drift‐diffusion device simulation methodology to study Auger‐recombination‐induced hot electron transport characteristics in InGaAsP/InP double heterostructure laser diodes. In order to model the transport behaviour of the Auger hot electrons, we decompose the conventional electron current continuity equation into two components, with one for the Auger hot electrons and the other for the low‐energy electrons. These equations, which use the energy relaxation time parameter to model the dynamics of the Auger hot electrons, are then coupled with the hole current continuity equation and the Poisson equation to obtain self‐consistent solutions. Results from the case studies of one‐dimensional N‐p‐P InGaAsP/InP double heterojunction laser diodes with material composition corresponding to 1·3 μm and 1·55 μm wavelength emissions are presented. We have observed that hot electrons generated through Auger recombination inside the active region can spread into both the N‐ and the P‐InP cladding layers. Within the drift‐diffusion framework, it is demonstrated that the hot electron concentration in the N‐InP cladding layer can be five orders of magnitude higher than that in the P‐InP cladding layer. Because energy transport of the hot electrons in not modelled under the drift‐diffusion approximation, the simulated results are discussed to highlight some of the possible limitations in using drift‐diffusion physics to study Auger hot electron transport behaviour. The importance of taking energy transport into account is emphasized.

Buried-oxide ridge-waveguide InAlAs-InP-InGaAsP (λ∼1.3 μm) quantum well heterostructure laser diodes

Native oxide technology is used to fabricate long wavelength (λ∼1.3 μm) InAlAs-InP-InGaAsP quantum well heterostructure laser diodes with a buried oxide undercutting and constricting the ridge-waveguide active region. The buried native oxide of InAlAs constricts the current and reduces edge and surface losses. Data are presented showing threshold currents as low as ∼140 mA for ∼13-μm-wide stripes (L∼750 μm), with maximum continuous wave output powers as high as ∼225 mW/facet and external differential quantum efficiencies up to 67% (300 K, uncoated facets).

2.7–3.9 μm InAsSb(P)/InAsSbP low threshold diode lasers

Lasing has been obtained in the wavelength range 2.7–3.9 μm in double heterostructure diode lasers with an active region made of InAs alloys. The devices were grown by liquid-phase epitaxy. Typical values of threshold current at 80 K were as low as 40 mA and the maximum operating temperature was 180 K. The blue shift of lasing modes was observed with current. This was explained by the increase of the carrier density in the active region above threshold due to intervalence band absorption.

Gain and dynamics in ZnSe-based quantum wells

Gain spectroscopy and population dynamics are investigated in ZnCdSe/ZnSSe/ZnMgSSe separate confinement heterostructure (SCH) diode lasers. Both steady state and time-resolved methods are applied to characterize the dense electron-hole pair gas in the ZnCdSe active quantum well (QW) region from 77 K to room temperature. Effects due to the carrier interaction with optical phonons and electron-hole Coulomb effects are discussed. A direct measurement of the carrier lifetime at pair densities under typical laser conditions has also been obtained.

Stress distributions and defect nucleation in buried heterostructure laser diodes

Shear stress distributions, arising at the corners of the active region of buried heterostructure laser diodes, are calculated for a given mismatch and various dimensions of the buried stripe and also for a single and a multiple quantum well structure. The locations of high stresses are compared to the nucleation sites of shear stress induced defects, as observed by transmission electron microscopy in real lasers. The implications of the defects are illustrated and discussed for the case of an overstress tested diode as well as possibilities to prevent the defect formation.

Finite element analysis for lossy optical waveguides by using perturbation techniques

A finite element analysis, based on the variational procedure, is used to find the modal loss or gain for both the TE and TM modes with the application of the perturbation technique. Results for the modal gain for the buried heterostructure diode laser are presented, as well as the loss estimation for both the TE and TM modes for the asymmetrical multilayer metal-clad planar optical waveguides. The results obtained agree very well, for a wide range of loss/gain values, with the previously published work using alternative approaches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Long wavelength (λ∼1.5 μm) native-oxide-defined InAlAs-InP-InGaAsP quantum well heterostructure laser diodes

Native oxidation (‘‘wet’’ oxidation via H2O vapor+N2) of InAlAs is employed to fabricate long wavelength (λ∼1.5 μm) InAlAs-InP-InGaAsP quantum well heterostructure laser diodes. Data are presented on gain-guided native-oxide-defined stripe-geometry lasers (40 μm×500 μm) with threshold currents of 200 mA (1 kA/cm2) emitting with multiple longitudinal modes centered at λ∼1.5 μm. The threshold currents, approximated as Ith=I0 exp(T/T0), exhibit a characteristic temperature of T0∼49 K and an operating temperature as high as T=70 °C. Maximum continuous output powers of 140 mW/facet (uncoated facets) and a differential quantum efficiency of 38% are achieved.

Molecular beam epitaxy growth of pseudomorphic II–VI multilayered structures for blue/green laser diodes and light-emitting diodes

This article reports results involving the molecular beam epitaxial growth of the quaternary (Zn,Mg)(S,Se) compound as well as the incorporation of this quaternary into a pseudomorphic separate confinement heterostructure laser diode configuration. It was found that the quaternary (Zn,Mg)(S,Se) can accommodate much more strain as compared to binary ZnSe; the films remained essentially pseudomorphic, with low defect densities, for strains in the studied range from −0.225% (tension) to 0.137% (compression) at room temperature. The relationship between the surface morphology and the strain is also described in this paper. Lasing was routinely obtained at room temperature under pulsed injection. A threshold lasing voltage of as low as 7 V was observed in index-guided diode lasers.

Guided modes and far-field patterns of lead chalcogenide buried heterostructure laser diodes

The far-field of several PbSe/PbEuSe buried heterostructure (BH) laser diodes has been measured. An algorithm for the calculation of the propagation constant and transverse mode function of waveguide structures has been used to calculate the near- and far-field pattern. The theoretical and experimental results are presented and compared with each other. Polarization measurements in the far-field show simultaneous emission of transverse electric (TE) and transverse magnetic (TM) modes from some of the laser diodes.

Peculiarities of catastrophic optical damage in single quantum well InGaAsP/InGaP buried-heterostructure lasers

For investigation of the catastrophic optical damage (COD) of InGaAsP material systems emitting at 0.8 μm, separate-confinement-heterostructure single-quantum-well structures grown on (100) GaAs substrate by liquid-phase epitaxy were mesa-etched for buried heterostructure (BH) laser diodes. The single mode InGaAsP/InGaP diodes were cw operated at room temperature. The measured COD level of a BH InGaAsP/InGaP laser with a cavity length of 470 μm was 8.6±0.7 (MW/cm2). Particularly, we could not observe COD in the long cavity InGaAsP/InGaP lasers, but they showed thermal saturation which is reversible. Also, InGaAsP lasers were found to sustain high current injection three times more strongly than AlGaAs counterparts.

MOVPE growth of strained InAsP/InGaAsP quantum-well structures for low-threshold 1.3-μm lasers

Device-quality strained InAsP/InGaAsP multiple-quantum-well (MQW) structures are successfully grown using the low-pressure metalorganic vapor phase epitaxy method. The grown MQW structures are characterized using X-ray, photoluminescence, and photocurrent measurements that confirm that their structural and optical qualities are high enough for practical device applications, as well as that the InAsP/InGaAsP heterostructures have a large conduction-band offset. The grown wafers are processed into 40-/spl mu/m-wide stripe-ridge waveguide lasers. Threshold current densities as low as 88 A/cm/sup 2/ are achieved for a graded-index separate-confinement heterostructure (GRIN-SCH) single-quantum-well laser diode. Buried heterostructure laser diodes fabricated from GRIN-SCH 4-well strained MQW wafers have threshold currents as low as 1.05 mA at 26/spl deg/C and 7.2 mA at 106/spl deg/C.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

20 GHz Bandwidth High Dynamic Range 1.3 μm Buried Heterostructure Laser Modules

A 20 GHz bandwidth 1.3 μ InGaAsP/InP Straight-Wall Mass-transport Buried Heterostructure laser diode was developed to operate in a microwave fiber optic link. When used in a microwave link, the laser has a typical RF insertion loss of 37 dB, an equivalent input noise density less than -115 dBm/Hz, a 1 dB compression dynamic range greater than 138 dB.Hz and a spurious signal free dynamic range of 97 dB.Hz 2/3 . The wide bandwidth, high dynamic range and low-noise of the laser module were obtained through the design of the package, the subcarrier and the laser chip

Suppression of Side‐Etching in C 2 H 6 / H 2 / O 2 Reactive Ion Etching for the Fabrication of an InGaAsP / InP P‐Substrate Buried‐Heterostructure Laser Diode

A reactive ion etching (RIE) technique using a , , and mixture was applied to the fabrication of (P‐substrate partially inverted buried heterostructure laser diodes, which have been commercially produced for their superior characteristics. The addition of suppressed side etching and made it possible to fabricate ridge mesa structures for the laser diodes with a height of 4 μm and a width of 1 μm with superior controllability. The effects of addition were investigated by Auger electron spectroscopy and a mechanism suppressing side etching was examined. The characteristics including lifetime of the laser diodes fabricated by the RIE technique were as excellent as those of laser diodes fabricated by wet etching.

Far-field solution of the Helmholtz equation for double heterostructure diode lasers

On the basis of the Helmholtz equation the far-field distribution is derived for double heterostructure lasers. The results show that the far-field distribution in the direction normal to the junction plane approaches a Lorentzian function, but parallel to the junction it may be approximated by a Gaussian function. The far-field intensity patterns have “analogous elliptic” form. It is also shown, for the first time, that the separability condition is not strictly valid for the far-field of a laser diode. Only in the vicinity of the optical axis the field can be expressed as a product of two separate functions, each of which depends only on one of the two transverse coordinates parallel and perpendicular to the diode junction.

Novel surface emitting GaAs/AlGaAs laser diodes based on surface mode emission

We present a novel concept to achieve surface emission from conventional semiconductor laser diodes. This new type of laser diode is modified to allow a coupling of the laser mode to a transverse electric polarized surface mode. As a result we achieve surface emission from GaAs/AlGaAs double heterostructure laser diodes with a beam divergence of 0.2%. This novel concept has a high potential for the realization of a beam steering device.

Room temperature continuous operation of blue-green laser diodes

Continuous-wave operation in wide-gap II-VI semiconductor current injection laser diodes at room temperature has been demonstrated for the first time. Stimulated emission was observed at a wavelength of 523.5 nm with a threshold current of 45 mA (1.4 kA/cm2) from ZnCdSe/ZnSe/ZnMgSSe single-quantum-well (SQW) separate-confinement heterostructure (SCH) laser diodes.

1.3 mu m multiquantum well decoupled confinement heterostructure (MQW-DCH) laser diodes

A 1.3- mu m multi-quantum-well decoupled confinement heterostructure (MQW-DCH) laser diode has been developed. This structure introduces internal barriers between the active quantum wells and the optical waveguide. It is thus possible to have, at the same time, deep quantum wells to prevent carrier leakage and a strong optical waveguide with a high confinement factor. The barrier parameters have been optimized using numerical modeling tools, and the DCH laser diode has been built using chemical beam epitaxy. The broad-area transparency current density is 140 A-cm/sup -2/, the internal efficiency is 0.83, the waveguide loss is 5 cm/sup -1/. and T/sub 0/ = 62 K. Ridge waveguide laser diodes have a room temperature threshold of 8 mA and an efficiency of 0.32 mW/mA. >

Self-aligned buried-heterostructure lasers grown entirely by metalorganic vapor phase epitaxy

The effects of n-type dopant on InP embedding regrowth by metalorganic vapor phase epitaxy (MOVPE) are studied. It is found that the growth of the n-InP layer on the mesa structure is completely suppressed under a Se concentration of more than 8×1018 cm−3 and a mesa structure having a width of 1.1 μm. Using this novel MOVPE technique, a buried heterostructure laser diode is successfully fabricated without a selective growth mask. This achieves a threshold current as low as 14 mA, an external differential efficiency of 0.18 W/A, and an output power of more than 15 mW, at 25 °C.

Thin upper-confining layer AlxGa1−xAs-GaAs quantum well heterostructure laser diodes

AlxGa1−xAs-GaAs quantum well heterostructure (QWH) laser diodes with much thinner upper confining layers (0.6, 0.45, 0.3, and 0.2 μm) than usual (1–2 μm) are demonstrated. The diodes exhibit well behaved transverse far-field patterns, low broad-area pulsed threshold current densities, and high differential quantum efficiencies. The diodes with thinnest upper confining layers, ∼0.2 μm, have broad-area pulsed threshold current densities as low as Jth∼169 A/cm2 and a total external differential quantum efficiency ηT∼53% (∼500 μm long cavities). Stripe-geometry (40 μm wide) laser diodes made from the crystals with 0.2 μm upper confining layers exhibit room-temperature continuous (cw) threshold currents of 60 mA, output powers of ∼200 mW/facet (uncoated), and transverse far-field patterns with a full angle half power (FAHP) of 48°. Nonoptimized narrow-stripe (∼4 μm) native-oxide index-guided laser diodes fabricated on the same 0.2 μm confining layer QWH crystal operate at pulsed thresholds as low as 9 mA and continuous thresholds of 16 mA, with total external differential quantum efficiencies of 39% pulsed and 30% cw.

Cross-sectional transmission electron microscopy parallel to the active stripe of degraded buried heterostructure distributed feedback laser devices

We demonstrate for the first time that cross-sectional transmission electron microscopy can be applied parallel to the active stripe of a distributed feedback buried heterostructure laser diode to identify the cause for degradation during reliability qualification. A dominant defect mechanism is found to be the generation of dislocation loops at or near the grating/waveguide-layer interface which subsequently propagate up through the multilayer structure. The vertical segments of the loops tend to be trapped onto the {111} planes to form a V-shaped configuration as revealed in the (011) cross section. A dislocation reaction mechanism is proposed to explain the observed dislocation configuration. Furthermore, complicated dislocation loops are grown out of the segments of dislocation threading through the active region forming &amp;lt;100≳ dark line defects revealed by the electroluminescence. The defect growth mechanism is believed to be a condensation of point defects induced by the nonradiative recombination assisted point defect migration process similar to that previously observed in degraded channeled substrate buried heterostructure lasers. The nucleation of dislocations at or near the grating/waveguide layer interface is consistent with a high interfacial strain observed in the degraded devices.