Separate Confinement Heterostructure Laser Diodes Research Articles

Graded Cladding Layers in Infrared III-Arsenide Separate Confinement Heterostructure Laser Diodes

Graded aluminum composition in AlGaAs n-cladding and p-cladding layers have been shown to exhibit improved optoelectronic performance in the single quantum well separate confinement heterostructure laser diode (SQW SCH LD) in the infrared region. The output power of the laser diode is increased up to 45 mW by using graded aluminum composition in n-/p- cladding layers. In addition, the lasing threshold current density is also lowered which results in a significant optical gain. The stimulated emission rate also improves due to improved electron-hole recombination and, thus, resulting in improved lasing.

Performance and reliability improvement of 905 nm high power laser diode by design, fabrication and characterization of high damage threshold mirrors

The performance improvement of 905 nm InGaAs/AlGaAs/GaAs Single Quantum Well Separate-Confinement Heterostructure Laser Diode (SQW-SCH-LD) in consequence of three-step procedure for facet passivation and protection was demonstrated. Initially, processed InGaAs/AlGaAs/GaAs SQW-SCH LD wafer was scribed and cleaved in ambient atmosphere. Secondly, the air-exposed bar facets were cleaned and impurities were removed with Ar + irradiation and bombardment. Finally, after simulation, mirrors consist of single-layer Al2O3 as Low-Reflection (LR) and multilayer |(Al2O3/Si)4| as High-Reflection (HR) coatings were deposited on front and back facets, respectively. Mirror's surface and interface properties were investigated by UV-Vis-NIR Spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Burn-in test, Life-time test and Thermography. Spectrophotometer results of coated mirrors were in appropriate adaptation with the simulation results. High magnification FESEM images reveal the precise repeatability stacked Al2O3/Si 8-layers with amorphous structure on GaAs substrate. Thermographic image of front facet after life-time reveals that front mirror retains initial quality. In the case of coated front mirror and in Continues-Wave laser mode, laser induce damage threshold (LIDT) improved and increased up to >> 45.75 kW/cm2. Improvement in mirror coating process results in enhancement laser reliability and operational parameters such as increasing output power and power efficiency, decreasing degradation rate without any catastrophic optical mirror damage.

Properties of InGaN blue laser diodes grown on bulk GaN substrates

High-pressure growth from solution is at present the only method able to provide true bulk GaN monocrystals. In this paper, we would like to demonstrate that in spite of their small, centimeter range size, they can become a technological platform for the realization of high-quality violet and near-UV laser diodes. We used MOVPE technique to deposit InGaN/AlGaN/GaN layers forming a separate confinement heterostructure laser diode. These devices are characterized by a low density of dislocations (∼10 5 cm −2) and a high optical output power of 1.9 W, measured in short pulses (30 ns) to prevent the structure from overheating. We will briefly discuss the challenges we face during the process of optimization of these devices.

Growth and in situ annealing conditions for long-wavelength (Ga, In)(N, As)/GaAs lasers

The conjugated effect of growth temperature and in situ thermal annealing on the photoluminescence properties of In0.4Ga0.6As0.985N0.015/GaAs quantum wells (QWs) grown by molecular-beam epitaxy has been investigated. The interplay between growth temperature and annealing effects is such as the optimum growth temperature is not the same for as-grown and annealed samples. By using the combination of a low growth temperature and a high in situ annealing temperature, separate confinement heterostructure laser diodes with a single In0.4Ga0.6As1−xNx (x=0.015–0.021)/GaAs QW have been grown. The broad area devices emit from 1.34 to 1.44 μm at room temperature with a threshold current density of 1500–1755A∕cm2.

Study on InGaAsP–InGaAs MQW-LD With Symmetric and Asymmetric Separate Confinement Heterostructure

We studied symmetric and asymmetric InGaAsP-InGaAs 1.55-/spl mu/m multiquantum-well (MQW) laser diodes (LDs) with highly p-doped layers in the two-step separate confinement heterostructure (SCH). The p-doping in p-SCH suppresses the electron overflow from the MQWs to p-SCH, but it is an origin of free carrier absorption loss. An additional InGaAsP layer inserted inside n-SCH makes asymmetric field distribution and, therefore, reduces the portion of optical field distribution in highly p-doped regions with high optical loss. Compared with symmetric structure, asymmetric SCH LD has low threshold current density, low internal loss, and high and flat slope efficiency with respect to temperature.

Operation and Catastrophic Optical Degradation of II-VI Laser Diodes at Output Powers larger than 1 W

An output power of 1.55 W, the highest ever reported, at 20 °C has been achieved for a ZnCdSSe/ZnSSe/ZnMgSSe separate-confinement heterostructure laser diode under short-pulsed operation. A differential quantum efficiency of 28% and a maximum conversion efficiency of 1.5% were obtained. The output power was limited by catastrophic optical damage (COD) of the facets, as proved by atomic force microscopy (AFM).

Analysis of facet reflectivity of InGaAsP separate confinement heterostructure (SCH) laser diodes

Variations of the cleaved facet reflectivity, mirror loss, and optical confinement factor of a separate confinement heterostructure (SCH) laser diode have been investigated. The analysis that is based on the effective refractive index method has been carried out for both fundamental TE and TM modes at a 1.55 μm wavelength. Analytical expressions are given for these parameters in terms of the refractive indexes and thicknesses of various SCH laser diode layers. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 196–202, 2000.

High Power InGaN Violet Laser Diode.

A violet InGaN multi-quantum-well (MQW) separate confinement-heterostructure laser diode was grown on epitaxially laterally overgrown GaN (ELOG) on sapphire. The LDs showed an output power as highas 30 mW under room-temperature continuous-wave (CW) operation. The estimated lifetimes of the LDs were more than 1000 hours, during constant 30 mW output power at a case temperature of 60°C

Significant progress in II-VI blue-green laser diode lifetime

A II-VI laser diode lifetime of > 140 h at 40°C, as well as ~400 h at 20°C, has been achieved for a ZnCdSe/ZnSSe/ZnMgSSe separate-confinement heterostructure laser diode under continuous-wave operation with a constant output power of 1 mW. Progress has been made towards increasing the basic reliability of ZnMgSSe-based wide bandgap laser diodes by reducing point defects.

Heterointerface control of ZnSe based II–VI laser diodes

The density of pre-existing crystal defects such as stacking faults is reduced less than 3 × 10 3 cm −2 when there is a GaAs buffer layer and when a GaAs layer is irradiated with Zn flux prior to ZnSe growth. This progress in controlling a GaAs/ZnSe heterointerface has made possible a ZnCdSe/ZnSSe/ZnMgSSe separate-confinement heterostructure laser diode with a lifetime of over 100 h at room temperature under CW conditions. We believe that we have entered into a stage where the operation of II–VI laser diodes is limited by recombination-enhanced defect reactions. We have observed surface roughening in ZnSe layers, as well as in ZnSSe and ZnMgSSe layers, all grown under II-rich conditions. The compositional modulation in ZnMgSSe is indicated to be caused by corrugations on the surface, but not by the instability of the material.

Solid source MBE growth and regrowth of 1.55 μm wavelength ridge lasers

Abstract We report on the solid source molecular beam epitaxial growth of Ga x In (1 − x ) As y P (1 − y ) and its application to separate confinement heterostructure laser diodes operating at 1.55 μm. High-quality quaternary films were grown reproducibly with a band gap wavelength of 1.3 μm. Separate confinement heterostructure laser diodes operating at 1.55 μm were produced with active regions containing four Ga 0.47 In 0.53 As, Ga 0.27 In 0.73 As 0.8 P 0.2 , or InAs 0.6 P 0.4 quantum wells. Broad area laser threshold current densities were as low as 275 A/cm 2 and equal the best results reported for similar devices grown by other techniques. Ridge lasers were fabricated with threshold currents of 20 mA and external quantum efficiencies of 0.21 mW/mA per facet. Specular InP was regrown over etched ridges and was used to produce buried ridge laser diodes.

Room-temperature continuous-wave operation of ZnSe-based blue-green laser diode grown by molecular beam epitaxy

ZnSe-based II-VI laser diodes were grown by using molecular beam epitaxy (MBE) on GaAs(1 0 0) substrates. Continuous-wave, stimulated emission at room temperature was observed at a wavelength of 536.5 nm with a threshold current of 45 mA (642 A/cm 2 ) from a ZnCdSe/ZnSSe/ZnMgSSe single quantum well separate confinement heterostructure laser diode. A lifetime of 11 s was achieved when the defect density of laser diode structure was less than 10 5 cm -2 . Electroluminescence tests were conducted to find the origin of the defect generation at the laser diode structure. We monitored the generation of the dark line defects along during the electroluminescence.

First III–V-nitride-based violet laser diodes

InGaN multi-quantum-well (MQW) structure laser diodes (LDs) were grown by metalorganic chemical vapor deposition on a sapphire substrate with (112̄0) orientation (A face). The mirror facet for a laser cavity was formed by cleaving the substrate along the (11̄02) orientation (R-face). The structure of the LDs was an InGaN MQW/GaN/AlGaN separate confinement heterostructure (SCH). As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs showed strong stimulated emission at a wavelength of 415.3 nm under pulsed current injection above 360 mA at room temperature. The laser threshold current density was 6 kA/cm2. As a maximum characteristic temperature of the threshold current, T0 = 313 K was obtained for the InGaN MQW/GaN/AlGaN SCH LDs.

Room temperature laser operation of wide band-gap II–VI laser diodes.

A lifetime of over 100 h has been achieved at room temperature under CW conditions for a ZnCdSe/ZnSSe/ZnMgSSe separate-confinement heterostructure laser diode with a dark-spot density lower than 3 × 10 3 cm −2. The density of pre-existing crystal defects such as stacking faults is reduced when there is a GaAs buffer layer on the GaAs substrate and Zn is irradiated before ZnSe growth. We have entered into a stage where the operation of II–VI laser diodes is limited by recombination enhanced defect reaction. Despite possible rapid degradation mechanisms, especially those related to II–VI materials' higher ionicity than that of III–V material's, II–VI laser diodes have shown a lifetime of more than 100 h for the first time.

Solid source molecular beam epitaxy of low threshold 1.55 μm wavelength GaInAs/GaInAsP/InP semiconductor lasers

We report the growth and characterization of 1.55 μm wavelength GaInAsP based semiconductor lasers grown by solid source molecular beam epitaxy. Quaternary compositions were reproducible over time. Photoluminescence and x-ray diffraction spectra indicate abrupt quantum well interfaces. Separate confinement heterostructure laser diodes with four quantum wells had threshold current densities as low as 580 A/cm2 and 275 A/cm2 for unstrained Ga0.47In0.53As and strained Ga0.27In0.73As0.8P0.2 wells, respectively. These results are as good as the best results reported for similar lasers grown by any growth technique.

Room-temperature continuous-wave operation of blue-green CdZnSSe/ZnSSe quantum well laser diodes

Room temperature continuous wave operation of CdZnSSe/ZnSSe quantum well laser diodes based on wide-gap II-VI semiconductors with lifetimes >3 h has been demonstrated. The density of stacking faults and threading dislocations present inside the laser diodes is /spl sim/5/spl times/10/sup 4//cm/sup 2/. Laser emission was observed at a wavelength of /spl sim/529 nm with a threshold current density of /spl sim/460 A/cm/sup 2/ and a threshold voltage of /spl sim/5 V in index-guided CdZnSSe/ZnSSe/MgZnSSe separate-confinement heterostructure laser diodes.

100 h II-VI blue-green laser diode

By reducing the dark-spot density to <3 × 103 cm-2, device lifetime exceeding 100 h has been obtained for a ZnCdSe/ZnSSe/ZnMgSSe single quantum well separate-confinement heterostructure laser diode (LD) under room temperature continuous-wave operation with a constant light output power of 1 mW. The threshold current density is 533 A/cm2 and the lasing wavelength is 514.7 nm. Considering the dark-spot density, we have concluded that the failure of this LD is not caused by degradation from macroscopic defects such as stacking faults, but by recombination enhanced defect reaction.

Molecular beam epitaxy growth and characterizations of (Zn, Mg)(S,Se) epilayers for II–VI blue/green laser diodes

We report room temperature (pulsed) lasing at 463 nm from a (Zn,Mg)(S,Se) separate confinement heterostructure laser diode. Two issues related to the development of even bluer II–VI laser diodes, namely, the ‘‘AX center’’ and compositional modulation, as suggested from electrical and microstructural characterizations of the blue laser diode, respectively, will be identified.

On degradation of ZnSe-based blue-green diode lasers

The degradation mechanism of ZnMgSSe/ZnSSe/ZnCdSe separate confinement heterostructure laser diodes is studied under continuous wave and pulsed operation at room temperature. The degradation of the active quantum well is caused by formation of optically inactive areas which nucleate at paired stacking faults. These ‘‘dark defects’’ are identified as areas of dislocation network and point defect segregation.

Issues of II–VI molecular-beam epitaxy growth toward a long lifetime blue/green laser diode

Although many advances in the field of II–VI laser diodes have been reported since the first demonstrations of II–VI lasers in the summer of 1991, several obstacles still exist along the path towards long-lived II–VI laser diodes. This article will discuss mechanisms which lead to the degradation of the pseudomorphic separate confinement heterostructure laser diodes. Point defects and stacking faults are shown to play an important role in the degradation of these laser diode structures. The importance of controlling the substrate temperature to control the strain will be shown; a method to improve substrate temperature control will be provided.