Quantum-well Laser Structures Research Articles

Temperature sensitivity of InGaAs quantum-dot lasers grown by MOCVD

Temperature-dependent cavity length studies have been performed on multiple stack strain compensated InGaAs quantum-dot (QD) active region broad stripe laser structures grown by metal-organic chemical vapor deposition. The characteristic temperature coefficients of the threshold current density (T/sub 0/) and external differential quantum efficiency (T/sub 1/) were calculated from variable temperature measurements. The correlation of the T/sub 0/,T/sub 1/ values and the extracted values of the characteristic temperature coefficients of the transparency current density, material gain, injection efficiency, and internal loss (T/sub tr/,T/sub g0/,T/sub /spl eta/inj/,T/sub /spl alpha/i/) from the temperature-dependent study is discussed. The T/sub 1/ values are higher than 400 K for five-stack QD laser structures, comparable values to conventional quantum-well (QW) laser structures. T/sub 0/ values are lower than 100 K. Extracted material gain parameters are found to increase with increasing temperature for the three-stack QD structure, and are nearly temperature independent for the five-stack structure, different to that observed in InGaAs QW lasers.

Analysis of inductively coupled argon plasma-enhanced quantum-well intermixing process for multiple bandgap implementation

The inductively coupled argon (Ar) plasma-enhanced quantum-well intermixing has been investigated for the implementation of multiple bandgaps in an InGaAs/InGaAsP quantum-well laser structure. Multiple bandgap control is achieved by controlling the local defect concentrations without manipulating the critical rapid thermal annealing process using a multi-step plasma exposure or a spatial defect modulation. The interdiffusion process is found to obey Fick's law and enhanced by the near-surface point defects after a short plasma exposure time. For a prolonged exposure, the enhancement is reduced attributed to the possible formation of defect clusters. With single-step plasma exposure, the defect concentrations, thus intermixing degree, can be controlled using a variable window opening. This work demonstrates the practical approaches of multiple bandgap creation suitable for the photonic-integrated circuit application.

Ultraviolet lasing from optically pumped BeMgZnSe quantum-well laser structures

We achieved lasing of an optically pumped ultraviolet BeMgZnSe-based quantum-well laser grown closely lattice matched to a GaP substrate. A laser emission wavelength of 373 nm at 13 K was observed. The threshold excitation power density was 0.415MW∕cm2 at 13 K. In addition, we have demonstrated lasing up to 130 K. This indicates that the BeMgZnSe compound is promising as a new candidate for ultraviolet (UV) laser diodes, which possess potential application for UV optoelectronic integrated circuits UV-OEICs on silicon substrates.

Thermal excitation effects of photoluminescence of annealed GaInNAs∕GaAs quantum-well laser structures grown by plasma-assisted molecular-beam epitaxy

Ga In N As ∕ Ga As quantum well laser structures have been grown by plasma-assisted molecular beam epitaxy. Rapid thermal annealing was applied to suppress the nitrogen-related localized states in the material. These nitrogen-related localized states significantly quench the photoluminescence due to its low radiative recombination efficiency, compared to band-to-band transitions. Further, the thermal excitation processes of carriers from localized states to extended states result in the high temperature-sensitivity of light emission, which may lead to a low characteristic temperature if such structures are used in a laser diode. Our experiments have shown that annealing at 760°C for 120s is insufficient to totally eliminate the nitrogen-related localized states, which may require a higher temperature anneal process.

Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer

ABSTRACTWe report the intermixing enhancement using the Ge-doped sol-gel derived silica encapsulant layer in InGaAs/InGaAsP quantum-well laser structure. A bandgap shift of ∼64 nm has been observed from 16% Ge-doped silica capped sample at an annealing temperature of 630°C while the intermixing at the similar temperature can be effectively suppressed with the e-beam evaporated SiO2 encapsulant layer. Using our theoretical model, nearly identical activation energy of 1.7±0.5 eV was obtained from the intermixed sample with Ge-doped silica. Similar intermixing enhancement holds for high Ge-content cap in the intermixed GaAs/AlGaAs quantum-wells related to Ga vacancy injection. We postulate that the dissimilarity in interdiffusion behavior between 0% and 16% Ge-doped silica capped sample is only attributed to the difference in the number of beneficial vacancies that involve in the intermixing process.

Quantum well intermixing for the fabrication of InGaAsN/GaAs lasers with pulsed anodic oxidation

Quantum well (QW) intermixing was carried out by post-growth rapid thermal annealing in InGaAsN/GaAs QW laser structures grown by solid-source molecular-beam epitaxy. The intensity and width of the photoluminescence peak showed a dependence on annealing temperature and time, and the maximum intensity and minimum linewidth were obtained after the wafer was annealed at 670 °C for 60 s. The peak luminescence energy blueshifted with increasing annealing time, although it plateaued at an annealing time that corresponded to that yielding the maximum luminescence intensity. The diffusion coefficient for indium was determined from a comparison between experimental data and modeling, but showed that QW intermixing alone was not sufficient to account for the relatively large blueshift after annealing. Defects related to the incorporation of nitrogen in the QW layer were responsible for the low photoluminescence efficiency in the as-grown samples and were annealed out during rapid thermal annealing. During annealing, nitrogen interstitials moved to vacancy sites within the QW and thus suppressed QW intermixing. After annealing wafers under conditions giving the maximum luminescence intensity, lasers were fabricated with pulsed anodic oxidation.

Improved photoluminescence of InGaAsN–(In)GaAsP quantum well by organometallic vapor phase epitaxy using growth pause annealing

The metalorganic chemical vapor deposition of a highly strained InGaAsN quantum-well (QW) surrounded by (In)GaAsP direct barrier layers is investigated. We found that growth pause annealing with AsH3, performed immediately before and after the growth of the QW, significantly improves the optical quality of InGaAsN QW with (In)GaAsP direct barriers. The utilization of larger band gap barrier materials, such as InGaAsP or GaAsP, will potentially lead to reduced carrier leakage from the QW laser structures.

Si doping for n- and p-type conduction in AlxGa1−x As grown on GaAs(311)A by molecular-beam epitaxy

For Si-doped AlxGa1−xAs(311)A with 0⩽x⩽1 grown by molecular-beam epitaxy, a systematic study of electrical properties is performed depending on growth conditions. A phase diagram for the conversion of the conduction type as a function of growth temperature and V/III beam-equivalent pressure ratio is established for AlxGa1−xAs layers. To achieve n-type conduction in AlxGa1−xAs layers, high arsenic flux and growth temperatures not exceeding about 550 °C are required, whereas low arsenic flux and higher growth temperatures lead to p-type conduction. For Si-doped AlxGa1−xAs(311)A layers with x>0.5, p-type conduction is reported with a Si doping efficiency above 90%. Based on these results, all-Si-doped strained-layer In0.2Ga0.8 As/GaAs(311)A quantum-well laser structures with x=0.5 and 0.8 in the cladding layers were grown. Compared with reference laser structures grown on GaAs(100) and doped with Be, a better lasing performance of the all-Si-doped (311)A-oriented single quantum-well laser structures is obtained. For 1.5 mm long conventional broad area lasers, we achieve a lower threshold current density (280 A/cm2), an internal quantum efficiency of about 85%, and an internal optical loss of 9 cm−1.

Enhanced optical and structural properties of strain-compensated 1.3-μm GaInNAs/GaNAs/GaAs quantum-well structures by insertion of strain-mediating layers

We report on luminescence and structural properties of strain-compensated 1.3-μm GaInNAs/GaNAs/GaAs quantum-well (QW) laser structure, grown by solid-source molecular beam epitaxy with an rf-coupled nitrogen plasma source. The layer design consists of a strain-mediating GaInNAs layer sandwiched in between a highly compressive GaInNAs QW and a strain-compensating GaNAs layer. Insertion of the strain-mediating layer shifts light emission towards longer wavelengths, increases light emission, and improves structural properties of the QW, as deduced from the measurements of photoluminescence and X-ray diffraction.

Monolithic multiple wavelength ridge waveguide laser array fabricated by Nd:YAG laser-induced quantum well intermixing

Maskless selective area cw Nd:YAG laser annealing of GaInAsP/InP quantum well (QW) structures has been investigated as a possible route towards the fabrication of monolithically integrated photonic circuits. Laser irradiation of a 5 QW laser structure, originally designed for lasers emitting at 1.52 μm, yielded material having a continuously changing band gap ranging from 1.52 to 1.4 μm over the distance of about 3 mm. Bars with arrays of ridge waveguide lasers, having cavity lengths from 300 to 600 μm, were fabricated from the processed material. An individual bar, 2–3 mm long, comprised lasers operating typically between 1.4 and 1.52 μm. The lasers showed stable threshold current density and high quantum efficiency at all operating wavelengths. The results indicate that the applied approach has the potential to realize the cost-effective fabrication of advanced photonic devices and photonic integrated circuits.

Band-edge aligned quaternary carrier barriers in InGaAs-AlGaAs high-power diode lasers for improved high-temperature operation

A new type of band-edge aligned carrier barrier is introduced into InGaAs-AlGaAs single quantum-well (SQW) high-power diode laser structures in order to prevent thermionic emission and the overflow of carriers at elevated operating temperatures. These barriers, which are located in the direct vicinity of the active zone of the laser, are undoped to avoid free-carrier absorption. An InGaAs-AlGaAs SQW laser structure with a 10-nm-thick AlGaAsSb electron-blocking layer on the p-side of an In/sub 0.2/Ga/sub 0.8/As quantum well was realized. The composition of this layer was adjusted so that its valence-band edge matches that of the adjacent AlGaAs waveguide layer. This is to prevent any additional voltage drop or series resistance due to the injection of holes into the quantum well through the electron blocking layer. These lasers show a high characteristic temperature T/sub 0/ of about 225 K for 1500-/spl mu/m-long as-cleaved devices, which is about 60 K higher than the same laser structure without the blocking layer. Simultaneously low internal losses (/spl alpha//sub i//spl ap/1.5 cm/sup -1/ at 20/spl deg/C) and high internal quantum efficiencies (/spl eta//sub i//spl ap/93% at 20/spl deg/C) are achieved. No additional voltage drop or series resistance was measured. The higher temperature stability is mainly attributed to the suppression of carrier leakage and a reduced free-carrier absorption at elevated temperatures.

Small-signal impedance characteristics of quantum-well laser structures

Small-signal impedance characteristics of quantum-well laser structures are analyzed. A simple analytical expression for the frequency dependence of below-threshold small-signal impedance is derived and verified experimentally. It is shown that the differential carrier lifetime and quantum-well transport and capture times can be extracted from electrical impedance measurements.

The effects of InP grown by He-plasma assisted epitaxy on quantum-well intermixing

He-plasma assisted InP (He*-InP) layers grown by gas source molecular beam epitaxy (GSMBE) have been employed to enhance quantum well (QW) intermixing induced by rapid thermal annealing in a 1.5 /spl mu/m InGaAsP QW laser structure. Inserting a 40 nm He*-InP layer just above the active region enhances the blue-shift for anneal temperatures larger than 680/spl deg/C, and a 42 nm additional blue-shift is obtained at 750/spl deg/C for samples with the He*InP layer, compared to samples with normal InP replacing the He*-InP. This is accompanied by a reduction in the photoluminescence (PL) intensity for anneal temperatures greater than 600/spl deg/C and is attributed to the migration of nonradiative defects from the He*-InP layer into the QWs. Insertion of a thin InGaAs layer between the He*-InP layer and the QW blocks the diffusion of these nonradiative defects into the QW. The results indicate that the He*-InP material could prove useful in QW intermixing to achieve integrated optoelectronic devices, in particular for high-frequency devices which require short carrier lifetimes.

Room-temperature operation of GaInAsN-GaAs laser diodes in the 1.5-μm range

GaInAsN-GaAs double quantum-well (DQW) laser structures emitting in the 1.5-/spl mu/m range were grown by solid source molecular beam epitaxy using a radio frequency plasma source for nitrogen activation. Lasing operation in the 1.5-/spl mu/m wavelength region has been realized for fabricated ridge waveguide laser diodes (LDs) under pulsed condition up to record high temperatures of 80/spl deg/C resulting in an emission wavelength of 1540 nm. This is the highest emission wavelength for laser diode operation based on GaAs. In addition, to investigate the optical properties of the active region, photoluminescence studies of underlying GaInAsN-GaAs QW structures emitting at wavelengths up to 1.55 /spl mu/m are presented.

Gain, refractive index change, and linewidth enhancement factor in broad-area GaAs and InGaAs quantum-well lasers

We report experimental and theoretical results for the injection-level dependence of the gain, refractive index variation, and linewidth enhancement factor (/spl alpha/) for four different quantum-well (QW) laser structures. Two of the lasers have GaAs QW layers that vary in width while the other two have InGaAs active layers that vary in QW depth. Experimental Hakki-Paoli data are used to compare gain, index change, and /spl alpha/-parameter between these pairs of devices. The results of two simulations are compared to the experimental data. The first is based on the approximation of parabolic bands for both the conduction and valence bands while the second employs the k/spl middot/p method to refine the calculation of the valence bands. Our findings include: (1) narrower and deeper QWs yield lower /spl alpha/ values; (2) modeling results from the k/spl middot/p method are only slightly improved over those from the parabolic band model; (3) at high injection levels, stimulated emission below threshold is a prominent effect in these devices; and (4) at high injection levels, carriers in the barrier energy states above the well are shown to be responsible for increasing /spl alpha/ values.

High-performance strain-compensated InGaAs-GaAsP-GaAs (/spl lambda/=1.17 μm) quantum well diode lasers

This letter reports studies on highly strained and strain-compensated InGaAs quantum-well (QW) active diode lasers on GaAs substrates, fabricated by low-temperature (550/spl deg/C) metal-organic chemical vapor deposition (MOCVD) growth. Strain compensation of the (compressively strained) InGaAs QW is investigated by using either InGaP (tensile-strained) cladding layer or GaAsP (tensile-strained) barrier layers. High-performance /spl lambda/=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 1500-μm-cavity devices and transparency current densities of 50 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The use of GaAsP-barrier layers are also shown to significantly improve the internal quantum efficiency of the highly strained InGaAs-active laser structure. As a result, external differential quantum efficiencies of 56% are achieved for 500-μm-cavity length diode lasers.

Carrier and light trapping in graded quantum-well laser structures

We investigated the carrier and light trapping in GaInAs/AlGaAs single-quantum-well laser structures by means of time-resolved photoluminescence and Raman spectroscopy. The influence of the shape and depth of the confinement potential and of the cavity geometry was studied by using different AlGaAs/GaAs short-period superlattices as barriers. Our results show that grading the optical cavity improves considerably both carrier and light trapping in the quantum well, and that the trapping efficiency is enhanced by increasing the graded confining potential.

InAs/InAs(P,Sb) quantum-well laser structure for the midwavelength infrared region

Strained InAs1−xSbx(0&lt;x&lt;0.22) quantum wells with InAs, InAsP, or InAsPSb barrier layers have been grown by metal–organic vapour-phase deposition on InAs substrates. Their photoluminescence and electroluminescence were studied at 20 K. The photoluminescence peak-wavelength evolution with the antimony composition x and the nature of the barrier were theoretically predicted in a satisfactory manner under the assumption of a type-II band alignment for the InAsSb/InAs system with a valence band ratio Qv=−1.30. This hypothesis leads to a type-IIa band alignment for the arsenic-rich InAsSb/InAsP system. Starting from this result, a `W&apos; laser structure, consisting of ten periods of InAsSb/InAsP/InAsSb/InAsPSb multiquantum wells in the active region, a broadened InAsPSb waveguide, and AlAsSb cladding layers, is proposed for room-temperature emission near 3.3 μm.

Control of surface states in GaSb/AlxGa1−xAsySb1−y/GaxIn1−xSb/AlxGa1−xAsySb1−y quantum well structures

GaSb-based lasers show advanced capabilities over other material for the far-infrared wavelength range. However, for quantum-well (QW) laser structures of AlxGa1−xAsySb1−y/GaxIn1−xAsySb1−y/AlxGa1−xAsySb1−y grown on GaSb, each component element etches at a different rate, making it difficult to achieve quality surfaces sufficiently free of defects. Thus, in this letter, the effects on the surface quality of GaSb-based laser materials have been studied using phosphoric acid etching, boron trichloride reactive ion etching (RIE), and a postetch sulfur treatment. In addition, the quality of the surface is compared for two barriers of AlAs0.07Sb0.93 and Al0.9Ga0.1As0.07Sb0.93, based on current–voltage measurements as a function of temperature. The best surfaces were produced by RIE and by using as much Ga in the barriers as the device operation allows. A generation center in the Ga0.81In0.19As0.12Sb0.88 was found at 0.14 eV for QW diodes with low surface conduction.

Very closely spaced quadspot native-oxide confined 780-nm semiconductor lasers

We describe the fabrication and characteristics of 7-/spl mu/m spaced quadspot, independently addressable 785-nm native-oxide confined ridge waveguide laser diodes. The devices are fabricated from an Al/sub 0.1/Ga/sub 0.9/As-Al/sub 0.4/Ga/sub 0.6/As-Al/sub 0.5/In/sub 0.5/P quantum-well separate confinement heterostructure laser structure. Wet oxidation of the p-Al/sub 0.5/In/sub 0.5/P cladding layer is used to form a native oxide for not only ridge waveguide confinement, but also electrical insulation to allow electrical connection to laser stripes. These diodes show excellent performance: uniform threshold currents below 8 mA and differential quantum efficiencies over 35%/facet. The diodes show crosstalk less than 5%.