High-power highly strained InGaAs quantum-well lasers operating at1.2 μm

High-power highly strained In_xGa_1-xAs quantum-well lasers operating at 1.2 μm are demonstrated. The edge emitting broad area (BA) laser diode structures are grown by metal organic vapor phase epitaxy at low growth temperatures using trimethylgallium, trimethylindium, and arsine sources. In the laser structure, an InGaAs QW is sandwiched between the GaAs waveguide and AlGaAs cladding layers. The operating wavelength for the laser diode at room temperature (20°C) is about 1206 nm, which redshifts to 1219 nm at 46°C. The transparency current density for the BA laser diodes is as low as 52 A/cm² and the characteristic temperature value is 76 K. High-power laser operation in the pulse mode (about 1.6 W) at room temperature was achieved     

Relaxation study of AlGaAs cladding layers in InGaAs/GaAs (111)B lasers designed for 1.0-1.1 μm operation

InGaAs/GaAs-based lasers require thick AlGaAs cladding layers to provide optical confinement. Although the lattice mismatch between GaAs and AlGaAs is very low, relaxation may occur due to the thickness requirement for an AlGaAs waveguide of the order of microns. We have studied the relaxation of InGaAs/GaAs lasers with AlGaAs waveguides grown on GaAs (111)B substrates. We have observed by transmission electron microscopy (TEM) that certain AlGaAs layers show a high density of threading dislocations (TDs), whilst other AlGaAs layers remain essentially dislocation free. To explain the experimental results a model based on dislocation multiplication has been developed. TDs in the AlGaAs cladding layers are observed when the critical layer thickness (CLT) for dislocation multiplication has been overcome. Consequently, a design rule based on a modified CLT model for AlGaAs/GaAs (111)B is proposed.     

In-situ monitoring and control for MOCVD growth of AlGaAs and InGaAs

We have used spectroscopic ellipsometry to perform real-time monitoring during metalorganic chemical vapor deposition growth of AlGaAs (on GaAs) and InGaAs (on GaAs and InP). Optical constants for these materials were obtained up to growth temperatures of 600 to 700°C. This information permits real-time extraction of composition and layer thickness from the raw ellipsometric data at sample rates on the order of 0.5 Hz. We describe closed-loop control of composition and total layer thickness on AlGaAs-based structures, including Bragg reflectors. In-situ data obtained on double-heterostructure quantum-well laser structures demonstrate that spectroscopic ellipsometry is an extremely powerful monitoring and quality-control tool, giving important real-time information on complex structures that would be difficult and time-consuming to obtain after growth.     

High-performance strain-compensated InGaAs-GaAsP-GaAs(λ=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°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 λ=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm² for 1500-μm-cavity devices and transparency current densities of 50 A/cm². 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     

High temperature, high power InGaAs/GaAs quantum-well lasers withlattice-matched InGaP cladding layers

The authors report the high-temperature and high-power operation of strained-layer InGaAs/GaAs quantum well lasers with lattice-matched InGaP cladding layers grown by gas-source molecular beam epitaxy. Self-aligned ridge waveguide lasers of 3-μm width were fabricated. These lasers have low threshold currents (7 mA for 250-μm-long cavity and 12 mA for 500-μm-long cavity), high external quantum efficiencies (0.9 mW/mA), and high peak powers (160 mW for 3-μm-wide lasers and 285 mW for 5-μm-wide laser) at room temperature under continuous wave (CW) conditions. The CW operating temperature of 185°C is the highest ever reported for InGaAs/GaAs/InGaP quantum well lasers, and is comparable to the best result (200°C) reported for InGaAs/GaAs/AlGaAs lasers     

The effect of spacer-layer growth temperature on mobility in a two-dimensional electron gas in PHEMT structures

The effect of growth temperature of the AlGaAs spacer layer on mobility in a two-dimensional electron gas μ _e in single-side δ-doped pseudomorphic AlGaAs/InGaAs/GaAs transistor structures with a high electron mobility is studied experimentally. The energy-band diagram is analyzed using a self-consistent calculation. In order to study the electronic transport properties, an optimized structure in which there is no parallel conduction over the doped layer was chosen. It is shown that, in optimized structures, the mobility μ _e increases by 53% at T = 300 K and by 69% at T = 77 K as the growth temperature increases from 590 to 610°C, with the other parameters and the growth conditions remaining the same. It is assumed that this behavior is related to an improvement in the structural quality of the AlGaAs spacer layer and the AlGaAs/InGaAs/GaAs heteroboundary.     

A1.3 μm strained quantum well laser on a graded InGaAs buffer with a GaAs substrate

We grew a 1.3 μm strained-layer quantum well (SL-QW) laser with InGaP cladding layers on a lattice-relaxation buffer layer by metalorganic vapor phase epitaxy. For the lattice-relaxation buffer, we used a compositionally graded InGaAs/GaAs structure. The significantly reduced surface roughness of the InGaP cladding layers achieved by supplying a large amount of H₂Se enables CW operation of our 1.3 μm SL-QW laser. We achieved a low threshold current of less than 10 mA and a high characteristic temperature of 100K around room temperature.     

Low loss, thin p-clad 980-nm InGaAs semiconductor laser diodes with an asymmetric structure design

Thin p-clad InGaAs ridge waveguide quantum-well lasers having an asymmetric structure design were fabricated. The internal absorption coefficient is as low as 2.5 cm/sup -1/, due to the restricted field extension in the 0.3-/spl mu/m-thick p-type top AlGaAs cladding layer. Ti-Pt-Au metallization is used outside the ridge to provide adherence on the oxide while Au directly contacts the ridge region. It is shown that the most likely source of loss in these thin p-clad devices is scattering at the rough interface between Au and the p/sup ++/ top GaAs layer, after ohmic contact heat treatment.     

InGaAs tunnel-injection structures with nanobridges: Excitation transfer and luminescence kinetics

Methods of optical spectroscopy and electron microscopy have been used to study tunnel-injection nanostructures the active region of which consisted of an upper In_0.15Ga_0.85 As quantum-well layer and a lower layer of In_0.6Ga_0.4As quantum dots as a light emitter; both layers were separated by a GaAs barrier layer. Deviations from the semiclassical Wentzel-Kramers-Brillouin model are observed in the dependence of the tunneling time on barrier’s thickness. Reduction of the transfer time to several picoseconds at a barrier thickness smaller than 6 nm is accounted for by formation of InGaAs nanobridges between tops of quantum dots and the quantum-well layer; the nanobridges include those with their own hole state. The effect of an electric field induced by tunneling on the carriers’ transfer time in a tunnel-injection nanostructure is taken into account.     

InGaAs/GaAs应变量子阱激光器MOCVD生长研究

采用金属有机物化学气相淀积(MOCVD)方法生长了InGaAs/GaAs应变量子阱(QW),通过降低生长温度、提高生长速度以及采用应变缓冲层(SBL)结构,改善了应变QW生长表面质量和器件荧光(PL)谱特性,实验表明,通过优化工艺条件和采用SBL等手段提高了应变QW质量。生长的QW结构用于1054 nm激光器的制作,经测试,器件具有较低的阈值电流和较高的单面斜率效率,性能较好。     

AlGaAs-GaAs-InGaAs strained layer laser structure with performance independent of AlGaAs layer quality

An AlGaAs-GaAs-InGaAs strained layer laser structure has been shown to have a low threshold current density which is independent of AlGaAs layer quality. This threshold invariance is attributed to the use of a large GaAs region outside the InGaAs well to reduce the effects of traps in the AlGaAs on the active region of the laser and was demonstrated by characterising identical structures grown by molecular beam epitaxy (MBE) under different AlGaAs growth conditions. These results should have strong implications for the reliability and manufacturability of such lasers and for the integration with electronic devices where low temperature growth is required.<>     

Subthreshold current in MODFETs of tenth-micrometer gate

The subthreshold current of conventional GaAs/AlGaAs MODFETs and pseudomorphic InGaAs/AlGaAs MODFETs with the gate length down to 0.12 μm is investigated. The gate swing increases with the drain voltage and decreases with the gate length. It is attributed to charge injection from source to drain, limited by the channel potential barrier, which is a function of both the drain and the gate voltages. The pseudomorphic InGaAs/AlGaAs MODFETs show much better control than the conventional GaAs/AlGaAs MODFETs for the subthreshold current, especially with high drain biases. This shows that the pseudomorphic quantum-well structures can suppress the subthreshold current passing through the GaAs buffer region and reduce the undesirable short-channel effects     

A novel SAL-PINSCH quantum-well laser structure for a pinched beamdivergence

Summary form only given. An edge-emitting strained AlGaAs/InGaAs/GaAs quantum-well laser structure is reported. It has a periodic index separate confinement heterostructure (PINSCH) optical confinement layers for a small beam divergence and high output power. Preliminary measurements of AR/HR-coated self-aligned ridge waveguide lasers show a CW output power of up to 350 mW and a 20° transverse beam divergence at a 980-nm lasing wavelength. This low beam divergence results in a high coupling efficiency of 51% into single-mode fibers. The expanded optical field in PINSCH confinement layers significantly pinches the transverse beam divergence and increases the maximum output power     

Correlation between the reliability of laser diodes and the crystal perfection of epitaxial layers estimated by high-resolution x-ray diffractometry

The dependence of the degradation of high-power quantum-well GaAs/AlGaAs laser diodes, grown by molecular-beam epitaxy, on the crystal perfection of the individual layers of the heterostructure is investigated. The crystal perfection of the layers is estimated by highresolution x-ray spectrometry. A numerical fit of the diffraction-reflection curves is performed using the Debye-Waller static factor. It is shown that considerably higher crystal perfection of laser heterostructures can be obtained by using as the waveguide layers binary AlAs/GaAs superlattices instead of the solid solution AlGaAs. Fiz. Tekh. Poluprovodn. 33, 634–638 (May 1999)     

Optimization of the temperature mode of metal-organic chemical vapor deposition of the InAs(N) quantum dots on GaAs (001) with intense photoluminescence at 1.3 μm

The growth of the InAs(N) quantum dots on GaAs in a reduced-pressure reactor of metal-organic chemical vapor deposition (MOCVD) is studied. As the nitrogen source, dimethylhydrazine is used. It is currently well-known that the growth temperature of the InGaAs quantum dots should be limited in order to avoid undesirable In and Ga interdiffusion as well as reevaporation of In. However, thick GaAs barrier layers should be grown at the elevated temperature because of the pronounced effect of the growth temperature on the optical quality of the structure. An increase in the temperature of the substrate holder by 100°C requires interrupting the process in the MOCVD reactor for approximately 2 min. The time of this interruption for the temperature rise can come at various stages of the process, namely, (i) after growing the quantum dots and prior to growing the InGaAs coating layer, (ii) during the growth of the coating layer, (iii) after growing the coating layer and before growing the GaAs barrier layer, and (iv) during the growth of the GaAs barrier layer. It is shown that the last variant is the most appropriate for the structures with intense photoluminescence at 1.3 μm. In this case, the thin initial part of the barrier layer is grown under reduced temperature.     

MOCVD-grown InGaAs/GaAs/AlGaAs laser structures with a broad-area contact

A metal-organic chemical vapor deposition (MOCVD) technique is developed for a diode laser heterostructure in a system of InGaAs/GaAs/AlGaAs solid solutions; the optimal sizes and the doping profile of the structure are determined to minimize the internal optical losses. Mesa-strip diode lasers with a threshold density of current J _th=150–200 A/cm², internal optical loss factor α_i=1.6–1.9 cm^?1, and an internal quantum yield η_i=85–95% were fabricated. In the continuous lasing mode of a diode laser with a 100-µm-wide aperture and a wavelength of 0.98 µm, the optical power output was as high as 6.5 W and was limited by the catastrophic optical degradation of mirrors. The radiation divergence in the plane normal to the p-n junction amounts to θ_⊥. The use of wide-gap waveguide layers, which deepens the potential electron well in the active region, is shown to reduce the temperature sensitivity of the InGaAs/GaAs/AlGaAs laser heterostructures in the temperature range from 0 to 70°C.     

High-order diffraction gratings for high-power semiconductor lasers

A deep diffraction grating with a large period (∼2 μm) within one of the cladding layers is proposed for the implementation of selective feedback in a semiconductor laser. Frequency dependences of reflectance in the 12th diffraction order for rectangular, triangular, and trapezoidal diffraction gratings are calculated. It is shown that the maximum reflectance of the waveguide mode is attained using a rectangular or trapezoidal grating ∼2 μm deep in the laser structure. Deep trapezoidal diffraction gratings with large periods are fabricated in the Al_0.3Ga_0.7As cladding layer of a GaAs/AlGaAs laser structure using photolithography and reactive ion etching.     

量子阱平面光学各向异性的偏振差分反射谱研究

在室温下用偏振差分反射谱技术观察到了 Ga As/Al Ga As、In Ga As/Ga As和 In Ga As/In P三种量子阱材料的平面光学各向异性。我们发现 Ga As/Al Ga As量子阱 1 h→ 1 e跃迁的偏振度与阱宽成反比 ,与 In Ga As/In P量子阱的报道结果类似。 Ga原子偏析引起的界面不对称可以很好地解释这种行为。与之相反 ,In Ga As/Ga As量子阱的光学各向异性倾向于与阱宽成正比。目前还不能很好地解释这种现象。     

MOCVD-grown broad area InGaAs/GaAs/InGaP laser diodes

A MOCVD technology for growth of InGaAs/GaAs/InGaP laser heterostructures on a modified Epiquip VP-50-RP installation was developed. Mesa stripe laser diodes with threshold current density J _th=100–200 A/cm², internal optical loss α_i=1.3–1.7 cm^?1, and internal quantum efficiency η_i=60–70% have been fabricated. A CW output optical power of 5 W has been obtained for a single 100-µm-wide aperture mesa stripe laser diode emitting at 1.03 µm. It is shown that use of AlGaAs waveguide layers, which increase the conduction band barrier offset, lowers the temperature sensitivity of laser heterostructures within the temperature range 10–80°C.     

High-performance 980-nm quantum-well lasers using a hybrid materialsystem of an Al-free InGaAs-InGaAsP active region and AlGaAs claddinglayers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm² (at a cavity length of 1500 μm), internal quantum efficiency of ~95%, and low internal loss of 1.8 cm^-1. Both broad-area and ridge-waveguide laser devices are fabricated. For 100-μm-wide stripe lasers with a cavity length of 800 μm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T₀) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-μm-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A