Contribution of Auger recombination to saturation of the light-current characteristics in high-power laser diodes (λ = 1.0–1.9 m m)

Spectral and light-current characteristics of lasers based on the asymmetric separate-confinement heterostructures InGaAs/InGaAsAl/InP and InGaAs/GaAs/AlGaAs/GaAs were studied in the pulsed mode of lasing. It is shown that, at high levels of current pumping, the charge-carrier concentration in the active region of semiconductor lasers for the near-infrared optical region increases beyond the oscillation threshold; drastic saturation of the light-current characteristics is observed. Processes occurring in lasers as the charge-carrier concentration increases beyond the lasing threshold are studied theoretically. It is established that, at high pump levels, the rate of stimulated recombination decreases, the lifetime of charge carriers increases, and both the concentration of emitted photons and the quantum yield of stimulated radiation decrease. It is shown that variations in stimulated recombination, the decrease in the quantum efficiency, and saturation of the light-current characteristic in semiconductor lasers at high levels of current pumping are caused by the contribution of the nonradiative Auger recombination.     

Light-Emitting Diodes Based on an Asymmetrical InAs/InAsSb/InAsSbP Double Heterostructure for CO2 (λ = 4.3 μm) and CO (λ = 4.7 μm) Detection

Semiconductors - Asymmetrical double InAs/InAsSb/InAsSbP heterostructures are grown by metalorganic vapor phase epitaxy. Two types (A and B) of light-emitting diodes with wavelengths of 4.1 and 4.7...     

Module of Laser-Radiation (λ = 1064 nm) Photovoltaic Converters

Semiconductors - The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction...     

氧化铝基体3.7 μm与4.8 μm双波段带通滤光膜研制

以红外光学和薄膜技术为理论背景,详细介绍了氧化铝基体表面3.7 m与4.8 m双波段带通滤光膜的特性、制备及测试方法。氧化铝（Al2O3）由于其透光区域较宽,牢固度好,便于光学系统使用而被经常应用于中波红外光学系统中。采用软件优化计算和双面镀制截止带通滤光膜的方案,通过速率控制、离子辅助等工艺方法研制成功了可靠性和光谱特性皆优的双波段带通滤光薄膜。分析认为设计结构和优化算法对于薄膜通带平坦度、截止深度以及透过率有着明显的影响。制备工艺方面,除了合适的蒸发速率外,采取缓慢蒸发和弱离子能量辅助也是很重要的关键技术,最终光谱透过率测试平均大于87%,通过了环境测试,符合使用要求。     

High-power InAs/InAsSbP heterostructure leds for methane spectroscopy (λ ≈ 3.3 μm)

Two designs of light-emitting diodes (LEDs) based on InAsSbP/InAs/InAsSbP double hetero-structures grown by metal-organic vapor phase epitaxy on p− and n-InAs substrates have been studied. The current-voltage and electroluminescence characteristics of the LEDs are analyzed. It is shown that the LED design with a light-emitting crystal (chip) mounted with the epitaxial layer down on the LED case and emission extracted through the n-InAs substrate provides better heat removal. As a result, the spectral characteristics remain stable at increased injection currents and the quantum efficiency of radiative recombination is higher. The internal quantum efficiency of light-em itting structures with an emission wavelength λ = 3.3–3.4 μm is as high as 22.3%. The optical emission power of the LEDs is 140 μW at a current of 1 A in the quasi-continuous mode and reaches a value of 5.5 mW at a current of 9 A in the pulsed mode.     

Laser diodes with several emitting regions (λ = 800–1100 nm) on the basis of epitaxially integrated heterostructures

The results of a series of studies concerned with formation of epitaxially integrated InGaAs/AlGaAs and AlGaAs/AlGaAs heterostructures with several emitting regions and with investigation of properties of laser diodes based on the above structures operating in the spectral ranges λ = 800–810, 890–910, and 1040–1060 nm are summarized. It is shown that the suggested approach to integration of individual laser structures by the method of the MOVPE epitaxy operates efficiently in fabrication of laser diodes for a wide spectral range on the basis of various types of heterostructures. This approach made it possible to efficiently increase the output power of the laser diodes practically without variation in their mass-and-dimension characteristics. The main advantages of this approach and its limitations are outlined. Epitaxial integration of two laser heterostructures made it possible to increase the differential quantum efficiency by 1.7–2.0 times, while integration of three laser heterostructures increases the differential quantum efficiency by a factor of 2.5–3.0.     

Internal quantum efficiency of stimulated emission of (λ=1.55 µm) InGaAsP/InP laser diodes

The stimulated emission (η _i ^st ) of InGaAsP/InP separate-confinement double heterostructure lasers operating at λ=1.5–1.6 μm has been studied experimentally and theoretically. Laser heterostructures with a varied design of the waveguide layer were grown by MOCVD. The maximum internal quantum efficiency η _i ^st ≈97% was obtained in a structure with a double-step waveguide characterized by minimum leakage into the p-emitter above the generation threshold. The high value of η _i ^st is provided by low threshold and nonequilibrium carrier concentrations at the interface between the waveguide and p-emitter. The calculation yields η _i ^st values correlating well with the experimental data. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 2, 2003, pp. 243–248. Original Russian Text Copyright ? 2003 by Skrynnikov, Zegrya, Pikhtin, Slipchenko, Shamakhov, Tarasov.     

Optical Properties of Tellurium-Based Chalcogenide Alloys in the Far Infrared Region (λ > 30 μm)

Ternary telluride alloys of Ge–Se(Sb)–Te and Si–Ge(Ga)–Te systems are synthesized in glassy and crystalline states for use in the terahertz frequency range. The transmission spectra of the obtained alloys are measured and studied in a wide wavelength range from 0.75 to 300 μm. The possible mechanisms of their formation are discussed. A comparative analysis of the results shows that the Ge₁₄Sb₂₈Te₅₆ alloy of the GST system is most promising. Its phonon spectrum is in the range of 40–280 cm^–1, limiting the long-wavelength transmission window of this alloy by 35 μm. Optimization of the Ge₁₄Sb₂₈Te₅₆ composition, the removal of impurities, and heat treatment will promote a further decrease in the absorbance in the far-infrared spectrum of this alloy.     

1.3 μm InGaAsSb/GaAsSb量子阱激光器有源区结构设计

为了研制满足光纤通讯需求的高性能半导体激光器,对压应变InGaAsSb/GaAsSb量子阱激光器有源区进行了研究。根据应变量子阱能带理论、固体模型理论和克龙尼克-潘纳模型,确定了激射波长与量子阱材料组分及阱宽的关系。基于Lastip软件建立了条宽为50 μm、腔长为800 μm的半导体激光器仿真模型,模拟器件的输出特性,讨论了量子阱个数对器件光电特性的影响。结果表明：当量子阱组分为In0.44Ga0.56As0.92Sb0.08/GaAs0.92Sb0.08、阱宽为9 nm、量子阱个数为2时,器件的性能达到最佳,阈值电流为48 mA,斜率效率为0.76 W/A。     

Spectral characteristics of lasers based on InGaAsSb/InAsSbP double heterostructures (λ=3.0–3.6 µm)

It is shown that an increase in the internal losses beyond the lasing threshold in the lasers based on InGaAsSb/InAsSbP double heterostructures (wavelength range λ=3.0–3.6 µm, temperature T=77 K) causes the current-related shift of the laser mode to shorter wavelengths. This shift is as large as 80 cm^?1/A and can explain the broadening of the laser line from 5 to 7 MGz as the pump current increases.     

2 μm波段InGaAsSb/AlGaAsSb宽条多量子阱激光器

报道了用ＭＢＥ生长的ＩｎＧａＡｓＳｂ／ＡｌＧａＡｓＳｂ多量子阱材料做成的宽条激光二极管的性能。室温下以脉冲方式工作，实现了８３ｍＷ的峰值功率输出，阈值电流为２５０ｍＡ，典型峰值波长为２．００μｍ左右。     

1.8 μm波段台面条形结构InGaAsSb/AlGaAsSb量子阱激光器

报道了１．８μｍ波段台面第形结构ＩｎＧａＡｓＳｂ／ＡｌＧａＡｓＳｂ量子阱激光器的研制结果,器件在７７Ｋ下以脉冲方式工作,阈值电流约２５ｍＡ,中心波开约１．８４μｍ。     

3.7～4.8 μm中红外带通滤光膜研制

以光学薄膜理论为出发点,系统介绍了3.7～4.8 m带通滤光膜的理论设计与优化、实际生产制备以及成品测试方法。考虑到膜料性能及膜层匹配等问题,分别选用锗和一氧化硅作为高低折射率材料,并以氧化铝作为薄膜基底。确定了滤光膜的基础膜系,并使用Filmaster软件对膜系进行了设计和优化计算。在薄膜蒸镀过程中,根据材料选取合适的镀制工艺。通过温度控制、离子辅助等方法研制出了可靠性与光谱特性皆优的带通滤光膜,并对其光谱特性及膜层质量等进行了测试。根据设计目标修改工艺参数,最终确定可行的工艺流程,从而研制出了符合光学性能设计指标的3.7～4.8 m带通滤光膜。     

Modification of Photovoltaic Laser-Power (λ = 808 nm) Converters Grown by LPE

Laser-power converters for the wavelength λ = 808 nm are fabricated by liquid-phase epitaxy (LPE) on the basis of n-Al_0.07GaAs–p-Al_0.07GaAs–p-Al_0.25GaAs single-junction heterostructures. The converters are tested with uniform (pulse simulator) and partly nonuniform (laser beam) illumination distribution over the photoreceiving surface. In the former case, a monochromatic efficiency of η = 53.1% is achieved for samples with an area of S = 4 cm² at a power of 1.2 W. At S = 10.2 mm² the efficiency is 58.3% at a laser power of 0.7 W.     

Realization of triplet–triplet annihilation in planar heterojunction exciplex-based organic light-emitting diodes

Triplet–triplet annihilation (TTA) for enhancement of luminous efficiency occurs with difficulty in exciplex-based organic light-emitting devices (OLEDs) because it is an interaction among several neighboring donor and acceptor molecules. However, TTA has been realized in our planar-heterojunction (PHJ) exciplex-based OLEDs by using a thin recombination zone to enhance the interfacial density of the triplet states. The TTA process, which is characterized by a high-field decrease (HFD) in the magneto-electroluminescence from the PHJ OLEDs, appears at approximately 150 K and becomes stronger with decreasing temperature. At a given temperature, the higher the injected current is, the stronger HFD is observed. Additionally, we find that TTA could even happens at room temperature with appropriate selection of the donor molecule, which may be attributed to the favorable electron-donating ability of the methoxy group (–OCH₃) in the donor molecule and the matched overlaps of the intermolecular conformation of the donor and the acceptor.     

Long-Term Stability of a 640 × 512 InSb Focal Plane Array with a Pitch of 15 μm

The long-term stability of a 640x512 InSb focal plane array (FPA) with a pitch of 15 μm combined with a Stirling cooler and an interface block has been investigated.The dependences of the FPA correctability index on the operation time after a two-point correction of the irregularity have been obtained. The FPAs with two different circuits of the readout LSI cells that differ in the integration capacitance and transmission coefficients are considered. It has been found that, for the InSb FPA, the long-term stability is as high as several hours, which ensures continuous operation of the array in thermal imaging systems without additional calibrations.     

Enhanced device performance of quantum-dot light-emitting diodes via 2,2′-Bipyridyl ligand exchange

Quantum dots (QDs) are electroluminescent (EL) materials that have been developed as promising emitters in next-generation displays. The amount of charge carriers that travel to the light-emitting layer located at the interface between the hole- and electron-transport layers must be balanced in these displays to achieve maximum luminous efficiency. An existing amine ligand (oleylamine), which was coordinated on the surface of red-emitting InP/ZnSeS/ZnS QDs, was partially exchanged with two 2,2′-bipyridyl derivatives to enhance the EL properties; the QD light-emitting diode (QD-LED) performance was also investigated. Thermogravimetric and ¹H nuclear magnetic resonance analyses were used to examine the bipyridyl-ligand-partially-substituted QDs. Photoluminescence spectroscopy and transmission electron microscopy revealed that the emission wavelength (630 nm) and size (7.3 nm) of the QDs were not altered upon ligand exchange. Significant improvements were observed in the electronic properties of QD-LED devices fabricated using the bipyridyl-ligand-substituted QDs. The bipyridyl ligands lowered the charge-injection barrier and improved the charge balance in the QDs. High-performance QD-LED devices were consequently realized with an augmentation of two times in current density, and three times in brightness, external quantum efficiency, and current efficiency.     

Thermal delocalization of carriers in semiconductor lasers (λ = 1010–1070 nm)

The temperature dependences of the emission characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures (wavelengths ?? = 1010?C1070 nm) have been studied. It was found that, in the continuous-wave mode, the main mechanism of ??saturation?? of the light-current characteristic with increasing temperature of the active region is carrier delocalization into the waveguide layer. It was experimentally demonstrated that the thermal delocalization of carriers depends on the energy depth of the quantum well (QW) in the active region. It is shown that the minimum internal optical loss at 140°C is obtained in laser structures with the largest energy depth of the QW of the active region.     

InGaAsSb(Gd)/InAsSbP double heterostructure lasers (λ=3.0–3.3 µm) for diode laser spectroscopy

Data on threshold currents, the differential quantum efficiency, the emission spectrum, current tuning, and radiation power of mesastripe InGaAsSb(Gd)/InAsSbP double heterostructure lasers with λ=3.0–3.3 µm and a cavity length of 70–150 µm in a temperature range of 50–107 K are reported. In the experiments, the threshold currents I _th<10 mA, a total output power of 0.5 mW/facet, and a single-mode power of 0.43 mW at 77 K in the cw regime were obtained. Lasers operated in the single-mode regime at currents I≤6I _th, the spectral purity was as high as 650: 1, the tuning rate was 210 cm^?1/A, and the tuning range was 10 cm^?1 wide. An example of methane detection at 3028.75 cm^?1 is presented.     

3.7~4.8 μm红外二次成像折反射式光学系统设计

为满足小、远目标和空间目标的光学特性测量需求,提出以RC结构为设计基础,通过曲线方程和高斯公式确立反射式光学系统初始结构参数。为达到优化设计目的,结构中引入了二次成像中继镜组,解决了100%冷光阑效率问题。通过ZEMAX建立评价函数,仿真测试表明:设计完成的红外二次成像折反射式光学系统口径200 mm,焦距380 mm,结构紧凑简单,成像质量满足实际测量需求。