Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 μm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm⁻¹ (for λ≈1.08 μm) in an asymmetric waveguide 4 μm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm⁻¹ was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 μm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-μm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 12, 2004, pp. 1477–1486. Original Russian Text Copyright ? 2004 by Slipchenko, Vinokurov, Pikhtin, Sokolova, Stankevich, Tarasov, Alferov.     

High-power light-emitting diodes operating in the 1.9 to 2.1-µm spectral range

Light-emitting diodes (LED’s) operating in the spectral range 1.9–2.1 μm have been fabricated by liquid-phase epitaxy on the basis of AlGaAsSb/GaInAsSb double heterostructures with a high Al (64%) content in the wide-gap regions. The design of the LED makes it possible to locate the active region near the heat-removal elements of the housing, and pass the light through the GaSb substrate, which is completely unshielded by the contact. The LED’s are investigated in the quasi-continuous (CW) regime and pulsed regime at room temperature. The optical power of the LED’s possesses a linear current dependence over a wide range of currents. A CW optical power as high as 4.6 mW and a peak optical power of 190 mW in the pulsed regime were achieved at room temperature. It is shown that the transition from linear to sublinear current dependence of the optical power is governed by Auger recombination in the pulsed regime at pulse durations as low as 5 μs. Fiz. Tekh. Poluprovodn. 33, 239–242 (February 1999)     

Comparative analysis of long-wavelength (1.3 µm) VCSELs on GaAs substrates

Two designs of vertical-cavity surface-emitting lasers (VCSELs) for the 1.3 μm spectral range on GaAs substrates with active regions based on InAs/InGaAs quantum dots and InGaAsN quantum wells are considered. The relationship between the active region properties and optical microcavity parameters required for lasing has been investigated. A comparative analysis is made of VCSELs with active regions based on InAs/InGaAs quantum dots or on InGaAsN quantum wells, which are fabricated by MBE and demonstrate room-temperature CW operation. Optimization of the vertical microcavity design provides single-pass internal optical losses lower than 0.05%. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 7, 2001, pp. 881–888. Original Russian Text Copyright ? 2001 by Maleev, Egorov, Zhukov, Kovsh, Vasil’ev, Ustinov, Ledentsov, Alferov.     

Analysis of threshold current density and optical gain in InGaAsP quantum well lasers

Single-mode and multimode quantum well (QW) laser diodes with emission wavelengths λ=1.0 and 1.58 μm, based on MOCVD-grown separate-confinement heterostructures, have been studied. An analysis of the threshold current density and optical gain is made on the basis of experimental dependences of the threshold current and differential quantum efficiency on the cavity length. The threshold current is decomposed into principal components in terms of model approximations taking into account the Auger recombination, ejection of electrons from QWs into waveguide layers, and lateral current spreading to passive regions of a mesa-stripe laser. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 3, 2002, pp. 364–374. Original Russian Text Copyright ? 2002 by Pikhtin, Sliptchenko, Sokolova, Tarasov.     

High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring

High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009. Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev.     

InGaAs/InP heterostructures with strained quantum wells and quantum dots (λ=1.5–1.9 µm)

Strongly strained In_xGa_1−x As/In_0.53Ga_0.47As/InP heterostructures with indium content x=0.69−1.0 in the active region were investigated experimentally and theoretically. Two types of structures were obtained by vapor-phase epitaxy from metalorganic compounds: 1) with isolated compression-strained quantum wells and 2) with self-organized nanosize InAs clusters (quantum dots). The temperature dependence of the quantum radiation efficiency of samples with quantum wells in the temperature range 77–265 K is characterized by T ₀=43 K. One reason for the low value of T ₀ is electron delocalization in the active region. The maximum radiation wavelength obtained in structures with quantum dots is 1.9 μm at 77 K. Fiz. Tekh. Poluprovodn. 33, 1105–1107 (September 1999)     

Heteroepitaxy of HgCdTe(112) infrared detector structures on Si(112) substrates by molecular-beam epitaxy

High-quality, single-crystal epitaxial films of CdTe(112)B and HgCdTe(112)B have been grown directly on Si(112) substrates without the need for GaAs interfacial layers. The CdTe and HgCdTe films have been characterized with optical microscopy, x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. HgCdTe/Si infrared detectors have also been fabricated and tested. The CdTe(112)B films are highly specular, twin-free, and have x-ray rocking curves as narrow as 72 arc-sec and near-surface etch pit density (EPD) of 2 × 10⁶ cm⁻² for 8 μm thick films. HgCdTe(112)B films deposited on Si substrates have x-ray rocking curve FWHM as low as 76 arc-sec and EPD of 3-22 × 10⁶ cm⁻². These MBE-grown epitaxial structures have been used to fabricate the first high-performance HgCdTe IR detectors grown directly on Si without use of an intermediate GaAs buffer layer. HgCdTe/Si infrared detectors have been fabricated with 40% quantum efficiency and R₀A = 1.64 × 10⁴ Ωm₂ (0 FOV) for devices with 7.8 μm cutoff wavelength at 78Kto demonstrate the capability of MBE for growth of large-area HgCdTe arrays on Si.     

Influence of the thickness change of the wave-guide layers on the threshold current of GaAs-based laser diode

The paper mainly deals with theoretical investigations of the effect of the thickness change of the waveguide layers on the threshold current. It is analyzed according to the result of a numerical simulation that asks how does the shift of the active region position affect the threshold current for a single quantum well (SQW) and double quantum well (DQW) laser diode (LD) with a relatively narrow waveguide. It is found that the variation trend of threshold current and optimum position of QW are different in SQW and DQW LD with 0.2 μm-thick waveguide, which may be due to the higher variation rate of optical loss in DQW LD with the shift of the active region. It is also found that in terms of either SQW or DQW LD, the variation tendency of the threshold current with a different loss coefficient of the p-cladding layer makes little difference for the relatively narrow waveguide LD. Moreover, the variation trend of the threshold current and the optimum position of QW is almost the same in SQW and DQW LD with 0.8 μm-thick waveguide, because the optical loss is small enough and the threshold current is dominated by the optical confinement factor (OCF) in QW.     

Study on optical compund films

Using the compound materials and double e-gun evaporation ,the compound optical films have been successfully deposited on K9 glass substrate.The refractive index of optical compound films deposited in diffeent parameters have been measured and theoretical formula for calculation refractive index of compound films have been derived.Tt is shown that the experimental curve for the variation of re-fractive index with wavelength in 0.4-1.4цm region and the theoretical one agree very well.Using these films,the laser reflecting mirror has been successfully coat-ed.     

Study of the optical transmission enhancement properties in a one-dimensional Ag film with different single slit groove structures

Numerical simulation has been performed on the optical transmission enhancement properties of a one-dimensional Ag film single slit structure with grooves. The results show that the position, depth and number of the grooves have great influence on the optical transmission, and surface plasmon polariton and resonance mode are the primary factors. The maximal extinction ratio of 35.8 dB is achieved in the single slit structure by adjusting groove depth.     

Study of the optical transmission enhancement properties in a one-dimensional Ag film with different single slit groove structures

Numerical simulation has been performed on the optical transmission enhancement properties of a one-dimensional Ag film single slit structure with grooves. The results show that the position,depth and number of the grooves have great influence on the optical transmission,and surface plasmon polariton and resonance mode are the primary factors. The maximal extinction ratio of 35.8 dB is achieved in the single slit structure by adjusting groove depth.     

Metal-organic vapor-phase epitaxial growth of HgCdTe device heterostructures on three-inch-diameter substrates

A new metal-organic vapor-phase epitaxial (MOVPE) reactor-cell design has been developed to grow on 3-in.-diameter substrates. This was required to produce uniform, fully doped heterostructures needed for array producibility and wafer-scale processing compatibility. The reactor has demonstrated epitaxial growth of HgCdTe (MCT) with good morphology onto both GaAs and GaAs on Si wafers. The density of surface-growth defects, typical of MOVPE growth, has been reduced to <5 cm⁻² at a sufficient yield to make the production of low cluster-defect, two-dimensional (2-D) arrays possible. The new horizontal reactor cell uses substrate rotation to achieve improved uniformity and is able to incorporate substrates up to 4-in. diameter. Good compositional and thickness uniformity was achieved on epilayers grown on 3-in.-diameter, low-cost GaAs and GaAs on Si wafers. Sufficient uniformity has been achieved to produce 12 sites of full-TV format 2-D arrays per slice. To yield the benefits of heterostructure design, the MCT epilayers also needed to demonstrate efficient and uniform activation of both arsenic (acceptor) and iodine (donor) dopants. Secondary ion mass spectrometry (SIMS) and Hall assessment showed that the uniformity of As and I doping was ±10%. Fully doped heterostructures have been grown to investigate the device performance in the 3–5 μm and 8–12 μm infrared bands. The 2-D array performance has shown that at 180 K near-background-limited performance (BLIP) diodes have been produced in the 3–5 μm band.     

Photovoltaic effect in an asymmetric GaAs/AlGaAs nanostructure produced as a result of laser excitation

Photocurrent has been observed in a GaAs/GaAlAs structure with three asymmetric quantum wells in a magnetic field H parallel to the surface of sample irradiated with a quasicontinuous-wave laser with λ=1.065 μm. The current flows in the plane of the layers in a direction perpendicular to the magnetic field. The magnitude of the current increases with H, and when the magnetic field is switched, the sign of the photocurrent changes. The effect is explained on the basis of a model with asymmetric electronic wave functions in a magnetic field. Fiz. Tekh. Poluprovodn. 31, 872–874 (July 1997)     

Size effect on optical performance of blue light-emitting diodes

In this paper,size effects on optical performance of blue light-emitting diodes(LEDs)are investigated.The essential physical mechanism is studied by fabricating LEDs with various sizes of the active area and testing optical characteristics.It is found that micro-LEDs have better light extracting efficiency and thermal dissipation compared with broad-area LEDs,which is likely due to the small ratio of perimeter and active area.Furthermore,micro-LEDs are more beneficial for displays due to the stable wavelength under the low pulse width modulation(PWM)current density.     

Monolayer-molybdenum-disulfide-based nano-optomechanical transistor and tunable nonlinear responses

Atomically thin two-dimensional semiconductor nanomaterials have attained considerable attention currently. Here, we present a nano-optomechanical system based on a suspended monolayer molybdenum disulfide (MoS₂). The linear and nonlinear coherent optical properties of this system, and the phenomenon of phonon-induced transparency are demonstrated. The transmission of the probe field can be manipulated by the power of a second ‘gating'' (pump) field, which indicates a promising candidate for an optical transistor. We further study the nonlinear effect of the system, and the optical Kerr effect of the monolayer MoS₂ resonator can be regulated under different parameter regimes. This scheme proposed here may indicate potential chip-scale applications of monolayer MoS₂ resonator in quantum information with the currently popular pump-probe technology.     

倾斜腔结构对量子点光有源器件性能的影响

Quantum-dot laser diodes （QD-LDs） with a Fabry-Perot cavity and quantum-dot semiconductor optical amplifiers （QD-SOAs） with 7° tilted cavity were fabricated. The infuence of a tilted cavity on optoelectronic active devices was also investigated. For the QD-LD, high performance was observed at room temperature. The threshold current was below 30 mA and the slope efficiency was 0.36 W/A. In contrast, the threshold current of the QDSOA approached 1000 mA, which indicated that low facet reflectivity was obtained due to the tilted cavity design. A much more inverted carrier population was found in the QD-SOA active region at high operating current, thus offering a large optical gain and preserving the advantages of quantum dots in optical amplification and processing applications. Due to the inhomogeneity and excited state transition of quantum dots, the full width at half maximum of the electroluminescence spectrum of the QD-SOA was 81.6 nm at the injection current of 120 mA, which was ideal for broad bandwidth application in a wavelength division multiplexing system. In addition, there was more than one lasing peak in the lasing spectra of both devices and the separation of these peak positions was 6-8 nm, which is approximately equal to the homogeneous broadening of quantum dots.     

Preparation of Indium Tin Oxide films deposited by reactive evaporation at different substrate-temperature and the properties

The Indium Tin Oxide films have been prepared at different substrate-temperature on glass substrates by reactive evapora- tion of In-Sn alloy with an oxygen pressure of 1.3 ×10-1 Pa and a deposition rate of 10-2 nm/s. The best ITO films obtained have an electrical resistivity of 4.35 × 10-4 ??cm , a carrier concentration of 4.02 × 1020 cm-3 , and a Hall mobility of 67.5 cm2v-1s-1. The influence of the substrate-temperature on the structural , optical and electrical properties of the obtained films has been investigated.     

Effect of the Structure and Valence State on the Properties of VO2 Thin Films

VO2 thin films with good switching properties were prepared by controlling the annealing time and the annealing temperature in a vacuum system.The structural,optical and electrical properties of the samples were cahracterized by using XRD,XPS,UV-VIS and electrical measurements.The witching parameters of VO2 thin film were investigated too.The results indicate that before and after phase transition the resistance of VO2 thin films changes aobut three orders of magnitude,the variation of film transmittance of 40% has been carried out with the absorptivity switching velocity of about 0.2607/min at 900 nm.The structural property of samples has been improved but the phase-transition properties have been decreased by increasing the annealing time and annealing temperature.The valence of V ions and the structure of samples have great effect on phase transition properties of VO2 thin films.Discussion on the effecs of annealing time and annealing temperature on the phase-transition temperature and hysteresis width shows that the best reasonable annealing tiem and annealing temperatre can be achieved.     

GaAs-based long-wavelength InAs bilayer quantum dots grown by molecular beam epitaxy

Molecular beam epitaxy growth of a bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated.The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot（BQD） structures is discussed.By optimizing the growth parameters,InAs BQD emission at 1.436μm at room temperature with a narrower FWHM of 27 meV was demonstrated.The density of QDs in the second layer is around 9×10⁹ to 1.4×10¹⁰ cm^-2. The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.     

Growth and characterization of Cd-Doped InGaAsP/InP double heterostructure lasers

The liquid phase epitaxial growth of Cd-doped InGaAsP/InP double heterostructure lasers (1.3 μm) has been studied. Cd has been found to have a smoothing effect on the morphology of the quaternary layers and a typical terracing effect on that of InP found also by doping with Zn. The defects, revealed by etching, were found to propagate in one to one correspondence from the substrate throughout the whole structure with no generation of defects even in a highly doped material. Electrical saturation at p ~2.10^l8Cm^-3 was found in InP by Hall measurements while no saturation was found in the quaternary up to a hole concentration of ~2.10^l9cm^-3. A lattice mismatch which is linearly dependent on the amount of Cd in the liquid was found by X-ray analysis. Cd was found to greatly facilitate the location of the p-n junction within the active region because of its low diffusion. Low threshold, very high external differential quantum efficiency, and high uniformity characterize the lasers made of this material. The results obtained in this work suggest that Cd should be considered as a promising candidate for a p-type dopant in fabrication of quaternary devices.