Optical and structural properties of molecular-beam epitaxially grown Ga0.47In0.53As/Al0.48In0.52As superlattices,emitting at 1.55 μm at room temperature

We have combined photoluminescence and absorption measurements with double crystal x-ray diffraction in order to study the influence of growth conditions on optical and structural properties of Ga_0.47In_0.53As/Al_0.48In_0.52As superlattices of 10.5 nm well width grown by molecular beam epitaxy on InPSn substrates. Superlattices with excellent structural properties can be grown even at low substrate temperatures of 500 °C, as indicated by narrow linewidths of the satellite peaks of the x-ray diffraction pattern of 20 to 25 s of arc (FWHM). However, elevated substrate temperatures are required to increase the intensity of the intrinsic luminescent subband transition at 77 K, to reduce the luminescence linewidth to 12 meV (FWHM), and to sharpen the absorption spectra. In addition to the absorption due to the steplike variation of the two-dimensional density of states, we observe excitonic transitions to the excitonic continuum at the subband edges.     

Flat Top Optical Frequency Combs Based on a Single-Core Quantum Cascade Laser at Wavelength of ～8.7 μm

We present optical frequency combs with a spectral emission of 48 cm^-1and an output power of 420 m W based on a single-core quantum cascade laser at λ ～ 8.7μm. A flat top spectrum sustains up to 130 comb modes delivering ～ 3.2 m W of optical power per mode, making it a valuable tool for dual comb spectroscopy. The homogeneous gain medium, relying on a slightly diagonal bound-to-continuum structure, promises to provide a broad and stable gain for comb operating. Remarkably, the dispers...     

Performance of In0.47Ga0.53As metal-semiconductor-metal hybrid receiver at 1.55 μm

We report on the performance at 1.55 m of a hybrid receiver combining an In_0.47Ga_0.53As metal-semiconductor-metal photodetector (with buried AllnAs buffer layer) with a GaAs MESFET preamplifier. A bit error rate of 10^-9 is measured at 1 Gbps with nonreturn to zero pseudorandom bit sequence (2¹⁵–1) at a received optical power of –19 dBm. Modification of the preamplifier design and a reduction of bond pad size could improve the sensitivity by 6–7 dB.     

Relaxation oscillations and damping factors of 1.3 μm In(Ga)As/GaAs quantum-dot lasers

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 10¹⁰ cm^–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm². The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10^–16 cm² and 3.4 × 10 ^–17 cm ³, respectively. Using these parameters, the maximum modulation bandwidth f _{3 dB max} is estimated as 7.9 GHz.     

Influence of Growth Parameters of Frequency-Radio Plasma Nitrogen Source on Extending Emission Wavelengths from 1.31 μm to 1.55 μm GaInNAs/GaAs Quantum Wells Grown by Molecular-Beam Epitaxy

High （42.5%） indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3μm to 1.5μm range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy, The growth parameters of plasma power and N2 flow rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54μm GaInNAs/GaAs QWs was kept as comparable as that in 1.31 μm.     

Materials and device properties of pseudomorphic In x Ga1−x As/Al0.3Ga0.7As/GaAs high electron mobility transistors (0<x<0.5)

Modulation doped Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures for device application have been grown using molecular beam epitaxy. Initially the critical layer thickness for InAs mole fractions up to 0.5 was investigated. For InAs mole fractions up to 0.35 good agreement with theoretical considerations was observed. For higher InAs mole fractions disagreement occurred due to a strong decrease of the critical layer thickness. The carrier concentration for Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures with a constant In _x Ga_1–x As quantum well width was investigated as a function of InAs mole fraction. If the In _x Ga_1–x As quantum well width is grown at the critical layer thickness the maximum carrier concentration is obtained for an InAs mole fraction of 0.37. A considerable higher carrier concentration in comparison to single-sided -doped structures was obtained for the structures with -doping on both sides of the In _x Ga_1–x As quantum well. Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures with InAs mole fractions in the range 0–0.35 were fabricated for device application. For the presented field effect transistors best device performance was obtained for InAs mole fractions in the range 0.25–0.3. For the field effect transistors with an InAs mole fraction of 0.25 and a gate length of 0.15 m a f _T of 115 GHz was measured.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Optical and electrical properties of modulation-doped n and p-type Ga x In1-x N y As1-y /GaAs quantum wells for 1.3 μm laser applications

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga_1-x In _x N _y As_1-y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (dE/dT) is tabulated as a function of nitrogen concentration and the type of dopant.     

Phase transitions of YbX (X = P,As and Sb) with a NaCl-type structure at high pressures

The powder X-ray diffraction of YbX (X?=?P, As and Sb) with a NaCl-type structure has been studied with synchrotron radiation up to 63?GPa at room temperature. YbSb undergoes the first-order structural phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure at around 13?GPa. The structural change to the B2 structure occurs with the volume collapse of about 1% at 13?GPa. The transition pressure of YbSb is surprisingly lower than that of any other heavier LnSb (Ln?=?Dy, Ho, Er, Tm and Lu). The pressure-induced phase transitions in YbP and YbAs are observed at around 51?GPa and 52?GPa respectively. The transition pressure of both compounds is much higher than that of YbSb. The high-pressure structural behaviour of YbX (X?=?P, As and Sb) is discussed. The volume versus pressure curve for YbX with the NaCl-type structure is fitted by a Birch equation of state. The bulk moduli of these compounds with the NaCl-type structure are 104?GPa for YbP, 85?GPa for YbAs and 52?GPa for YbSb.     

Half-metallic behavior of Co2YZ (Y = V,Cr; Z = Al,Ga) under pressure: a DFT study

The structural, electronic and magnetic properties of Co-based Heusler compounds Co₂YZ (Y = V, Cr; Z = Al, Ga) under pressure are studied using first principles density functional theory. The calculations are performed within generalized gradient approximation. The total magnetic moment decreases slightly on compression. Under application of external pressure, the valence band and conduction band are shifted downward which leads to the modification of electronic structure. There exists an indirect band gap along Г–X for all the alloys studied. Co₂CrAl shows half-metallic nature up to 85 GPa. After this pressure transition from true half-metallic behavior to nearly half-metallic behavior is observed and at 90 GPa it shows metallic behavior. Co₂CrGa shows nearly half-metallic behavior at ambient pressure, but true half-metallic behavior is observed as pressure is increased to 100 GPa. For Co₂VGa, true half-metallic to nearly half-metallic transition is observed at 40 GPa and around 100 GPa, Co₂VGa shows metallic behavior. For Co₂VAl, true half-metallic behavior is not observed at ambient as well as higher pressures. The half metal-to-metal transition in Co₂VAl and Co₂CrAl is accompanied by quenching of magnetic moment.     

Elastic and thermodynamical properties of A15 Nb3X (X = Al,Ga, In,Sn and Sb) compounds — First principles DFT study

Elastic and thermodynamical properties of Nb₃X (X = Al, Ga, In, Sn and Sb) compounds are obtained by performing the band structure calculations, using the FP-LAPW method. The calculated lattice constants, elastic constants, Bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Debye temperature and anisotropy ratio are reported and the results agree with the available data. From the present study, it is observed that stiffness and shear resistance are found to be greater in Nb₃Sb than in other compounds. It is more brittle in nature and comparatively harder than other materials under study. The degree of anisotropy decreases as one moves across Nb₃Ga, Nb₃Al, Nb₃In, Nb₃Sb and Nb₃Sn. From the calculated values of the Debye temperature, it is observed that thermal conductivity is greater for Nb₃Sb and less for Nb₃In.     

Generation of Broadband Near-Infrared (2–2.5 μm) Radiation from an Optical Parametric Amplifier Driven by a Cr:Forsterite Laser Near Dispersion Anomalies of Tuning Curves

Pulses with a spectral width of 450 nm at a wavelength of 2.2 μm are generated in a parametric amplifier based on a type-I BBO crystal pumped by the second harmonic (620 nm) of a Cr:forsterite laser. Such a broadband radiation is obtained in a specific regime of the group velocity matching near the vertical region of the tuning curve. The generated pulses can be compressed to a duration of about 2.5 optical cycles (34 fs) in a medium with positive group-velocity dispersion.     

Structural phase transition behaviour of ZnaSb3 and its substitutional compounds （Zn0.98M0.02）4Sb3 （M = Al,Ga and In） at low temperatures

Structural phase transitions of Zn4Sb3 and its substitutional compounds (Zn0.98M0.02)4Sb3 (M = Al, Ga and In) are investigated by electrical transport measurement and differential scanning calorimetry below room temperature. The results indicate that both β→α and α→α′ phase transitions of Zn4Sb3 are reversible and exothermic processes, which may be explained as that both the transitions originate from the ordering of the disordered interstitial Zn and vacancies in regular sizes. The derived activation energies of β→α and α→α′ phase transition processes for Zn4Sb3 are E1 = 3.9 eV and E2 = 4.1 eV, respectively. Although no remarkable influence on activation energy E2 is observed after Al doping, Al substitution for Zn causes E1 to increase to 4.6 eV, implying its suppression of βα transition to a great extent. Moreover, it is found that both βα and αα′ transitions are completely prohibited by substitution of either In or Ga for Zn in Zn4Sb3. The underlying mechanisms for these phenomena are discussed.