Cyclotron resonance in Hg1−xCdxTe at 337 micrometre in the range 77 K – 150 K

Cyclotron resonance experiments have been performed in transmission at 337 μm on Hg_1?xCd_xTe single crystals with x = 0.20 and 0.215, at temperatures between 77 and 150 K.     

The polar magneto-optic Kerr rotation of ferromagnetic perovskites (La,Bi, Sr)MnO3

The polar magneto-optic Kerr rotation of the perovskites Bi_xLa_1?x?y Sr_yMnO₃ is reported for wavelengths between 0.25 and 0.7 μm at 78 and 300 K. The presence of bismuth enhances strongly the Kerr rotation around 0.27 μm at 78 K (for x = 0.25 and y = 0.3 the rotation is 2.3 deg at 0.29 μm).     

Side optical cavity,single quantum well diode laser

Large optical cavity single quantum well PbEuSeTe diode lasers recently attained the highest temperatures yet observed to our knowledge for long wavelength (g > 3)m) diode lasers. Current studies of PbTe/PbEuSeTe quantum wells by transport and luminescence techniques suggest that most of the band edge offset at a PbTe/PbEuSeTe heterojunction is in the valence band. Thus a 3odified, side optical cavity single quantum well structure was grown in which the PbTe quantum well active region was placed at one side of the large optical cavity to maximize the potential barrier and, therefore, limit the electron leakage out of the quantum well. This resulted in the lowest threshold currents we have yet observed in these devices — 10 mA at 80 K and 120 mA (1.6 KA/cm²) at 160 K under CW conditions. This device lased at up to 175 K CW (g = 4.47)m), which is the highest CW lasing temperature that we have observed so far. These results support the finding that the conduction band offset is relatively small in PbTe/PbEuSeTe heterojunctions.     

Si/Si1−xGex/Si-based quantum wells infrared photodetector operating at 1.55 μm

A quantum well infrared photodetector consisting of self-assembled type II SiGe/Si based quantum wells operating around 1.55 μm at room temperature has been investigated. The Si_1−yGe_y/Si/Si_1−xGe_x/Si/Si_1−yGe_y stack results in a ‘W’ like profiles of the conduction and valence bands strain-compensated in the two low absorption windows of silica fibers infrared photodetectors have been proposed. Such computations have been used for the study of the p-i-n infrared photodetectors operating, around (1.3–1.55 μm) at room temperature. The quantum transport properties of electrons and holes were approved with Schrödinger and kinetic equations resolved self-consistently with the Poisson equation. The theoretical performances of the photodetector were carried out such as the dark current mechanisms, the temperature dependence of normalized dark current and the zero-bias resistance area product (R₀A).     

Dual-wavelength stimulated emission from a double-layer Cd x Hg1 − x Te structure at wavelengths of 2 and 3 μm

Dual-wavelength stimulated emission from a double-layer Cd _x Hg_{1 ? x} Te heterostructure optically pumped by a pulsed Nd:YAG laser at temperatures T = 77–150 K is reported. The emission spectral lines have been observed at wavelengths λ₁ ～ 2 μm and λ₂ ～ 3 μm. Emission spectra recorded at different temperatures are presented.     

Investigation of p-type strained-layer InxGa1−xAs/AlyGa1−yAs quantum well infrared photodetectors for long wavelength infrared imaging arrays applications

Two p-type compressively strained-layer (PCSL) In_xGa_1−xAs/Al_yGa_1−yAs (where,x=0.4, 0.2;y=0, 0.15) quantum well infrared photodetectors (QWIPs) grown by MBE on (100) semi-insulating (SI) GaAs substrates have been investigated for 3-5 μm MWIR and 8-14 μm LWIR imaging arrays applications. The In_0.4Ga_0.6As/GaAs PCSL-QWIP utilizing the resonant transport mechanism between the heavy-hole type-I states and the light-hole type-II states shows a broadband double-peak response between 8 and 9 μm range. Using compressive-strain in the InGaAs quantum well, normal incident absorption was greatly enhanced by reducing the heavy-hole effective mass and increasing the density of states in the off-zone center. Maximum responsivities of 93 mA W⁻¹and 30 mA W⁻¹were obtained at peak wavelengths of λ_p1=8.9 μm and λ_p3=5.5 μm, respectively atV_b=1.6 V, and detectivity (D*) at λ_p1=8.9 μm was found to be 4.0×10⁹cm−√Hz/WatV_b=0.3 V andT=75 K for this QWIP. The In_0.2Ga_0.8As/Al_0.15Ga_0.85As PCSL-QWIP achieves two-color detection with peak wavelengths at 7.4 μm in the LWIR band and 5.5 μm in the MWIR band. This detector is under background limited performance (BLIP) atT=63 K for biases varying from −2.7 V to +3 V. A detectivity (D*) of 1.06×10¹⁰cm √Hz/Wwas obtained at λ_p7.4 μm,V_b1.0 V andT=81 K for this QWIP.     

High-temperature operation of AlGaInAs/InP lasers1994

We discuss the design of uncooled lasers which minimizes the change in both threshold current and slope efficiency over the temperature range from–40 to +85°C [1]. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the Al _x Ga _y In_1–x–y As/InP material system [1] instead of the conventional Ga _x In_1–x As _y P_1–y /InP material system. Experimentally, we have investigated strained quantum well lasers with three different barrier layers and confirmed that the static and dynamical performance of the lasers with insufficient carrier confinement degrades severely under high-temperature operation [2]. With an optimized barrier layer, the Al _x Ga _y In_1–x–y As/InP strained quantum well lasers show superior hightemperature performance, such as a small drop of 0.3 dB in slope efficiency when the heat sink temperature changes from 25 to 100°C [3], a maximum CW operation temperature of 185°C [4], a thermally-limited 3-dB bandwidth of 13.9 GHz at 85°C [2], and a mean-time-to-failure of 33 years at 100°C and 10 mW output power [5].     

Quantum wells under an in-plane magnetic field: Effect of the composition parameters on excited electron energy splitting

The dependence of the electronic spin-splitting energy on the composition parameters (x,y) in In_xGa_1?xAs–In_yAl_1?yAs-based quantum wells, has been calculated. InGaAs narrow gap structures, subjected to in-plane magnetic fields, have been selected because these structures have a big Landè factor. The dependence of the Landé factor both on the applied fields and composition parameters has been included for fixed well width and external electric field. Contributions from the interfaces and strain, which also depend on the composition, are included. Spin-splitting energy and density of states show a strong dependence on the above parameters.     

Band edge offsets in strained (InGa)As-(AlGa)As heterostructures

The excitonic transitions between the ground electron and hole quantum well sublevels in strained In_xGa_1-xAs-Al_yGa_1-yAs multiple quantum well structures (x = 0.12−0.35 and y = 0.2−0.35) have been investigated by means of photoluminescence and photoconductivity measurements. The molecular beam epitaxy grown structures contained an Al_yGa_1-yAs matrix with one unstrained GaAs and three strained In_xGa_1-xAs quantum wells one of which was in the GaAs cladding layers. The ratio of the conduction band edhe line up to the band gap offset for the strained In_xGa_1-xAs-unstrained Al_yGa_1-yAs interface has been found to be 0.67 ± 0.08 for the studied regions of x and y.     

Subband transitions in AlxGa1−xN /GaN/ AlxGa1−xN and AlxGa1−xN /InN/ AlxGa1−xN single quantum wells

We have calculated the spectral regime of subband transitions in Al_xGa_1−xN/GaN and Al_xGa_1−xN/InN single quantum wells. We used a simplified model to account for the internal electric fields, which modify the shape of the quantum well. Some of the parameters for these materials have not yet been firmly established. Therefore, we carried out the analysis for the extremes of the reported values of conduction band discontinuities and band gaps (in the case of InN). This analysis shows that the spectral regime of interband transitions for 1–4 nm thick wells has wavelengths above 0.5 μm for AlGaN/InN and above 0.8 μm for AlGaN/GaN and both heterostructures cover several μm wavelengths. The spectral variation with alloy composition is less pronounced in the Al_xGa_1−xN/InN single quantum wells due to the higher electric field present across the InN quantum well as compared to GaN. The results of these calculations are in good agreement with more rigorous theoretical approaches and available experimental values for Al_xGa_1−xN/GaN.     

Synthesis and TL glow curve analysis of BaSO4:Eu,Dy phosphor

The polycrystalline samples of Ba_1?x?ySO₄:Eu_x,Dy_y (0≤x≤1, 0≤y≤1) have been prepared using the chemical co-precipitation technique. The thermoluminescence (TL) sensitivity of the samples have been found changing with the value of x and y and the highest TL intensity is for Ba₉₆SO₄:Eu₀₂,Dy₀₂. The sample has been characterised by x-ray diffraction (XRD). The samples are found to have orthorhombic structure. For TL analysis Ba₉₆SO₄:Eu₀₂,Dy₀₂ is annealed at different temperatures ranging from 873 to 1173 K. Kinetic parameters of all the TL glow curves of Ba_1?x?ySO₄:Eu_x,Dy_y for different values of x and y and also for the TL glow curves Ba₉₆SO₄:Eu₀₂,Dy₀₂ annealed at different temperatures have been found out using computerised glow curve deconvolution (CGCD) method. The activation energy for the most intense TL peak at (444–453 K) is found out to be 1.26 eV and order of kinetics is 1.35.     

Optical coefficients of Hg1 − x − y Cd x Eu y Se crystals

Optical properties of Hg_{1 ? x ? y} Cd _x Eu _y Se crystals grown by the Bridgman method have been investigated based on the independent reflectance and transmittance measurements, which were performed on a Nicolet 6700 spectrometer at T = 300 K in the wavelength range 0.9 ≤ λ ≤ 26.6 μm. The values of refractive index n, absorption index k, and absorption coefficient α have been determined for the crystals studied. Based on the dependences α = f(hν), the presence of direct allowed interband optical transitions in the crystals is established and the band-gap values are determined. The influence of temperature on the transmittance and band gap are investigated in the range T = 114–300 K.     

CW and pulsed Pb1–xSnxSe diode laser spectroscopy of 14NH3 and 15NH3 molecules

The absorption spectra of ¹⁴NH₃ and ¹⁵NH₃ molecules from 930 cm^-1 to 1220 cm^-1 have been obtained with CW and pulsed Pb_1–xSn_xSe diode lasers. The laser emission frequency has been tuned by varying crystal composition, diode temperature, hydrostatic pressure, or injection current. The registration of the absorption spectra with CW PbSe laser continuously tuned by varying hydrostatic pressure has been accomplished. The possibility of gas isotope abundancies measurements by diode lasers is considered.     

A simple model for optimization design of high performance In1−x−y Ga y Al x As strained MQW DFB lasers

It is well known that complex rate equations and the couple wave equation have to be solved by the method of iteration in the simulation of multi-quantum well (MQW) distributed feedback Bragg (DFB) lasers, and a long CPU time is needed. In this paper, from the oscillation condition of lasers, we propose a simple and fast model for optimization of In_1–x–y Ga _y Al _x As strained MQW DFB lasers. The well number and the cavity length of 1.55 m wavelength In_1–x–y Ga _y Al _x As MQW DFB lasers are optimized using the model. As a result, the simple model gives almost the same results as the complex one, but 90% CPU time can be saved. In addition, a low threshold, high maximum operating temperature of 550–560 K, and high relaxation oscillation frequency of over 30 GHz MQW DFB laser is presented.     

Magnetic transitions in LaFe13−x−yCoySix compounds

The magnetic properties of a set of LaFe_13?x?yCo_ySi_x compounds (x = 1.6 ? 2.6; y = 0, y = 1.0) have been investigated using magnetic measurements, thermal expansion, ⁵⁷Fe Mössbauer spectroscopy and high resolution neutron powder diffraction methods over the temperature range 10–300 K. The natures of the magnetic transitions in these LaFe_13?x?yCo_ySi_x compounds have been determined. The Curie temperatures of LaFe_13?xSi_x were found to increase with Si content from T_C = 219(5) K for Si content x = 1.6 to T_C = 250(5) K for x = 2.6. Substitution of Co for Fe in LaFe_10.4Si_2.6 resulted in a further enhancement of the magnetic ordering temperature to T_C = 281(5) K for the LaFe_9.4CoSi_2.6 compound. The nature of the magnetic transition at the Curie temperature changes from first order for LaFe_11.4Si_1.6 to second order for LaFe_10.4Si_2.6 and LaFe_9.4CoSi_2.6. The temperature dependences of the mean magnetic hyperfine field values lead to T_C values in good agreement with analyses of the magnetic measurements. The magnetic entropy change, ?ΔS_M, has been determined from the magnetization curves as functions of temperature and magnetic field (ΔB = 0 ? 5 T) by applying the standard Maxwell relation. In the case of LaFe_12.4Si_1.6 for example, the magnetic entropy change around T_C is determined to be -ΔS_M ～ 14.5 J kg^?1 K^?1 for a magnetic field change Δ B = 0 ? 5 T.     

Exciton capture and thermal escape in InAs dot-in-a-well laser structures

The photoluminescence (PL), its temperature and power dependences have been studied in InAs quantum dots (QDs) embedded in asymmetric In_xGa_1?y As/GaAs quantum wells (QWs) with variable In_xGa_1?x As compositions in the capping layer. Three stages for thermally activated decay of QD PL intensity have been revealed. A set of rate equations for exciton dynamics (relaxation into QWs and QDs, and thermal escape) are solved to analyze the mechanism of PL thermal decay. The variety of PL intensities and peak positions, as well as the activation energies of PL intensity decay in DWELL structures with different compositions of a capping layer are discussed.     

Classical and quantum hall effect measurements in GaInNAs/GaAs quantum wells

We have performed magneto-transport experiments in modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells with nitrogen mole fractions 0.4%, 1.0% and 1.5%. Classical magnetotransport (resistivity and low-field Hall effect) measurements have been performed in the temperatures between 1.8 and 275 K, while quantum Hall effect measurements in the temperatures between 1.8 and 47 K and magnetic fields up to 11 T.The variations of Hall mobility and Hall carrier density with nitrogen mole fractions and temperature have been obtained from the classical magnetotransport measurements. The results are used to investigate the scattering mechanisms of electrons in the modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells. It is shown that the alloy disorder scattering is the major scattering mechanism at investigated temperatures.The quantum oscillations in Hall resistance have been used to determine the carrier density, effective mass, transport mobility, quantum mobility and Fermi energy of two-dimensional (2D) electrons in the modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells. The carrier density, in-plane effective mass and Fermi energy of the 2D electrons increases when the nitrogen mole fraction is increased from y=0.004 to 0.015. The results found for these parameters are in good agreement with those determined from the Shubnikov-de Haas effect in magnetoresistance.     

Electron paramagnetic resonance of Gd3+ ions in Ca1 − x − y Y x Gd y F2 + x + y crystals

Electron paramagnetic resonance of Ca_{1 ? x ? y} Y _x Gd _y F_{2 + x + y} single crystals has revealed spectra that are not typical of gadolinium-doped CaF₂ crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd³⁺ ions localized in yttrium clusters. Weak spectra of tetragonal Gd³⁺ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd³⁺ ion, have been also detected. These centers are attributed to isolated Gd³⁺ ions localized near octahedral rare-earth clusters or their associations.     

Optical properties of GaN x As y P1?x?y semiconductor quaternary solid solutions

The photoluminescence method was used in the temperature range of 15?C300 K to study the optical properties of quantum-dimensional heterostructures based on GaN _x As _y P_(1?x?y) solid solutions, synthesized on the surface of a GaP (100) substrate. The calculations for the band-gap width of the GaN _x As _y P_(1?x?y) solid solution with the use of the band anticrossing model are shown to agree well with experimental data.     

Design of strain compensated InGaAs/GaAsSb type-II quantum well structures for mid-infrared photodiodes

In this paper, the transition wavelength and wave function overlap of type-II In_xGa_1-xAs/GaAs_1-ySb_y quantum wells are numerically calculated using a 4-band k · p Hamiltonian model. The simulation results indicate that absorption wavelength from 2 to 4?μm can be achieved with a strain compensated quantum well structure. The transition wavelength and wave function overlap can be optimized by properly selecting the thicknesses and composition of the quantum well layers.