Optimization, design and fabrication of a non-cryogenic quantum infrared detector

A study of the optimization of the detectivity of a mid infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and give physical insight on the mechanisms dominating the dark current. The analysis is performed step by step, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure, doping density in the active region, on diffusion and generation–recombination mechanisms is analyzed. It is shown how the performances of a double heterostructure photovoltaic detector can be improved by a controlled doping the active region. Nevertheless, its development is still limited by the difficulties occurring during device processing. For example, the use of dry etching for the processing of InAs_0.91Sb_0.09 p–i–n photovoltaic detectors induces a strong leakage current along the mesa edge. In this letter, we show an improvement of the R₀A characteristic by several orders of magnitude at low temperature by using an Ion Beam Etching (IBE) followed by a wet chemical etching. This optimized and reliable device processing allows us to demonstrate that the detector performance is actually limited by the diffusion current of holes. Finally, we discuss the ability of an n-type barrier made of InAs/AlSb super-lattice to avoid hole diffusion and to improve the R₀A characteristic of these detectors. To cite this article: B. Vinter et al., C. R. Physique 4 (2003).     

Transport, optical and magnetotransport properties of hetero-epitaxial InAsxSb1−x/GaAs(x0.06) and bulk InAsxSb1−x (x0.05) crystals: experiment and theoretical analysis

We briefly review the growth and structural properties of InAs_xSb_1−x (x0.05) bulk single crystals and InAs_xSb_1−x (x0.06) epitaxial films grown on semi-insulating GaAs substrates. Temperature-dependent transport measurements on these samples are then correlated with the information obtained from structural (XRD, TEM, SEM) and optical (FTIR absorption) investigations. The temperature dependence of mobility and the Hall coefficient are theoretically modelled by exactly solving the linearized Boltzmann transport equation by inversion of the collision matrix and the relative role of various scattering mechanisms in limiting the low temperature and 300 K mobility is estimated. Finally, the first observation of Shubnikov oscillations in InAsSb is discussed.     

Kerr property of cubic K0.95Li0.05Ta0.60Nb0.40O3 single crystal

The Kerr (quadratic electro-optic) property of K_0.95Li_0.05Ta_0.60Nb_0.40O₃ was measured by using an automated scanning Mach–Zehnder interferometer. K_0.95Li_0.05Ta_0.60Nb_0.40O₃ has large Kerr effect with R₁₁ = 7.2 × 10⁻¹⁶ m²/V² and R₁₂ = −1.2 × 10⁻¹⁶ m²/V² at 632.8 nm near its phase-transition temperature. The dielectric and Kerr properties as function of temperature were also investigated, thus the quadratic polarization-optic coefficients were calculated. The values of g₁₁ and g₁₂ are 0.083 m⁴/C² and −0.014 m⁴/C², respectively, and do not depend on temperature within the measurement accuracy of 5%.     

The Mechanism of Magnetically Tuned Singlet–Triplet Avoided Crossings in the ÃA2– A1 40 Band of Thioformaldehyde H2C=S

Magnetically tuned singlet–triplet perturbations in the 4¹Ã¹A₂–2¹3¹ã³A₂ system of thioformaldehyde, found in ortho-rotational states (I = 1, the two hydrogen spins parallel) have been identified as being caused by vibronic spin–orbit coupling. This perturbation mechanism has been confirmed in several avoided crossings observed in this work for para states (I = 0, hydrogen spins antiparallel) which are much stronger. Parametrization of the theory has led to a quantitative understanding of the experimental frequency-field relations, and to an accurate prediction of the rovibrational energies of the triplet state. This in turn permitted the detection of about 100 Doppler-limited 2¹3¹ã³A₂–0^{0 1}A₁ rovibronic transitions which led into fine structure states. The combined data was then used to determine a set of rotational, fine, and hyperfine triplet-state parameters, the term value T₀(2¹3¹ã³A₂) = (16 685.385 ± 0.002) cm⁻¹, and the spin–orbit vibronic singlet–triplet coupling constant, W_ST = (0.0691 ± 0.0016) cm⁻¹. A large number of frequency perturbations observed in the crossings, ranging from 2 to 300 MHz, can be explained with this single parameter.     

Properties of YBa2Cu3O7−δ/YBa2CoxCu3−xOy/YBa2Cu3O7−δ Josephson edge junctions with 0.1 x 0.3 and the effect of flux flow on their normal resistance

YBa₂Cu₃O_7−δ (YBCO) based SNS edge junctions with cobalt doped YBCO barriers were prepared and characterized. At 77 K, good junctions had RSJ-like I–V curves with excess current, magnetic suppression of I_c of about 50% or more, and clear microwave steps. The conductance values 1/R_N at 77 K of junctions with different barrier thickness and composition, were proportional to the junction areas A, but show little correlation with the thickness of the barriers t_B in the range of 15t_B100nm. The corresponding I_cR_N products were observed to scale as J^0.66±0.09_c, similar to what was found by others. At the same time, the measured values of R_N are much smaller than what is expected based on the dimensions of the junction and the resistivity of the barrier material. To explain all of this, we propose a model in which at high supercurrent densities, flux flow of Josephson vortices in the junction leads to R_N values which are lower than expected. This model predicts

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, which fits the observed results very well.     

The structural, optical, and dielectric spectroscopy studies of novel ZnO–As2O3 glass system with Sb2O3 as additive

ZnO–As₂O₃–Sb₂O₃ glasses of varying concentrations of Sb₂O₃ with ZnO (ranging from 5 to 45 mol%) are prepared. A number of studies, including differential thermal analysis, and study of spectroscopic properties (viz., optical absorption and IR spectra) and dielectric properties (constant ε′, loss tan δ and ac conductivity σ_ac) over a wide range of frequency and temperature of these glasses are carried out. Analyses of the results of these investigations have indicated that the glasses containing higher concentrations of Sb₂O₃ are more suitable for non-linear optical (NLO) applications.     

Synthesis, characterization and magnetic properties on nanocrystalline BaFe12O19 ferrite

Single phase BaM (BaFe₁₂O₁₉) ferrites are prepared by using sol–gel method. The preparing conditions of samples are investigated in detail, such as acid/nitrate ratio, the value of pH and annealing temperature. The best conditions on preparing BaFe₁₂O₁₉, which can be obtained on a Fe/Ba ratio of 12, the citric acid contents R = 3, the starting pH of solution is 9, and annealing temperature 950 °C. The thermal decomposition behavior of the dried gel was examined by TG–DSC, the structure and properties of powders were measured respectively by XRD techniques. The magnetic properties of barium ferrites are emphatically researched about the changing crystallite size and annealing temperature by the vibrating sample magnetometer (VSM). Magnetic measurement shows that the barium ferrite samples annealed at 1000 °C has the maximal coercive field of 5691.91 Oe corresponding to the maximal remnant magnetization of 35.60 emu/g and the sample synthesized at 1000 °C has the maximal saturation magnetization of 60.75 emu/g.     

Bactericidal effects of Ag nanoparticles immobilized on surface of SiO2 thin film with high concentration

Bactericidal activity of high concentration Ag nanoparticles immobilized on surface of an aqueous sol–gel silica thin film was investigated against Escherichia coli and Staphylococcus aureus bacteria. Size of the surface nanoparticles was estimated in the range of 35–80 nm by using atomic force microscopy. Due to accumulation of the silver nanoparticles at near the surface (at depth of 6 nm and about 40 times greater than the silver concentration in the sol), the synthesized Ag–SiO₂ thin film (with area of 10 mm²) presented strong antibacterial activities against E. coli and S. aureus bacteria with relative rate of reduction of the viable bacteria of 1.05 and 0.73 h⁻¹ for initial concentration of about 10⁵ cfu/ml, respectively. In addition, the dominant mechanism of silver release in long times was determined based on water diffusion in surface pores of the silica film, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the Ag nanoparticles embedded near the surface of the SiO₂ thin film can be utilized in various antibacterial applications with a strong and long life activity.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Diffusion of silicon in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained film structure (B ₊ films) have been examined as diffusion barriers, preventing the silicon diffusion in silicon devices. The silicon diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) after annealing at temperatures up to 900° C, in view of application of high-temperature processes. The diffusivity from 400 to 900° C: D (m² s^–1)=2.5×10^–18 exp[–31 kJ/mol/(RT)] in B ₀ layers and D (m² s^–1)=3×10^–19 exp[–26 kJ/mol/(RT) in B ₊ TiN layers. The diffusivities determined correspond to grain boundary diffusion, the difference being due to the different microstructure. The very low diffusivity of silicon in B ₊ TiN layer makes it an excellent high-temperature barrier preventing silicon diffusion.     

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Ceramics with formula (1 − x)Pb(Zr_0.52Ti_0.48)O₃–x(Bi_3.25La_0.75)Ti₃O₁₂ (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.     

Magnetoresistance of the compound CeRu2Ge2

In this work we present a magnetoresistance study on the CeRu₂Ge₂ compound. We analyze the ρ(T) curves for several applied magnetic fields using the electron–magnon scattering model for a ferromagnetic spin arrangement. From this analysis, the field dependence of the energy gap of the magnon spectrum is obtained. The magnetoresistance ρ(H) at various temperatures arises from a normal metal contribution with an additional scattering mechanism due to electron–magnon interaction.     

Resonant-cavity-enhanced photodetectors and LEDs in the mid-infrared

In this paper we outline the use of resonant-cavity enhancement for increasing the exterior coupling efficiency of photodetectors and light-emitting diodes (LEDs) in the mid-infrared (MIR) spectral region. This method is potentially very important in the MIR because encapsulation is not presently feasible due to the lack of suitable materials. Among other potential applications, resonant-cavity-enhanced (RCE) photodetectors and LEDs could be particularly suitable for greenhouse gas detection because of their ‘pre-tunable’ spectrally narrowed resonantly enhanced peaks. We also present the optical characterization of an InAs RCE photodetector aimed at the detection of methane gas (λ≈3.3 μm), and an InAs/InAs_0.91Sb_0.09 resonant-cavity LED (RCLED) aimed at carbon dioxide gas (λ≈4.2 μm). The high peak responsivity of the RCE photodetector was 34.7 A/W at λ=3.14 μm, and the RCLED peaked at λ=3.96 μm. These are among the longest operating wavelengths for III–V RCE photodetectors and RCLEDs reported in the literature.     

The performance of Hg1−x Zn x Te photodiodes

This paper considers the Hg_1–x Zn _x Te alloy system as a potential material for the fabrication of infrared photodiodes. The influence of different junction current components (diffusion, tunneling and depletion layer currents) on the R ₀ A product of n⁺-pHg_1–x Zn _x Te photodiodes is analysed. The upper theoretical limits of the R ₀ A product and detectivity are determined. Results of calculations are compared with experimental data reported by other authors and those measured in our laboratory. Preliminary results on related technology and the properties of Hg_1–x Zn _x Te prepared by the ion-etching technique are presented.     

Numerical modeling of an InAsSb/InAsSbP double heterojunction light emitting diode for mid-infrared (2–5 μm) applications

The numerical model of a Mid-infrared (MIR) P⁺–InAs_0.48Sb_0.22P_0.30/n⁰–InAs_0.89Sb_0.11/N⁻–InAs_0.48Sb_0.22P_0.30 double heterostructure light emitting diode (DH-LED) has been reported in this paper. The governing equation of the structure has been solved numerically under the condition of high injection using fourth order Runge-Kutta method employing the shooting algorithm. The numerical model takes into account all dominant radiative and non-radiative recombination processes, surface recombination velocity and self-absorption in the active layer of DH-LED. The DH-LED has been simulated for mid-infrared applications by considering modulation bandwidth and its dependence on active layer width, doping concentration, and injected carrier density. The effect of surface recombination velocity on the quantum efficiency, peak light intensity for different values of active layer width and doping concentration has been estimated numerically. The rise time of the structure has been evaluated by considering transient response for a step current of 50 mA. The output power of DH-LED has been computed as a function of bias current and compared/ contrasted with the reported analytical and experimental results.     

High-performance pyroelectric single crystals for uncooled infrared detection applications

Uncooled pyroelectric infrared detectors based on ferroelectric single crystals 0.74Pb(Mg_1/3Nb_2/3)O₃–0.26PbTiO₃ (PMN–0.26PT) were fabricated. The performances of pyroelectric detectors dependence on detector fabrication temperature, absorption layer, and element thickness were compared. The room-temperature voltage responsivity (R_v) of 200 V/W and specific detectivity (D^*) of 10⁸ cm Hz^1/2/W at 12.5 Hz have been achieved. The results reveal that the better pyroelectric response can be expected by controlling temperature below 70 °C during the fabrication of the pyroelectric detectors, selecting absorption layer with high absorption coefficient, and decreasing the thickness of the elements.     

A Particle in a Magnetic Field of an Infinite Rectilinear Current

We consider the Schrödinger operator H=(i+A)² in the space L ₂(R ³) with a magnetic potential A created by an infinite rectilinear current. We show that the operator H is absolutely continuous, its spectrum has infinite multiplicity and coincides with the positive half-axis. Then we find the large-time behavior of solutions exp(–i H t)f of the time dependent Schrödinger equation. Our main observation is that a quantum particle has always a preferable (depending on its charge) direction of propagation along the current. Similar result is true in classical mechanics.     

La(Fe,Si)13-based magnetic refrigerants obtained by novel processing routes

The structure and magnetic properties of LaFe_13−xSi_x and Co-substituted LaFe_11.8−xCo_xSi_1.2 alloys prepared by melt spinning, as well as of LaFe_11.57Si_1.43H_x hydrides prepared by reactive milling are investigated. The hysteresis in the temperature- and field-induced phase transitions is significantly reduced as compared with conventional bulk alloys, which makes these materials very attractive for magnetic refrigerant applications. The unusual combination of features characteristic of first- and second-order phase transitions in the La(Fe,Si)₁₃-based compounds is discussed on the basis of density-functional electronic structure calculations.     

Synthesis and transport properties of La2NiO4

La₂NiO₄ compounds were prepared by a modified sol–gel auto-combustion method, which is a low-temperature combustion synthesis procedure using microwave-assisted sol–gel as precursors. The high-temperature transport properties of the samples were investigated. The band structure, total density of states (DOS), and partial density of states (PDOS) of low-temperature orthorhombic (Bmab) phase and high-temperature tetragonal (I4/mmm) phase for La₂NiO₄ were calculated in order to study the transport properties of the as-obtained samples.     

Electrical and optical characteristics of the InAs/InAs0.7Sb0.1P0.2 single heterojunction photodiodes for the spectral range 1.6-3.5 μm

The electrical end optical characteristics of InAs/InAs_0.7Sb_0.1P_0.2 heterojunctions were studied. The dark current mechanisms in the heterostructures were investigated at several temperatures. The experimental results shows that, the low temperature region the tunneling mechanism of the current flow dominates in both, forward and reverse biases. At high temperatures region and in the range of voltage from 0.1 V to 1 V, the reverse current was defined by diffusion mechanism.