Search

The structural, electronic, optical and thermoelectric properties of copper-based ternary chalcogenides ACuSe2 (A = Sc, Y and La) were investigated within the framework of the density functional theory (DFT). The electronic band structures and density of states exhibit that ScCuSe2 and YCuSe2 have the indirect band gaps, while LaCuSe2 displays a direct band gap-type transition. The band structure calculations agree well with other results in the literature. The optical behavior of the studied materials was analyzed in terms of dielectric functions, refractive index, extinction coefficient, absorption coefficient, optical conductivity, reflectivity and energy loss factor. The refractive indices increase to the maximum values of 4.4, 4 and 4.1 at the short infrared and visible wavelengths for ScCuSe2, YCuSe2 and LaCuSe2, respectively. Then, they decrease to get a value below 1.0 at the UV wavelengths. Moreover, the material response with temperature was investigated by Seebeck coefficient, figure of merit, specific heat capacity, power factor, thermal conductivity and susceptibility. The high Seebeck effect and large power factor values confirm the efficiency of these materials in thermoelectric energy converter technology. Among the three studied ternary materials, YCuSe2 has the highest value of dimensionless figure of merit of 0.45 at room temperature. These results would probably provide a new route to the experimentalists for the potential usage and applications of ScCuSe2, YCuSe2 and LaCuSe2 in thermoelectric and optoelectronic devices.

We report here the electronic band structure of nanostructure type II superlattice (SL) InAs(d1 = 21 A)/GaSb(d2 = 24 A) performed in the envelope function formalism. We calculated the energy E(d1), E(kz), E(kp) and the effective mass in the direction of growth kz and in plane kp of the SL. When the temperature increases, the band gap Eg decreases and the corresponding cutoff wavelength λc increases. We interpreted photoluminescence and transport measurements of Haugan et al. with an agreement in the calculated gaps. The computed density of states and Fermi energy position indicated that the sample is a p type semiconductor with a transition from bi-dimensional to tri-dimensional conductivity near 20 K. This sample is medium infrared detector (3.92 μm

We have investigated in the bands structure and the effective mass, respectively, along the growth axis and in the plane of InAs (d1=48.5Å)/GaSb(d2=21.5Å) type II superlattice (SL), performed in the envelop function formalism. We studied the semiconductor to semimetal transition and the evolutions of the optical band gap, Eg(Γ), as a function of d1, the valence band offset Λ and the temperature. In the range of 4.2–300 K, the corresponding cutoff wavelength ranging from 7.9 to 12.6 µm, which demonstrates that this sample can be used as a long wavelength infrared detector. The position of the Fermi level, EF = 512 meV, and the computed density of state indicates that this sample is a quasi-two-dimensional system and exhibits n type conductivity. Further, we calculated the transport scattering time and the velocity of electrons on the Fermi surface. These results were compared and discussed with the available data in the literature.

We have used the envelope function formalism to investigate the bands structure of LWIR type II SL InAs (d1 = 2. 18d2)/In0.25Ga0.75Sb(d2 = 21.5 Å). Thus, we extracted optical and transport parameters as the band gap, cut off wavelength, carriers effective mass, Fermi level and the density of state. Our results show that the higher optical cut-off wavelength can be achieved with smaller layer thicknesses. The semiconductor-semi metal transition was studied as a function of temperature. Our results permit us the interpretations of Hall and Shubnikov-de Haas effects. These results are in agreement with experimental results in literature and a guide for engineering infrared detectors.

We investigated here the GaAs(d1 = 184 A)/Al0.18Ga0.82As (d2 = 42 A) multiple quantum wells based on our enhanced numerical calculations in the envelope function formalism. We calculated the band structures and the effective mass mi* of charge carriers. When the well thickness d1 increases, the bandgap Eg decreases like m*. The calculated Fermi level energy and the density of states show n-type conductivity and a quasi-two-dimensional transport character. When the barrier thickness d2 increases the bandwidth decreases as a result of the weakening of interlayer tunnelling along the growth direction in the first Brillouin zone. We also interpreted theoretically the Shubnikov-de Haas and quantum Hall effects measurements reported by B. G. Tavares et al. These results are necessary for the design and engineering of multiple quantum wells infrared detectors.

We report here bands structure and the effective mass, in the direction of growth and in plan of HgTe (d 1 = 4.5 nm)/ CdTe(d 2 =4.8 nm) superlattice done in the envelope function formalism. We investigated Hall Effect with the help of the density of states and the Fermi level as a function of temperature. We found that temperature generated transitions from quasi bidimensional holes (Q2D) to three dimensional (3D) electrons and p type to n type conductivity respectively. When T increases, E g increases and the cut-off wavelength λ c decreases, with 5.06 μm c c 0.72 Cd 0.28 Te for application as infrared detector at 21.88 K. These results are a guide for the design of infrared nanostructures detectors.

In this paper, we investigated the band structure and quantum magneto transport properties of the In0.53Ga0.47As(d1=100Å)/InP(d2=70Å) type I multi quantum wells (MQWs) at low temperature. These studies were based on the envelope function and effective mass formalisms. We calculated the effect of d1, d2, the band valence offset and temperature on the band gap and the cut-off wavelength of detection. The result of the computed density of states and the position of Fermi level indicate that this sample is quasi two-dimensional system with n-type conductivity. The calculated evolution of the cutoff wavelength with temperature predicts this MQWs can be used as a short-infrared detector. Furthermore, we interpreted theoretically the photoluminescence, the Shubnikov de Haas (SdH) and quantum Hall effects observed by Pusep et al.