Band Structure of Semiconductors

We present a simple theoretical analysis of the effective electron mass (EEM) at the Fermi level for III–V, ternary and quaternary materials, on the basis of a newly formulated electron energy spectra in the presence of light waves whose unperturbed energy band structures are defined by the three-band model of Kane The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings under different external conditions It has been observed that the unperturbed isotropic energy spectrum in the presence of light changes into an anisotropic dispersion relation with the energy-dependent mass anisotropy In the presence of light, the conduction band moves vertically upward and the band gap increases with the intensity and colours of light It has been found, taking n-InAs, n-InSb, n-Hg1−xCdxTe and n-In1−xGaxAsyP1−y lattice matched to InP as examples, that the EEM increases with increasing electron concentration, intensity and wavelength in various manners The strong dependence of the effective momentum mass (EMM) at the Fermi level on both the light intensity and wavelength reflects the direct signature of the light waves which is in contrast with the corresponding bulk specimens of the said materials in the absence of photo-excitation The rate of change is totally band-structure-dependent and is influenced by the presence of the different energy band constants The well known result for the EEM at the Fermi level for degenerate wide gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions, and this compatibility is the indirect test of our generalized formalism

http://iopscience.iop.org/article/10.1088/0031-8949/75/6/012/pdf

A simple theoretical analysis of the effective electron mass in III-V, ternary and quaternary materials in the presence of light waves

An accurate ab initio full potential linear muffin-tin orbital method has been used to investigate the structural, electronic and optical properties of BP, BAs and their (BP) n /(BAs) n superlattices (SLs). The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The calculated structural properties of BP and BAs compounds are in good agreement with available experimental and theoretical data. It is found that BP, BAs and their alloys exhibit an indirect fundamental band gap. The fundamental band gap decreases with increasing the number of monolayer n . The optical properties show that the static dielectric constant significantly decreases in superlattices compared to their binary compounds.

Electronic structure of (BP)n/(BAs)n (0 0 1) superlattices

We study the effects of a composition gradient and of a non-vanishing heat flux on the phase velocity of thermal waves along a graded system. We take into account non-local and non-linear effects by applying a generalized heat transport equation. We compare the results for high-frequency and low-frequency waves. For low frequency, we discuss the conditions in which thermal waves may propagate in Si x Ge 1 − x and ( Bi 1 − x Sb x ) 2 Te 3 systems. For high frequency, we discuss the influence of the relaxation of the flux of the heat flux on the heat wave propagation.

A thermodynamic model for heat transport and thermal wave propagation in graded systems

We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized analysis. The TPM has also been investigated in QWs of II-VI, IV-VI, stressed materials, n-GaP, p-PtSb2, n-GaSb, and bismuth on the basis of the appropriate carrier dispersion laws in the respective cases. It has been found, taking QWs of n-CdGeAs2, n-Cd3As2, n-InAs, n-InSb, n-GaAs, n-Hg1?xCdxTe, n-In1?xGaxAsyP1?y lattice-matched to InP, p-CdS, n-PbTe, n-PbSnTe, n-Pb1?xSnxSe, stressed n-InSb, n-GaP, p-PtSb2, n-GaSb, and bismuth as examples, that the respective TPM in the QWs of the aforementioned materials exhibits increasing quantum steps with the decreasing electron statistics with different numerical values, and the nature of the variations are totally band-structure-dependent. In CNTs, the TPM exhibits periodic oscillations with decreasing amplitudes for increasing electron statistics, and its nature is radically different as compared with the corresponding TPM of QWs since they depend exclusively on the respective band structures emphasizing the different signatures of the two entirely different one-dimensional nanostructured systems in various cases. The well-known expression of the TPM for wide gap materials has been obtained as a special case under certain limiting conditions, and this compatibility is an indirect test for our generalized formalism. In addition, we have suggested the experimental methods of determining the Einstein relation for the diffusivity-mobility ratio and the carrier contribution to the elastic constants for materials having arbitrary dispersion laws.

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Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field: Simplified theory and relative comparison

We study theoretically the thermoelectric power in the presence of a large magnetic field (TPM) in heavily doped III–V, II–VI, PbTe/PbSnTe, strained layer and HgTe/CdTe quantum dot superlattices (QDSLs) with graded structures on the basis of newly formulated electron energy spectra and compare the same with that of the constituent materials. It has been found, taking heavily doped GaAs/Ga1−xAlxAs, CdS/CdTe, PbTe/PbSnTe, InAs/GaSb and HgTe/CdTe QDSLs as examples, that the TPM increases with increasing inverse electron concentration and film thickness, respectively, in different oscillatory manners and the nature of oscillations is totally band structure dependent. We have also suggested the experimental methods of determining the Einstein relation for the diffusivity–mobility ratio, the Debye screening length and the electronic contribution to the elastic constants for materials having arbitrary dispersion laws.

Simple theoretical analysis of the thermoelectric power in quantum dot superlattices of non-parabolic heavily doped semiconductors with graded interfaces under strong magnetic field

Einstein relation in quantum wells and nipi structures of nonlinear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestion for an experimental determination

We study the Einstein relation for the diffusivity-to-mobility ratio (DMR) in carbon nanotubes (CNTs) and quantum wires (QWs) of non-linear optical and optoelectronic materials. The respective DMR in QWs exhibits increasing quantum steps with increasing electron statistics. In CNTs, the DMR exhibits periodic oscillations with increasing carrier degeneracy and the nature is radically different as compared with the corresponding DMR of QWs since they emphasize the different signatures of the two entirely different one dimensional nanostructured systems. In addition, we have suggested an experimental method of determining the DMR for CNTs and QWs having arbitrary dispersion laws.

Einstein Relation in Carbon Nanotubes and Quantum Wires of Nonlinear Optical, Optoelectronic and Related Materials:Simplified Theory, Relative Comparison and Suggestion for an Experimental Determination

A low loss, highly selective and miniaturized dual pass band filter for the wireless (WiMAX, WLAN) application is proposed in this paper. The filter is designed with Multimode resonators, constructed with Uniform Impedance Resonator (UIR) and multiple open stubs. Two different coupling schemes (electronic and magnetic) are observed for the said dual pass bands. A detail analysis about the dimension of the resonators, resonating conditions and frequency calculations are presented in this paper. The dual pass bands are achieved at 3.45 GHz and 5.4 GHz with minimum pass band insertion loss (|IL|) 0.1 and 0.18 dB and the pass band Fractional Band widths (FBW) 4% and 8% respectively. With proper optimizations, Transmission Zeros (TZ) are achieved on both sides of the dual pass bands and the spurious pass band are kept around -20dB level and hence good selectivity is achieved. The overall size of the filter is optimized for the best possible results in terms of Insertion Loss, Return Loss and selectivity, is found to be (24.2 x 21)mm = (0.28 x 0.24)λg = 0.06 λg2.

Dual Pass Band Filter using Quad Stub Loaded Uniform Impedance Resonator

A triple pass band filter is proposed for wireless applications. Four cross coupled Stepped Impedance Resonators are used for the purpose. Three pass bands at 2.4, 3.5 and 5.4 GHz are achieved. Minimum Insertion Loss of the three pass bands are 1.00, -0.52 and -0.92 dB respectively. The Return Loss in the said pass bands are -27,-21 and -22 dB. The overall size of the designed filter is 24.7 mm x 18 mm (0.19 $\lambda_{g}$ x 0.14 $\lambda_{g}$). The Defective Ground Surface is introduced in the design to reduce the spurious pass bands and hence to improve the pass band selectivity and stop band suppressions.

A. Neogi

Papers

Simple theoretical analysis of the thermoelectric power in quantum dot superlattices of non-parabolic heavily doped semiconductors with graded interfaces under strong magnetic field

Einstein relation in quantum wells and nipi structures of nonlinear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestion for an experimental determination

Einstein Relation in Carbon Nanotubes and Quantum Wires of Nonlinear Optical, Optoelectronic and Related Materials:Simplified Theory, Relative Comparison and Suggestion for an Experimental Determination

Dual Pass Band Filter using Quad Stub Loaded Uniform Impedance Resonator

Triple Band Filter with Cross Coupled SIR for Wireless Applications and Harmonic pass band Rejection with DGS