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In this research work, the tungsten diselenide (WSe2)-based thin-film solar cell with a copper thiocyanate (CuSCN) hole transport layer (HTL) has been designed and studied by using the Solar Cell Capacitance Simulator in One Dimension software program (SCAPS-1D). A comparative numerical study between Al/ITO/CdS/WSe2/Ni and Al/ITO/CdS/WSe2/CuSCN/Ni has been done. The SCAPS-1D simulator has been utilized to investigate photovoltaic parameters such as open circuit voltage, short-circuit current density, fill-factor, power conversion efficiency and quantum efficiency of heterojunction solar cell due to the variation of thickness, doping density, bulk defect density, defect density at buffer/absorber and absorber/HTL interfaces, operating temperature, band alignment and back surface recombination velocity. The conversion efficiency of 17.33% has been determined for the WSe2 solar cell without HTL. On the contrary, the efficiency of the proposed solar cell with CuSCN HTL has been found to be 24.20% at the optimal device structure. These numerical findings of the present study may therefore provide an intuitive approach to fabricate an economically feasible and highly efficient WSe2-based heterojunction thin-film solar cell.

Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform generation in wideband transmission. it's a superior technology for the high-speed rate of wired and wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G networks & tactical communication. The OFDM has many advantages over other techniques like its high capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping (SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLM- PTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate (BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the proposed scheme is more complex than the prevailing techniques.

Antimony (Sb) chalcogenides such as antimony selenide (Sb

Photonic crystal fiber-based heptagonal cladding with the elliptical rotated-Hexa core is reported in the terahertz waveguide for the applications of communication area in this paper. By utilizing the photonic crystal fiber concept, all numerical results have been obtained by the finite element method with perfectly matched layers based on the COMSOL Multiphysics computer software tool. This H-PCF fiber shows a low effective material loss of 0.0076 cm−1, with a larger effective area of 5.95 × 10–8 m2, power flows within the core area of 90%, confinement loss of 3.35 × 10–16 cm−1, and scattering loss of 1.24 × 10–10 cm−1 at 1 THz. Besides, other optical properties like confinement loss, scattering loss, power fraction, V-parameter, and effective area have also been considered briefly. So, it is expected that the mentioned H-PCF structure-based waveguide will significantly improve many kinds of communication fields of the THz technology.

In this study, we examined the E− band luminescence of a GaAs:N δ-doped superlattice (SL) grown by metal organic vapor phase epitaxy with 0.15% nitrogen (N) using two-wavelength excited photoluminescence. It was observed that the photoluminescence (PL) intensity of the low-energy peak (P2) at 1.38 eV of the E− band was quenched larger compared to the high-energy peak (P1) at 1.41 eV. This was due to the superposition of below-gap excitation (BGE) light of energy 0.95 eV over the above-gap excitation light of energy 1.45 eV on the SL structure at a fixed temperature of 12 K. On the other hand, at higher temperatures, the PL intensity of the high-energy peak P1 was quenched higher compared to the low-energy peak P2 without any addition of the BGE light. We interpreted the experimental results by considering the carrier recombination (CR) model and concluded that the observed PL spectral and intensity change of the E− band emission due to BGE does not result from the thermal activation, but from the optical excitation among the E− band, conduction band, and CR levels in GaAs:N δ-doped structure. We concluded that to achieve high-efficiency intermediate band-type solar cells, it is essential to understand the CR mechanism through CR levels by determining their origin and eliminating them from the material.

In the present study, the performance parameters of GaAsN dilute nitride-based semiconductor solar cell with and without AlGaAs blocking layers have been investigated in detail by Solar Cell Capacitance Simulator in one dimensional software program (SCAPS-1D). The thickness of absorber, buffer, and blocking layers are varied to achieve the improvement of open circuit voltage, short circuit current, fill factor, efficiency and also to optimize the device structure. The impact of doping and defect densities on the solar cell performance parameters have been analyzed minutely inside the absorber, buffer, and blocking layers. The solar cell thermal stability parameters are also investigated in the temperature region from 273K to 373K. The efficiency of 43.90% and 40.05% are obtained from the proposed solar cells with and without AlGaAs blocking layer, respectively. The present findings may provide insightful approach for fabricating feasible, cost effective, and efficient dilute nitride solar cell.

This research article demonstrates a good simulation result for identifying and detecting various industrial chemicals in a Terahertz (THz) waveguide with a new heptagonal, five layers of heptagonal photonic fiber elliptic form, heptagonal cladding shape (H-PCF). COMSOL 4.2 software based on finite element (FEM) methods and perfectly matched layers check our composition (PML). The different chemicals are also differentiated and identified by each other in different parameters H-PCF fibers show a high relative sensitivity of ethanol of approximately 86.50 percent after numerical analysis, Benzene around 89.35%, and water around 85.15% at a frequency of around 0.7 THz. In our experiment, we obtained very low confinement losses at 1 terahertz (THz) such as 5.95 × 10−08 dB/m for Ethanol 6.67 × 10−08 dB/m for Benzene, and 5.80 × 10−08 dB/m for water. Regarding these results, we can strongly recommend that our proposed heptagonal photonic crystal fiber (H-PCF) will be more congenial in biomedical, bio-medicine, and industrial areas for the identification and detection of various types of chemicals with the help of a THz waveguide.

Nonradiative recombination (NRR) centers in n-type GaN samples grown by MOCVD technique on a LT-GaN buffer layer and aAlN buffer layer have been studied by two wavelength excited photoluminescence (TWEPL). The near band-edge photoluminescence (PL) intensity decreases due to the superposition of below-gap excitation (BGE) light of energies 0.93, 1.17 and 1.27 eV over above-gap excitation (AGE) light of energy 4.66 eV. The decrease in PL intensity due to the addition of the BGE has been explained by a two levels recombination model based on SRH statistics. It indicates the presence of a pair of NRR centers in both samples, which are activated by the BGE. The degree of quenching in PL intensity for the sample grown on LT-GaN buffer layer is stronger than the sample grown on AlN buffer layer for all BGE sources. This result implies that the use of the AlN buffer layer is more effective for reducing the NRR centers in n-GaN layers than the LT-GaN buffer layer. The dependence of PL quenching on the AGE density, the BGE density and temperature has been also investigated. The NRR parameters have been quantitatively determined by solving rate equations and fitting the simulated results with the experimental data.

博士の専攻分野の名称 : 博士(学術)学位授与年月日 : 平成30年9月21日

Nonradiative recombination (NRR) centers in GaAs:N $\delta$-doped superlattices (SLs) grown by molecular beam epitaxy (MBE) has been investigated by two-wavelength excited photoluminescence (TWEPL) method for conduction band scheme. The PL intensity of $E_{-}$ band of the samples with lower nitrogen (N) concentration (0.317% N) initially increases after addition of below-gap excitation (BGE) light over above-gap excitation (AGE) light and then quenches at higher BGE density and energy, while that of GaAs (e-A°) emission of GaAs layers decreases monotonically. For sample with higher N concentration (1.18% N) both the $E _{-}$ band and GaAs (e-A°) emission decreases monotonically with enhancing BGE density and degree of decreasing of PL intensity is higher compared to the low N concentration sample. The quenching of PL intensity indicates the existence of NRR centers in GaAs layers and GaAs:N $\delta$-doped SL region. The recombination models have been proposed for explaining the results from the experiments.

Comparative study on nonradiative recombination (NRR) centers in InAs/GaAs quantum dot (QD) structure generated by 3 MeV proton irradiation is performed by two wavelength excited photoluminescence (TWEPL). The above-gap excitation (AGE) source of 2.33 eV or 1.26 eV is used to excite GaAs host material or InAs QDs, respectively. The QD PL intensity decreased after irradiation of below-gap excitation (BGE) of 0.75 eV over AGE, indicating a pair of NRR centers activated. The proton irradiation at fluence of $7\times 10^{11}\mathrm{cm}^{-2}$ reduces the NRR density, while that of ${4\times 10^{12}\mathrm{cm}^{-2}}$ increases it. Defect formation, carrier injection and their fluence dependence explain experimental results.

Nonradiative recombination (NRR) centers in as-grown and proton-irradiated InAs/GaAs quantum dot (QD) structures have been studied by two-wavelength-excited photoluminescence (PL). The PL intensity quenching of GaAs and QD emissions due to the addition of a below-gap excitation light of 0.80 eV energy indicates the presence of defect levels acting as NRR centers. The method enables us to discuss the distribution of NRR centers in GaAs and/or InAs QD regions by selecting either conduction band excitation (2.33 eV) or intermediate band excitation (1.27 eV). We have found that the densities of NRR centers in GaAs layers and the effect of quenching on GaAs emissions increase monotonically with increasing proton irradiation fluence. The QD emission intensity, however, increases at a moderate fluence of 7 × 1011 protons/cm2 owing to the defect-assisted trapping of electrons into QDs. Further incorporation of NRR centers after 4 × 1012 protons/cm2 fluence quenches the QD-PL intensity below that of an unirradiated sample.

We use two-wavelength-excited photoluminescence (PL) to investigate nonradiative recombination (NRR) centers in GaAs:N δ-doped superlattice (SL) structures grown by molecular beam epitaxy. The change in photoluminescence (PL) intensity due to the superposition of below-gap excitation at energies of 0.75, 0.80, 0.92, and 0.95 eV and above-gap excitation at energies of 1.69 or 1.45 eV into the GaAs conduction band and the E− band implies the presence of NRR centers inside the GaAs:N δ-doped SL and/or GaAs layers. The change in PL intensity as a function of the photon number density of below-gap excitation is examined for both bands, which enables us to determine the distribution of NRR centers inside the GaAs:N δ-doped SL and GaAs layers. We propose recombination models to explain the experimental results. Defect-related parameters that give a qualitative insight into the samples are investigated systematically by fitting the rate equations to the experimental data.

In this paper, we study the effect of various concatenated forward error correction (FEC) codes on the performance of a wireless orthogonal frequency division multiplexing (OFDM) system. In FEC concatenated channel code, the OFDM system incorporates Reed-Solomon (RS) encoder of (255,239,8), Cyclic Encoder of (15,11), Bose-Chadhuri-Hocquenghem (BCH) encoder of (127,64) with Convolution encoder of 2/3 and frac34-rated codes under different combinations of digital modulation (QPSK, 8PSK, 32-QAM and 64-QAM). The simulation study is made with the development of a computer program written in Matlab source code on the processing of recorded audio signal under additive white Gaussian noise (AWGN) channel. The simulation results of estimated Bit error rate (BER) show that the implementation of concatenated RS(255,239,8) code with frac34-rated Convolutional code under QPSK modulation technique is highly effective to combat inherent interference in the communication system. Due to constraint in data handling capability of the Matlab editor, a segment of the recorded audio signal is used for analysis. The transmitted audio message is found to have retrieved effectively under noisy situation.