Browsing by Author "Dr. Muhammad Imran"

Now showing 1 - 2 of 2

Computational Study of Structural and Spectroscopic Properties of Doped ZnSe for IR LEDs
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2023) Rizwana Parveen; CIIT/SP22-RPH-029/LHR; Dr. Muhammad Imran; LHR TP 8789
ZnSe is a hard and intrinsic semiconductor material with a naturally occurring hexagonal or cubic structure. It is potential material for optical devices in the visible and infrared regions due to its large direct band gap of 2.7 eV and strong exciton binding energy. The band gap of ZnSe can be modified to an optimal value in order to properly implement this semiconductor's properties for a specific application. The present research work focuses to investigate the structural and electronic properties as well as absorption coefficient of Mn-doped ZnSe materials in cubic and hexagonal phases using CASTEP numerical coding. Optimized lattice constants are used to construct supercell 2×2×2 for cubic and 1×2×2 for hexagonal supercells to explore the effect of Mn-dopant on structural and optical behavior of ZnSe. The GGA-PBE functional with ultra-soft pseudo-potential for cubic and OTFG-ultrasoft pseudo potential for hexagonal configurations is used for non-spin-polarized calculations. Direct band gap of 0.372eV from cubic and 0.912eV from hexagonal are observed for pure ZnSe supercell, whereas the Fermi level resides between the conduction band and valence band. The energy gap 0.109eV, 0.183eV, and 0.129eV for cubic and energy gap 0.349eV, 0.078eV, 0.087eV for hexagonal structure are observed for one, two and three atoms Mn doped ZnSe which is decreased due to presence of Mn impurity atoms. The absorption spectral peak at 2.6×105 cm-1 for pure ZnSe and 1.28×105cm-1, 2×105 cm-1 and 1.96×105 cm-1 are observed on introducing Mn as dopant in ZnSn. Reflectivity, dielectric function, refractive index, conductivity and loss function are decreased with increase in the number of Mn-dopant atoms in ZnSe structure for both cubic and hexagonal phase. The calculated results showed interband absorption due to presence of Mn impurities
Study Of Copper Indium Gallium Selenide (CIGS) Solar Absorber Thin Film with Grading Bandgap
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2023) Muhammad Jawad Nasir; CIIT/SP22-RPH-003/LHR; Dr. Muhammad Imran; LHR TP 8775
High cost and low efficiency are key challenges facing the Photo voltaic solar industry, copper indium gallium selenide (CIGS) has emerged as a promising material for thin-film solar cells due to its high absorption coefficient, tunable bandgap, and efficient charge generation. However, further efficiency improvements are sought to make CIGS technology fully competitive in the renewable energy market which can be addressed by improvising the material properties and developing cost-effective large-scale fabrication routes. The optimization of bandgap in CIGS absorber layer can be achieved by introducing external dopant or changing the ratio of constituent elements. In this research work, variation in the energy band gap of the CIGS active layer is investigated by changing the indium to gallium ratio to enhance and improve the absorption spectral range using density functional theory in CASTEP numerical coding software. The electronic and optical properties are studied using CASTEP with different Ga concentration using GGA-PBE functional as exchange and correlation with kinetic cutoff energy of 880 eV and norm-conversing pseudopotential. Among all the under-investigation materials, CISe2 has shown the highest bandgap of 1.377eV. As the Ga is introduced in CISe2 structure, the band gap reduces until it reaches to 1.286eV for CI0.5G0.4Se2 and again increases for CI0.4G0.6Se2 to 1.333eV until it reaches 1.252eV for CGSe2 because of increase in the p states of gallium across the Fermi level and similar behavior of absorption co-efficient is observed. The maximum absorption is observed within ultra-violet region of solar spectrum.