Hameed Naseem | University of Arkansas (original) (raw)

Papers by Hameed Naseem

Chemical vapor deposition is considered a promising method for synthesis of graphene films on dif... more Chemical vapor deposition is considered a promising method for synthesis of graphene films on different types of substrate utilizing transition metals such as Ni. However, synthesizing a single-layer graphene and controlling the quality of the graphene CVD film on Ni are very challenging due to the multiplicity of the CVD growth conditions. COMSOL Multiphysics is used to investigate the graphene CVD growth on Ni film and determine the main factors affecting graphene CVD synthesis. Our COMSOL model uses transport of diluted species, heat transfer in Ni thin film as well as deformed geometry. In this particular research, the number of the simulated graphene layers on Ni film is compared with experimental data.

$Research paper thumbnail of In situ analysis of aluminum enhanced crystallization of hydrogenated amorphous silicon (a-Si:H) using X-ray diffraction$

Thin Solid Films, 1999

Abstract Deposition of polysilicon at low temperatures is important for the low cost production o... more Abstract Deposition of polysilicon at low temperatures is important for the low cost production of electronic devices, especially solar cells and active matrix liquid crystal displays (AMLCD). In this paper in situ X-ray diffraction studies of aluminum enhanced crystallization of hydrogenated amorphous silicon (a-Si:H) at low temperatures is reported. Hydrogenated amorphous silicon films were deposited on oxidized silicon substrates. Aluminum was deposited on the a-Si:H using evaporation. X-ray diffraction analysis was done in an evacuated temperature controlled camera at a glancing angle of 5° using thin film optics. Growth in the 〈111〉 silicon peak was monitored while annealing the samples at 200, 225, 250 and 275°C. Results show that the area under the 〈111〉 silicon peak grows linearly with time. The rate of crystallization was found to be higher at higher temperatures. Al-induced crystallization was found to follow an Arrhenius type dependence. The activation energy for the thermally activated phenomenon controlling crystallization was calculated to be 1.1 eV. This is close to the reported activation energy of 1.2 eV for the diffusion of Al in a-Si:H.

Journal of Applied Physics, 2016

Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2... more Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2% have been systematically studied. Such diodes were based on Ge/GeSn/Ge double heterostructures (DHS) that were grown directly on a Si substrate via a chemical vapor deposition system. Both photoluminescence and electroluminescence spectra have been characterized at temperatures from 300 to 77 K. Based on our theoretical calculation, all GeSn alloys in this study are indirect bandgap materials. However, due to the small energy separation between direct and indirect bandgap, and the fact that radiative recombination rate greater than non-radiative, the emissions are mainly from the direct Γ-valley to valence band transitions. The electroluminescence emissions under current injection levels from 102 to 357 A/cm 2 were investigated at 300 K. The monotonic increase of the integrated electroluminescence intensity was observed for each sample. Moreover, the electronic band structures of the DHS were discussed. Despite the indirect GeSn bandgap owing to the compressive strain, type-I band alignment was achieved with the barrier heights ranging from 11 to 47 meV.

Journal of Applied Physics, 1994

Fluorinated a-SiN(x):H(0 less than or = x less than or = 0.19) alloys prepared using glow dischar... more Fluorinated a-SiN(x):H(0 less than or = x less than or = 0.19) alloys prepared using glow discharge decomposition of NF3 and SiH4 have been characterized using infrared absorption and the constant photocurrent method (CPM). The bonding configurations and the oscillator strengths of various bonds in these alloys have been obtained from the infrared-absorption spectra. The density of defects and their distribution in the band gap have been obtained without making any assumptions about the form of the distribution. It is found that in this composition range the main defect is the neutral silicon dangling bond and the concentration of charged dangling bonds is either too low or they are not present in these alloys. The possible role of fluorine in these alloys is also discussed.

2015 IEEE Summer Topicals Meeting Series (SUM), 2015

Characterization of GeSn edge-emitting LEDs has been conducted with Sn compositions up to 8%. Roo... more Characterization of GeSn edge-emitting LEDs has been conducted with Sn compositions up to 8%. Room temperature electroluminescence spectra and emission power were measured. A peak power of 50 mW was achieved with an 8%-Sn device.

Characterization of silicon nanowires grown horizontally through aluminum thin films was conducte... more Characterization of silicon nanowires grown horizontally through aluminum thin films was conducted. We show in our work that the fabrication process of these wires depends mainly on the thermally-activated silicon diffusion in-between the boundaries of aluminum grains. The diffusion of silicon through grain boundary is much lower than the grain bulk. Therefore, silicon starts to accumulate and form a wire shape structure along these grain boundaries. At 600�C, these accumulations form a continuous network of nanowires. The results are unique in the fact that these nanowires are pushed to grow horizontally instead of the more common vertical direction. The majority of obtained nanowires have a diameter of 75 nm and a length > 5 μm.

2015 IEEE 15th Mediterranean Microwave Symposium (MMS), 2015

Nanowires (NWs) solar cells have the potential to outperform the thin-film counterparts in terms ... more Nanowires (NWs) solar cells have the potential to outperform the thin-film counterparts in terms of optical absorptance. In this study a novel silicon nanowire (SiNW) array structure that has near-unity absorption spectrum is proposed. The design of the new SiNW array is based on inclusion of diverse radius nanowires with proper geometrical distribution in the array. The distribution of the NWs in a unit cell is inspired from the diamond lattice structure. The optical absorption is studied for a nanowire heterostructure consisting of a crystalline silicon core surrounded by a conformal shell of amorphous silicon. The proposed heterostructure arrays with multiple wire radii are simulated using the Ansoft's HFSS software package and shown to achieve ~38% efficiency enhancement improvement over a uniform periodic array. The new design shows significant enhancement of the absorption spectrum over the entire solar spectrum of interest with significant reduction of the amount of material. The enhanced optical properties of advocated silicon nanowire array indicate potential use in the design of a wide range of nanoscale semiconductor electro-optical devices, including photovoltaic solar cells.

$Research paper thumbnail of A Study of Stress In Microwave Plasma Chemical Vapor Deposited Diamond Films Using X-Ray Diffraction$

Chemical Vapor …, 1997

Residual stress in polycrystalline diamond films has been studied. Uniform polycrystalline diamon... more Residual stress in polycrystalline diamond films has been studied. Uniform polycrystalline diamond films were deposited on 3.0in. diameter silicon substrates in a microwave plasma chemical vapor deposition (MPCVD) system. The effects of CH4/H2 ratio, pressure, and power variation ...

2021 IEEE 48th Photovoltaic Specialists Conference (PVSC)

ABSTRACT Multi-junction solar cell efficiency gains due to GeSn and SiGeSn have already shown tha... more ABSTRACT Multi-junction solar cell efficiency gains due to GeSn and SiGeSn have already shown that a need exists for significant advancement in growing this material in a commercially available CVD chamber. Ge1−xSnx films have been grown via an Epsilon RPCVD single wafer CVD deposition tool on Si using a relaxed Ge buffer layer. The material and optical properties of these films have been characterized for various compositions. We present the characterization of strained Ge1−xSnx with x = 0.9 % to 7 % and photoluminescence of Ge1−xSnx grown via a commercial CVD reactor. This commercial growth accessibility shows that this ternary material should allow for further advancements in multi-junction photovoltaics using Si CMOS compatible processes.

Optical Materials Express

Journal of Electronic Materials, 2015

Optical properties of germanium tin (Ge 1Àx Sn x) alloys have been comprehensively studied with S... more Optical properties of germanium tin (Ge 1Àx Sn x) alloys have been comprehensively studied with Sn compositions from 0 (Ge) to 12%. Raman spectra of the GeSn samples with various Sn compositions were measured. The room temperature photoluminescence (PL) spectra show a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Temperature dependent PL shows the PL intensity variation along with the temperature change, which reveals the indirectness or directness of the bandgap of the material. As temperature decreases, the PL intensity decreases with Sn composition less than 8%, indicating the indirect bandgap Ge 1Àx Sn x ; while the PL intensity increases with Sn composition higher than 10%, implying the direct bandgap Ge 1Àx Sn x. Moreover, the PL study of n-doped samples shows bandgap narrowing compared to the unintentionally (Boron) doped thin film with similar Sn compositions due to the doping.

Optical Manufacturing and Testing II, 1997

ABSTRACT In quality control nondestructive techniques gain more and more importance. Holographic ... more ABSTRACT In quality control nondestructive techniques gain more and more importance. Holographic interferometry has the advantage of being very sensitive and can be used contactless for inspection of technical components. The interferogram contains fringes, whose pattern holds information about the surface deformation of a part subjected to the load. The load in case of deposited silicone oxide film is cased by stress produced different thermal expansion temperature coefficients film and silicone substrate. Change in stress in thin silicon dioxide films was observed using a high stability portable holographic interferometer using dimension stability test. Pattern recognition algorithm for synthesis of stress analyses map is reported. A stress relaxation phenomenon in this film thickness of 0.5 micrometers on Si wafer has been observed. Correlation of differential stress with initial flatness deviation of Si wafer has been discovered. The advantages of the proposed measuring technique and results are discussed.

Silicon Photonics X, 2015

ABSTRACT

MRS Proceedings, 2004

ABSTRACTCW Argon-ion laser initiated aluminum induced crystallization (AIC) of RF magnetron sputt... more ABSTRACTCW Argon-ion laser initiated aluminum induced crystallization (AIC) of RF magnetron sputtered amorphous silicon (a-Si) thin films has been investigated. It was found that lasers could be effectively used to initiate AIC process at very low threshold power densities. An argon-ion laser (λ=514.5 nm) was used to anneal Al/a-Si/glass structures with varying power densities ranging between 55 and 125 W/cm2 and exposure times ranging from 10 to 120 s. X-ray diffraction analysis showed the resulting films to be polycrystalline. The crystallization rate increased both with power density and exposure time. Environmental scanning electron microscopy (ESEM) analysis showed that the surface features change with increasing power density and irradiation time. A dendritic growth pattern was observed in the initial stages of interaction between the films. A strong crystalline Raman peak at around 520 cm-1 was observed in the Raman spectra of the crystallized samples.

2014 IEEE Photonics Conference, 2014

Japanese Journal of Applied Physics, 1991

We propose a new deposition process, hybrid-plasma CVD, to overcome the difference in decompositi... more We propose a new deposition process, hybrid-plasma CVD, to overcome the difference in decomposition of source gases. In this new process, Sill 4 and CH 4 are decomposed individually in a RF plasma and a microwave plasma, respectively, for the deposition of CH 4 hydrogenated amorphous silicon-carbon. Efficient decomposition of CH 4 by a microwave plasma reduces the excess hydrogenation of carbon atoms. Reactions in the hybrid-plasma CVD are investigated by quadrupole mass spectroscopy. Film structures are investigated by Fourier transform infrared absorption and X-ray photoelectron spectroscopy, and electrical properties are also examined. The films show low hydrogenation of the C atom compared to the films of glow discharge method. Moreover, the films with optical bandgap less than 2.2 eV show photoconductivities in the range of 10-5 S/cm.

$Research paper thumbnail of Transmission electron microscopy and X-ray diffraction studies of quantum wells$

Bulletin of Materials Science, 1999

The evolution of the microstructure of a granular Cu 80 Fe 10 Ni 10 (at%) melt spun ribbon is stu... more The evolution of the microstructure of a granular Cu 80 Fe 10 Ni 10 (at%) melt spun ribbon is studied by means of transmission electron microscopy (TEM), energy filtered transmission electron microscopy (EFTEM) and X-Ray Diffraction. This system is interesting since large giant magnetoresistance (GMR) values have been measured for this composition. We have shown the presence of two face-centered cubic phases, an (Fe,Ni)-rich phase and a Cu-rich phase. The lattice parameters of those two phases are rather close and no diffraction or elastic contrast acts to evidence the two phases in TEM bright field mode. With EFTEM imaging, we have shown the presence of a fine scale (Fe,Ni)-rich precipitation, inside the Cu-rich fcc matrix. The precipitates are 2-4 nm large in the as-spun state, and 4-6 nm large after an annealing treatment of 2 hours at 400°C. The lattice parameter of the Curich phase in the as-spun sample is 0.3608 nm, and that of the (Fe,Ni)-rich phase is 0.3610 nm. After a 24 hours treatment at 600°C, the mean diameter of the particle is 20 nm and the lattice parameter of the (Fe,Ni)-rich phase has decreased to 0.3600 nm while that of the Cu-rich phase has increased to 0.3613 nm, which is constistent with a segregation of Fe and Ni in the precipitates. The composition and volume fraction of the two phases measured for this annealed sample are in good agreement with the Thermocalc® predictions.