Md. N. Islam

Publications (6)6.01 Total impact

• Source

  Available from: arxiv.org

  Article: Band edge discontinuities and carrier transport in c-Si/porous silicon heterojunctions

  Md. N. Islam, Sanjay K. Ram, Satyendra Kumar
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  ABSTRACT: We have prepared light emitting nanocrystalline porous silicon (PS) layers by electrochemical anodization of crystalline silicon (c-Si) wafer and characterized the c-Si/PS heterojunctions using temperature dependence of dark current-voltage (I-V) characteristics. The reverse bias I-V characteristics of c-Si/PS heterojunctions are found to behave like Schottky junctions where carrier transport is mainly governed by the carrier generation-recombination in the depletion region formed on the PS side. Fermi level of c-Si gets pinned to the defect levels at the interface resulting in ln(I) proportional to V^0.5. The barrier height in the reverse bias condition is shown to be equal to the band offset at the conduction band edges. An energy band diagram for the c-Si/PS heterojunction is proposed.
  09/2007;
• Source

  Available from: Pere Roca Cabarrocas

  Article: Elucidation of microstructure of single-phase microcrystalline silicon based on crystallite size distributions

  Sanjay K. Ram, Md. N. Islam, P. Roca i Cabarrocas, Satyendra Kumar
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  ABSTRACT: Highly crystallized undoped hydrogenated microcrystalline silicon films prepared using SiF4-H2 mixture plasma were investigated at various stages of growth employing different microstructural probes. Our self-consistent results elucidate various aspects of the evolution of film microstructure, compositional changes and variations in crystallite size distributions with film growth. Inclusion of a bimodal crystallite size distribution in microstructural data analysis leads to results that are corroborative with those obtained from other microstructural tools, and yields a more physically accurate and coherent description of microcrystalline silicon film microstructure.
  08/2007;
• Source

  Available from: Pere Roca Cabarrocas

  Article: Structural Determination of Nanocrystalline Si Films Using Ellipsometry and Raman Spectroscopy

  Sanjay K. Ram, Md. N. Islam, P. Roca i Cabarrocas, Satyendra Kumar
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  ABSTRACT: Single phase nano and micro crystalline silicon films deposited using SiF4/H2 plasma at different H2 dilution levels were studied at initial and terminal stages of film growth with spectroscopic ellipsometry (SE), Raman scattering (RS) and atomic force microscopy (AFM). The analysis of data obtained from SE elucidates the microstructural evolution with film growth in terms of the changes in crystallite sizes and their volume fractions, crystallite conglomeration and film morphology. The effect of H2 dilution on film microstructure and morphology, and the corroborative findings from AFM studies are discussed. Our SE results evince two distinct mean sizes of crystallites in the material after a certain stage of film growth. The analysis of Raman scattering data for such films has been done using a bimodal size distribution of crystallite grains, which yields more accurate and physically rational microstructural picture of the material. Comment: 5 pages, 4 figures, 1 table
  07/2007;
• Article: Influence of surface states on the photoluminescence from silicon nanostructures

  Md. N. Islam, Satyendra Kumar
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  ABSTRACT: We report a phenomenological model to analyze the room temperature photoluminescence (PL) spectra observed from silicon nanostructures. We have explicitly incorporated the effects of localized surface states along with quantum confinement effects to obtain an analytical expression for the photoluminescence spectra. Normal as well as log-normal crystallite size distributions are considered for PL intensity calculations. Experimental PL data on a variety of nanocystalline silicon structures with directly measured crystallite size distribution have been analyzed. Our model is able to deduce size distribution parameters from PL data that agree well with the experiments. © 2003 American Institute of Physics.
  Journal of Applied Physics 01/2003; 93(3):1753-1759. · 2.17 Impact Factor
• Article: Symmetry-forbidden Raman scattering from porous silicon quantum dots

  Md. N. Islam, R. N. Panda, A. Pradhan, Satyendra Kumar
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  ABSTRACT: We report on the observation of symmetry-forbidden Raman (SFR) scattering modes from porous silicon structures at room temperature. The intensity of SFR lines is significantly enhanced by optimizing the thickness of porous silicon layers attached to the c-Si substrates. X-ray diffraction analysis and scanning electron microscopy provided significant information on the structural orientation of PS layer to understand the symmetry violations in the Raman selection rules. A combination of various mechanisms such as crystallite size effects, lattice mismatch induced micromisorientations of crystal planes, and multiple reflections and refraction within the porous silicon nanostructures explains our results.
  Phys. Rev. B. 01/2002; 65(3).
• Article: Influence of crystallite size distribution on the micro-Raman analysis of porous Si

  Md. N. Islam, Satyendra Kumar
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  ABSTRACT: First-order Raman spectra from nanocrystalline semiconductors reflect the influence of crystallite sizes on the Raman shifts and line shapes. A Gaussian distribution in crystallite sizes is explicitly included to calculate the Raman spectra of porous silicon. Several porous-silicon samples were prepared using electrochemical anodization, and Raman as well as photoluminescence measurements were carried out on the same spots using a micro-Raman probe. The size distribution obtained from fitting the Raman data using our procedure is able to predict the photoluminescence accurately in the quantum-confinement models. © 2001 American Institute of Physics.
  Applied Physics Letters 02/2001; 78(6):715-717. · 3.84 Impact Factor