In the last 30 days

• Open/close Optimization of grid design for solar cells

  Liu Wen et al 2010 J. Semicond. 31 014006 Tag this article

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  By theoretical simulation of two grid patterns that are often used in concentrator solar cells, we give a detailed and comprehensive analysis of the influence of the metal grid dimension and various losses directly associated with it during optimization of grid design. Furthermore, we also perform the simulation under different concentrator factors, making the optimization of the front contact grid for solar cells complete.

• Open/close Influence of window layer thickness on double layer antireflection coating for triple junction solar cells

  Wang Lijuan (王莉娟) et al 2011 J. Semicond. 32 066001 Tag this article

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  The optimization of a SiO ₂/TiO ₂, SiO ₂/ZnS double layer antireflection coating (ARC) on Ga _0.5In _0.5P/In _0.02Ga _0.98As/Ge solar cells for terrestrial application is discussed. The Al _0.5In _0.5P window layer thickness is also taken into consideration. It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.

• Open/close Fabrication and characteristics of a 4H-SiC junction barrier Schottky diode

  Chen Fengping (陈丰平) et al 2011 J. Semicond. 32 064003 Tag this article

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  4H-SiC junction barrier Schottky (JBS) diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently, and the other is processed by depositing a Schottky metal multi-layer on the whole anode. The reverse performances are compared to find the influences of these factors. The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage, and with independent P-type ohmic contact manufacturing, the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore, the P-type ohmic contact is studied in this work.

• Open/close Physical properties of sprayed antimony doped tin oxide thin films: The role of thickness

  A. R. Babar et al 2011 J. Semicond. 32 053001 Tag this article

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  Transparent conducting antimony doped tin oxide (Sb:SnO ₂) thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the (211) and (112) planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb:SnO ₂ thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3d _5/2 for all samples shows the Sn ⁴⁺ bonding state from SnO ₂. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb ⁵⁺ ions. The film deposited with 20 cc solution shows 70 % transmittance at 550 nm leading to the highest figure of merit (2.11 × 10 ⁻³Ω ⁻¹). The resistivity and carrier concentration vary over 1.22 × 10 ⁻³ to 0.89 × 10 ⁻³Ω·cm and 5.19 × 10 ²⁰ to 8.52 × 10 ²⁰ cm ⁻³, respectively.

• Open/close Physical properties of hematite α-Fe₂O₃ thin films: application to photoelectrochemical solar cells

  S. S. Shinde et al 2011 J. Semicond. 32 013001 Tag this article

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  The physical properties and photoelectrochemical characterization of aluminium doped hematite α-Fe ₂O ₃, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (III) oxide thin films synthesized by a spray pyrolysis technique reveals an oxygen deficiency, and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films show the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20–40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to a blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films, AC conductivity is measured. The conduction occurs by small polaron hopping through mixed valences Fe ^2+/3+ with an electron mobility 300 K of 1.08 cm ²/(V·s). The α-Fe ₂O ₃ exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as a photoanode for various electrolytes using white light to obtain I — V characteristics. The Al-doped hematite exhibited a higher photocurrent response when compared with undoped films achieving a power conversion efficiency of 2.37% at 10 at % Al:Fe ₂O ₃ thin films along with fill factor 0.38 in NaOH electrolyte. The flat band potential V _fb (−0.87 V _SCE) is determined by extrapolating the linear part to C ⁻² = 0 and the slope of the Mott-Schottky plot.

• Open/close Approximate graphical method of solving Fermi level and majority carrier density of semiconductors with multiple donors and multiple acceptors

  Ken K. Chin 2011 J. Semicond. 32 062001 Tag this article

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  We present a generic approximate graphical method for determining the equilibrium Fermi level and majority carrier density of a semiconductor with multiple donors and multiple acceptors compensating each other. Simple and easy-to-follow procedures of the graphical method are described. By graphically plotting two wrapping step functions facing each other, one for the positive hole-ionized donor and one for the negative electron-ionized acceptor, we have the crossing point that renders the Fermi level and majority carrier density. Using the graphical method, new equations are derived, such as the carrier compensation proportional to N _A/ N _D, not the widely quoted N _A — N _D. Visual insight is offered to view not only the result of graphic determination of Fermi level and majority carrier density but also the dominant and critical pair of donors and acceptors in compensation. The graphical method presented in this work will help to guide the design, adjustment, and improvement of the multiply doped semiconductors. Comparison of this approximate graphical method with previous work on compensation, and with some experimental results, is made. Future work in the field is proposed.

• Open/close Optical and electrical properties of porous silicon layer formed on the textured surface by electrochemical etching

  Ou Weiying (欧伟英) et al 2011 J. Semicond. 32 056002 Tag this article

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  Porous silicon (PS) layers were formed on textured crystalline silicon by electrochemical etching in HF-based electrolyte. Optical and electrical properties of the TMAH textured surfaces with PS formation are studied. Moreover, the influences of the initial structures and the anodizing time on the optical and electrical properties of the surfaces after PS formation are investigated. The results show that the TMAH textured surfaces with PS formation present a dramatic decrease in reflectance. The longer the anodizing time is, the lower the reflectance. Moreover, an initial surface with bigger pyramids achieved lower reflectance in a short wavelength range. A minimum reflectance of 3.86% at 460 nm is achieved for a short anodizing time of 2 min. Furthermore, the reflectance spectrum of the sample, which was etched in 3 vol.% TMAH for 25 min and then anodized for 20 min, is extremely flat and lies between 3.67% and 6.15% in the wavelength range from 400 to 1040 nm. In addition, for a short anodizing time, a slight increase in the effective carrier lifetime is observed. Our results indicate that PS layers formed on a TMAH textured surface for a short anodization treatment can be used as both broadband antireflection coatings and passivation layers for the application in solar cells.

• Open/close First-principles study on transport properties of zigzag graphene nanoribbon with different spin-configurations

  An Liping (安丽萍) and Liu Nianhua (刘念华) 2011 J. Semicond. 32 052001 Tag this article

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  The current—voltage (I—V) characteristics and the transmission spectra of zigzag graphene nanoribbon with different spin-configurations are investigated by using first-principles calculations. It is shown that the I—V curves and transmission spectra strongly depend on the spin-configurations of the two sides of the ribbon. For the spin-parallel configuration structure, the curve is linear under lower bias voltage; for the spin-antiparallel configuration structure, there is a strong spin-polarization-dependent transmission which implies that the ribbon can be used as a spin filter; while for other spin-configuration structures, the curve has the characteristics of a semiconductor. It is found that there is a large magneto-resistance (MR) when the bias voltage is small. The impurity in the central scattering region significantly influences the spin-dependent current and the spin filter efficiency, which may lead the large MR to disappear.

• Open/close Surface reconstructions and reflection high-energy electron diffraction intensity oscillations during homoepitaxial growth on nonmisoriented GaAs(111)B by MBE

  Yang Ruixia et al 2010 J. Semicond. 31 113001 Tag this article

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  The growth by molecular beam epitaxy of high quality GaAs epilayers on nonmisoriented GaAs(111)B substrates is reported. Growth control of the GaAs epilayers is achieved via in situ, realtime measurement of the specular beam intensity of reflection high-energy electron diffraction (RHEED). Static surface phase maps of GaAs(111)B have been generated for a variety of incident As flux and substrate temperature conditions. The dependence of GaAs(111)B surface reconstruction phases on growth parameters is discussed. The surface reconstruction is identified to be the optimum starting surface for the latter growth of mirror-smooth epilayers. Regimes of growth conditions are optimized in terms of the static surface phase diagram and the temporal RHEED intensity oscillations.

• Open/close GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

  Li Zaijin et al 2010 J. Semicond. 31 036002 Tag this article

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  A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH ₄OH:H ₂O ₂:H ₂O = 1:1:10 solution and HCl: H ₂O ₂:H ₂O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH ₄OH:H ₂O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology.