dr. V. Mohammadi

PhD student
Electronic Components, Technology and Materials (ECTM), Department of Microelectronics

PhD thesis (Mar 2015): Low temperature PureB technology for CMOS compatible photodetectors
Promotor: Lina Sarro, Albert Theuwissen


Vahid Mohammadi was born in Mashhad in 1981. He received his M.Sc. degrees in Electrical and Electronic Engineering from the University of Shiraz, Iran in 2009. During his MSc, he has been fabricated a pressure sensor based on a PZT thin film. In January 2011, he joined the Faculty of Electrical Engineering, Mathematics and Computer Science at Delft University of Technology, The Netherlands where he is currently working toward his Ph.D. degree in the Silicon Device Integration Group of Prof. Lis K. Nanver. His current research is focused on improving the current technology for VUV / low-energy electron (photo)detectors and imagers and to develop a novel PureB-layer deposition especially at lower temperatures (400C-450C) to implant this layer to the low-penetration beams applications such as VUV, EUV, low-energy-electrons detectors and x-ray radiation detector which are capable to integrate into the advanced CMOS processes.


  1. A doping-less junction-formation mechanism between n-silicon and an atomically thin boron layer
    V. Mohammadi; S. Nihtianov; C. Fang;
    Scientific Reports,
    Volume 7, Issue 1, 2017. cited By 0. DOI: 10.1038/s41598-017-13100-0
    Abstract: ... The interest in nanostructures of silicon and its dopants has significantly increased. We report the creation of an ultimately-shallow junction at the surface of n-type silicon with excellent electrical and optical characteristics made by depositing an atomically thin boron layer at a relatively low temperature where no doping of silicon is expected. The presented experimental results and simulations of the ab initio quantum mechanics molecular dynamics prove that the structure of this new type of junction differs from all other known rectifying junctions at this time. An analysis of the junction formation has led to the conclusion that the chemical interaction between the surface atoms of crystalline silicon and the first atomic layer of the as-deposited amorphous boron is the dominant factor leading to the formation of a depletion zone in the crystalline silicon which originates from the surface. The simulation results show a very strong electric field across the c-Si/a-B interface systems where the charge transfer occurs mainly from the interface Si atoms to the neighboring B atoms. This electric field appears to be responsible for the creation of a depletion zone in the n-silicon resulting in a rectifying junction-formation between the n-silicon and the atomically thin boron layer.


  2. Stability, local structure and electronic properties of borane radicals on the Si(100) 2x1:H surface: A first-principles study
    C.M. Fang; V. Mohammadi; S. Nihtianov; M.H.F. Sluiter;
    Computational Materials Science,
    Volume 140, Issue Supplement C, pp. 253 - 260, 2017. DOI: https://doi.org/10.1016/j.commatsci.2017.08.036
    Keywords: ... Borane deposition, H passivated Si(001) surface, PureB process, Ab initio calculations.

    Abstract: ... Abstract Deposition of a thin B layer via decomposition of B2H6 on Si (PureB process) produces B-Si junctions which exhibit unique electronic and optical properties. Here we present the results of our systematic first-principles study of BHn (n=0-3) radicals on Si(100)2x1:H surfaces, the initial stage of the PureB process. The calculations reveal an unexpectedly high stability of BH2 and BH3 radicals on the surface and a plausible atomic exchange mechanism of surface Si atoms with B atoms from absorbed BHn radicals. The calculations show strong local structural relaxation and reconstructions, as well as strong chemical bonding between the surface Si and the BHn radicals. Electronic structure calculations show various defect states in the energy gap of Si due to the BHn absorption. These results shed light on the initial stages of the complicated PureB process and also rationalize the unusual electronic, optical and electrical properties of the deposited Si surfaces.


  3. Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers
    V. Mohammadi; S. Nihtianov;
    AIP Advances,
    Volume 6, Issue 2, pp. 025103, 2016.

  4. Chemical Vapor Deposition - Recent Advances and Applications in Optical, Solar Cells and Solid State Devices
    V. Mohammadi; S. Nihtianov;
    S. Neralla (Ed.);
    InTech publisher, Chapter Low-Temperature, , pp. 137-157, 2016. ISBN 978-953-51-2573-0.

  5. Influence of the surface oxide content of a boron capping layer on UV photodetector performance
    V. Mohammadi; R.W.E. van de Kruijs; P.R. Rao; J.M. Sturm; S. Nihtianov;
    In Proc. of the International Conference on Sensing Technology,
    pp. 656-660, March 2016.

  6. Low temperature, 400 °C, pure boron deposition: A solution for integration of high-performance Si photodetectors and CMOS circuits
    V. Mohammadi; S. Nihtianov;
    In S Tadigadapa; J. Lee (Ed.), Proc. of the IEEE Sensors conference,
    IEEE, pp. 1-4, 2015. harvest.

  7. Surface oxide content examination of capping boron layers in UV photodetectors
    V. Mohammadi; P. Ramachandra Rao; R.W.E. van de Kruijs; S. Nihtianov;
    In SR Bank; D Jena (Ed.), Proc. of the 73rd Annual Device Research Conference,
    IEEE, pp. 73-74, 2015. harvest.

  8. Stability characterization of high-performance PureB Si-photodiodes under aggressive cleaning treatments in industrial applications
    V. Mohammadi; L. Shi; U. Kroth; C. Laubis; S. Nihtianov;
    In LG Franquelo; BM Wilamowski (Ed.), Proc. of the IEEE International Conference on Industrial Technology,
    IEEE, pp. 3370-3376, 2015. Harvest.

  9. Low temperature PureB technology for CMOS compatible photodetectors
    Vahid Mohammadi;
    PhD thesis, Delft University of Technology, 2015.

  10. Numerical gas flow and heat transfer simulation in the ASM Epsilon 2000 CVD reactor for Pure Boron deposition
    V. Mohammadi; S. Mohammadi; S. Ramesh; S. Nihtianov;
    Annual Journal of Electronics,
    Volume 8, pp. 28-31, 2014.

  11. Research Update: Reactively sputtered nanometer-thin ZrN film as a diffusion barrier between Al and boron layers for radiation detector applications
    Golshani, Negin; Mohammadi, V.; Schellevis, H.; Beenakker, C. I. M.; Ishihara, R.;
    APL Materials,
    Volume 2, Issue 10, pp. 100702, 2014.

  12. Robust UV/VUV/EUV PureB Photodiode Detector Technology with High CMOS Compatibility
    L.K. Nanver; L. Qi; V. Mohammadi; K.R.M. Mok; W.B. de Boer; N. Golshani; A. Sammak; T.L.M. Scholtes; A. Gottwald; U. Kroth; F. Scholze;
    Journal of Selected Topics in Quantum Electronics,
    Volume 20, Issue 6, pp. pp.1-11, 2014.

  13. Temperature Dependency of the Kinetics of PureB CVD Deposition over Patterned Si/SiO2 Surfaces
    V. Mohammadi; N. Golshani; K.R.C. Mok; W.B. de Boer; J. Derakhshandeh; L.K. Nanver;
    Microelectronic Engineering,
    Volume 125, pp. 45-50, 2014.

  14. Thickness evaluation of deposited pureb layers in micro-/millimeter-sized windows to Si
    Mohammadi, V; Ramesh, S; Nanver, LK;
    In Proceedings - 2014 IEEE International Conference on Microelectronic Test Structures,
    pp. 194-199, 2014.

  15. Local Loading Effect of The Pure-Boron-Layer Chemical-Vapor Depositions
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver;
    ECS Transactions,
    Volume 50, Issue 4, pp. 333-341, 2013. DOI 10.1149/05004.0333ecst.

  16. VUV/Low-Energy-Electron Si Photodiodes with Post-Metal 400�C PureB Deposition
    V. Mohammadi; L. Qi; N. Golshani; K. R. C. Mok; W. B. de Boer; A. Sammak; J. J. Derakhshandeh. van der Cingel; L. K. Nanver;
    IEEE Electron Device Letters,
    Volume 34, Issue 12, 2013. DOI 10.1109/LED.2013.2287221.

  17. Effects of Annealing on Chemical-Vapor Deposited PureB Layers
    K. R. C. Mok; A. H. G. Vlooswijk; V. Mohammadi; L. K. Nanver;
    ECS Journal of Solid State Science and Technology,
    Volume 2, Issue 9, pp. 413-417, 2013. DOI 10.1149/2.044309jss.

  18. A Simple Model describing the kinetic of CVD Deposition of Pure-Boron Layers from Diborane
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver and;
    ECS Transactions,
    Volume 45, Issue 31, pp. 57-65, 2013. DOI 10.1149/04531.0057ecst.

  19. Piezoelectric Pressure Sensor Based on Enhanced Thin-Film PZT Diaphragm Containing Nanocrystalline Powders
    V. Mohammadi;
    In F. Ebrahimi (Ed.), InTech-Piezoelectrisc Materials and Devices - Practice and Applications,
    Feb. 2013. ISBN 978-953-51-1045-3, DOI 10.5772/54755s.

  20. Investigation of the Issues Arising by Lowering the Deposition Temperature of the PureB-layer on Si/SiO2 Surfaces
    V. Mohammadi; N. Golshani; K.R.C. Mok; W.B. de Boer; J. Derakhshandeh; L.K. Nanver and;
    In ICT.OPEN,
    Eindhoven, The Netherlands, Nov. 2013.

  21. High-Ohmic Resistors using Nanometer-Thin Pure-Boron Chemical-Vapour-Deposited Layers
    N. Golshani; V. Mohammadi; S. Ramesh; L.K. Nanver and;
    In ESSDERC 2013,

  22. Temperature Dependency of the Kinetics of PureB CVD Deposition over Patterned Si/SiO2 Surfaces
    V. Mohammadi; N.Golshani; K.R.C. Mok; W.B. de Boer; J. Derakhshandeh; L.K. Nanver and;
    In E-MRS 2013 Fall Meeting 2013,
    Warsaw, Poland, Sep 2013.

  23. An Analytical Kinetic Model for Chemical-Vapor Deposition of Pure-Boron Layers from Diborane
    V. Mohammadi; W.B. de Boer; L.K. Nanver and;
    Journal of Applied Physics,
    Volume 112, 2012. DOI 10.1063/1.4767328.

  24. Pattern dependency and loading effect of pure-boron-layer chemical-vapor deposition
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver;
    ECS Journal of Solid State Science and Technology,
    Volume 1, Issue 1, pp. Q16-Q20, 2012. DOI 10.1149/2.024201jss.

  25. Temperature dependence of chemical-vapor deposition of pure boron layers from diborane
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver;
    Applied Physics Letters,
    Volume 101, Issue 11, pp. 1-4, 2012. DOI 10.1063/1.4752109.

  26. Impact of the Process and Chamber Parameters on CVD Deposition of PureB layer
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver;
    In ICT.OPEN: Micro technology and micro devices (SAFE 2012),
    Rotterdam, The Netherlands, Oct. 2012.

  27. Pattern dependency of pure-boron-layer chemical-vapor depositions
    V. Mohammadi; W.B. de Boer; T.L.M. Scholtes; L.K. Nanver;
    In 221st ECS Meeting: ECS Transactions,
    Seattle, Washington, pp. 39-48, May 2012. DOI 10.1149/1.3700937.

  28. Pure dopant deposition of B and Ga for ultrashallow junctions in Si-based devices
    L.K. Nanver; A. Sammak; V. Mohammadi; K.R.C. Mok; L. Qi; A. Sakic; N. Golshani; J. Derakhshandeh; T.M.L. Scholtes; W.D. de Boer;
    In ECS Trans. 2012: 27th Symposium on Microelectronics Technology and Devices (SBMicro2012),
    Brazil, Brasilia, pp. 25-33, Aug. 2012. DOI 10.1149/04901.0025ecst.

  29. Applications of PureB and PureGaB ultrashallow junction technologies
    L.K. Nanver; A. _akic; V. Mohammadi; J. Derakhshandeh; K.R.C. Mok; L. Qi; N. Golshani; T.M.L. Scholtes; W.B. de Boer;
    In 2012 IEEE 11th International Conference on Solid-State and Integrated Circuit Technology (ICSCT 2012),
    Xi'an, pp. 303-306., Oct. 2012.

  30. Low-pressure chemical vapor deposition of pureB layers on silicon for p+n junction formation
    K.R.C. Mok; V. Mohammadi; L.K. Nanver; W.D. de Boer; A.H.G. Vlooswijk;
    In 12th International Workshop on Junction Technology (IWJT 2012),
    Shanghai, China, pp. 113-116, May 2012. DOI 10.1109/IWJT.2012.6212822.

  31. On the uniformity of pure-boron-layer depositions
    V. Mohammadi; W.D. de Boer; T.L.M. Scholtes; A. Sakic; C. Heerkens; L.K. Nanver;
    In Proc. ICT.OPEN: Micro technology and micro devices (SAFE 2011),
    Veldhoven, The Netherlands, pp. 73-75, Nov. 2011.

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Last updated: 21 Jul 2020

Vahid Mohammadi

  • Left in 2015
  • Now: ASML