Dr Pengyuan Yang

Research Staff

Email:
Phone: Work: 01483 68 2214
Room no: 17 NC 00

Office hours

9:30-6:30

Further information

Biography

Pengyuan Yang graduated with a Beng in Electronic & Electrical Engineering from University of Surrey in 2004, and subsequently received his PhD in 2009 from the same department. During this period his main area of research involved modelling and fabrication of MIR waveguide in silicon substrate. He successfully demonstrated a freestanding silicon waveguide with air cladding by employing a next generation lithography technique called proton beam writing. In 2010, he joined in Ion Beam Centre at University of Surrey as a research fellow. Currently he is working on silicon emission technologies based on nanocrystals.

Research Interests

Silicon photonics, Proton beam writing, optoelectronics, ion implantation, silicon nanocrystals

Research Collaborations

University of Manchester, University College of London.

Publications

Journal articles

  • Crowe IF, Papachristodoulou N, Halsall MP, Hylton NP, Hulko O, Knights AP, Yang P, Gwilliam RM, Shah M, Kenyon AJ. (2013) 'Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation'. Journal of Applied Physics, 113 (2)

    Abstract

    We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb-centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth. © 2013 American Institute of Physics.

  • Yang P, Gwilliam RM, Crowe IF, Papachristodoulou N, Halsall MP, Hylton NP, Hulko O, Knights AP, Shah M, Kenyon AJ. (2013) 'Size limit on the phosphorous doped silicon nanocrystals for dopant activation'. Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms,

    Abstract

    We studied the photoluminescence spectra of silicon nanocrystals doped with and without phosphorus as a function of isothermal annealing time. Silicon nanocrystals were prepared by the implantation of 80 keV Si into a 500 nm SiO film to an areal density of 8 × 10 at/cm. Half of the samples were co-implanted with P at 80 keV to 5 × 10 at/cm. The photoluminescence of the annealed samples were photo-excited at wavelength of 405 nm. For short anneal times, when the nanocrystal size distribution has a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts to the red. Our results indicate the donor electron generation depends strongly on the nanocrystal size. We also found a critical limit above which it allows dopant activation. © 2013 Elsevier B.V. All rights reserved.

  • Halsall MP, Crowe IF, Southern R, Yang P, Gwilliam RM. (2012) 'Broadband near-infrared emission from bismuth doped silicon oxide films prepared by ion-implantation'. Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, , pp. 23-24.

    Abstract

    A series of Bismuth (Bi) doped silicon oxide layers were prepared by ion-implantation. All the samples exhibit strong room temperature near-infrared photoluminescence in the range 1.0μm-1.3μm which we assign to Bi related centres in the oxide matrix, similar to that reported previously for Bi doped oxides fabricated by alternative methods. The activation and sensitization of these luminescent centres was studied as a function of anneal temperature and co-doping with silicon (Si) and aluminium (Al). Comparision with Erbium doped films prepared in a similar way reveals comparable emission intensity from the Bi doped films. The even wider Bi-related luminescence makes this system very promising for use in on-chip, broadband lasers and amplifiers, particularly for use in telecommunications. © 2012 IEEE.

  • Thomson DJ, Reed GT, Knights AP, Yang PY, Gardes FY, Smith AJ, Litvinenko KL. (2010) 'Total Internal Reflection Optical Switch in SOI With Defect Engineered Barrier Region'. JOURNAL OF LIGHTWAVE TECHNOLOGY, 28 (17), pp. 2483-2491.
  • Milosevic MM, Matavulj PS, Yang PYY, Bagolini A, Mashanovich GZ. (2009) 'Rib waveguides for mid-infrared silicon photonics'. J OPT SOC AM B, 26 (9), pp. 1760-1766.

    Abstract

    Design rules for both single-mode and polarization-independent strained silicon-on-insulator rib waveguides at the wavelength of 3.39 mu m are presented for the first time to our knowledge. Waveguide geometries with different parameters, such as waveguide height, rib width, etch depth, top oxide cover thickness and sidewall angle, have been studied in order to investigate and define design rules that will make devices suitable for mid-IR applications. Chebyshev bivariate interpolation with a standard deviation of less than 1% has been used to represent the zero-birefringence surface. Experimental results for the upper cladding stress level have been used to determine the influence of top oxide cover thickness and different levels of upper cladding stress on waveguide characteristics. Finally, the polarization-insensitive and single-mode locus is presented for different waveguide heights. (C) 2009 Optical Society of America

  • Teo EJ, Bettiol AA, Yang P, Breese MBH, Xiong BQ, Mashanovich GZ, Headley WR, Reed GT. (2009) 'Fabrication of low-loss silicon-on-oxidized-porous-silicon strip waveguide using focused proton-beam irradiation'. OPT LETT, 34 (5), pp. 659-661.

    Abstract

    we have successfully fabricated low-loss silicon-on-oxidized-porous-silicon (SOPS) strip waveguides with high-index contrast using focused proton-beam irradiation and electrochemical etching. Smooth surface quality with rms roughness of 3.1 nm is achieved for a fluence of 1 x 10(15)/cm(2) after postoxidation treatment. Optical characterization at a wavelength of 1550 nm shows a loss of 1.1 +/- 0.4 dB/cm and 1.2 +/- 0.4 dB/cm in TE and TM polarization respectively, which we believe is the lowest reported loss for SOPS waveguides. This opens up new opportunities for all-silicon-based optoelectronics applications. (C) 2009 Optical Society of America

  • Yang PY, Stankovic S, Crnjanski J, Teo EJ, Thomson D, Bettiol AA, Breese MBH, Headley W, Giusca C, Reed GT, Mashanovich GZ. (2009) 'Silicon photonic waveguides for mid- and long-wave infrared region'. JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, London, ENGLAND: 20, pp. 159-163.

    Abstract

    Silicon photonics is experiencing a dramatic increase in interest due to emerging application areas and several high profile successes in device and technology development (Liu et al Nature 427:615, 2004; Rong et al Nature 433:725, 2005; Almeida et al Nature 431:1081, 2004). Conventional waveguides in silicon photonics are designed for the telecom wavelengths. However, mid- and long-wave infrared regions are interesting for several application areas including sensing, communications, signal processing, missile detection and imaging (Soref et al J Opt A Pure Appl Opt 8:840, 2006). The most popular waveguide platform in silicon photonics is the Silicon-On-Insulator (SOI) structure, in the form of either a strip or a rib waveguide. This material structure, however, is not suitable for longer wavelengths (except in the 2.9-3.6 mu m range) due to the absorption spectra of silicon dioxide (Soref et al J Opt A Pure Appl Opt 8:840, 2006). In this paper, we discuss the design and fabrication of two different waveguide structures, the freestanding (Yang et al Appl Phys Lett 90:241109, 2007) and hollow core waveguides (StankoviÄaut double dagger et al Proceedings of 51th Conference ETRAN, 2007). The former is suitable for long-wave infrared applications as it has an air cladding, whilst the latter is a candidate for sensing in the mid-wave infrared wavelength region.

  • Mashanovich GZ, Milosevic M, Matavulj P, Stankovic S, Timotijevic B, Yang PY, Teo EJ, Breese MBH, Bettiol AA, Reed GT. (2008) 'Silicon photonic waveguides for different wavelength regions'. SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 23 (6) Article number ARTN 064002
  • Teo EJ, Bettiol AA, Breese MBH, Yang P, Mashanovich GZ, Headley WR, Reed GT, Blackwood DJ. (2008) 'Three-dimensional control of optical waveguide fabrication in silicon'. OPT EXPRESS, 16 (2), pp. 573-578.

    Abstract

    In this paper, we report a direct-write technique for three-dimensional control of waveguide fabrication in silicon. Here, a focused beam of 250 keV protons is used to selectively slow down the rate of porous silicon formation during subsequent anodization, producing a silicon core surrounded by porous silicon cladding. The etch rate is found to depend on the irradiated dose, increasing the size of the core from 2.5 mu m to 3.5 mu m in width, and from 1.5 mu m to 2.6 mu m in height by increasing the dose by an order of magnitude. This ability to accurately control the waveguide profile with the ion dose at high spatial resolution provides a means of producing three-dimensional silicon waveguide tapers. Propagation losses of 6.7 dB/cm for TE and 6.8 dB/cm for TM polarization were measured in linear waveguides at the wavelength of 1550 nm. (C) 2008 Optical Society of America.

  • Mashanovich GZ, Stankovic S, Yang PY, Teo EJ, Dell'Olio F, Passaro VMN, Bettiol AA, Breese MBH, Reed GT. (2008) 'Silicon waveguides for the mid-infrared wavelength region'. Proceedings of SPIE - The International Society for Optical Engineering, 6898
  • Mashanovich GZ, Stankovic S, Yang PY, Teo EJ, Dell'Olio F, Passaro VMN, Bettiol AA, Breese MBH, Reed GT. (2008) 'Silicon waveguides for the mid-infrared wavelength region'. SILICON PHOTONICS III, San Jose, CA: 6898 Article number ARTN 68980T
  • Yang PY, Mashanovich GZ, Gomez-Morilla I, Headley WR, Reed GT, Teo EJ, Blackwood DJ, Breese MBH, Bettiol AA. (2007) 'Freestanding waveguides in silicon'. APPLIED PHYSICS LETTERS, 90 (24) Article number ARTN 241109
  • Headley WR, Reed GT, Mashanovich GZ, Timotijevic B, Gardes FY, Thomson D, Yang P, Teo E-J, Blackwood DJ, Breese MBH, Bettiol AA, Waugh P. (2007) 'Future prospects for silicon photonics'. PHOTONIC MATERIALS, DEVICES, AND APPLICATIONS II, Maspalomas, SPAIN: 6593 Article number ARTN 65931I
  • Reed GT, Yang PY, Headley WR, Waugh PM, Mashanovich GZ, Thomson D, Gwilliam RM, Teo EJ, Blackwood DJ, Breese MBH, Bettiol AA. (2007) 'Novel fabrication techniques for silicon photonics'. SILICON PHOTONICS II, San Jose, CA: 6477 Article number ARTN 64770E

Conference papers

  • Mashanovich GZ, Headley WR, Milosevic MM, Owens N, Teo EJ, Xiong BQ, Yang PY, Nedeljkovic M, Anguita J, Marko I, Hu Y. (2010) 'Waveguides for mid-infrared group IV photonics'. Proceedings of IEEE 7th International Conference on Group IV Photonics, Beijing, China: 7th IEEE GFP, pp. 374-376.

    Abstract

    In this paper we present preliminary work on group IV photonic waveguides that may be suitable for mid-infrared wavelengths. Fabrication and experimental results for two waveguide structures are given.

  • Teo EJ, Yang P, Xiong BQ, Breese MBH, Mashanovich GZ, Ow YS, Reed GT, Bettiol AA. (2010) 'Novel types of silicon waveguides fabricated using proton beam irradiation'. SPIE Proceedings of SPIE - The International Society for Optical Engineering, San Francisco, USA: Silicon Photonics V 7606

    Abstract

    In this work, we describe the use of a combination of proton beam irradiation and electrochemical etching to fabricate high index-contrast waveguides directly in silicon without the need for silicon-on-insulator substrate. Various types of waveguides with air or porous silicon cladding have been demonstrated. We show that porous silicon (PS) is a flexible cladding material due to the tunability of its refractive index and thickness. The Si/PS waveguide system also possesses better transmittance in the ranges of 1.2-9 and 23-200 μm, compared to Si/SiO2 waveguides. This is potentially important for mid and far-IR applications. Since it is compatible with conventional CMOS technology, this process can be used for fabrication of integrated optoelectronics circuits.

  • Teo EJ, Bettiol AA, Breese MBH, Yang PY, Mashanovich GZ, Headley WR, Reed GT, Blackwood DJ. (2008) 'An all-silicon channel waveguide fabricated using direct proton beam writing'. Proceedings of SPIE - The International Society for Optical Engineering, San Jose, USA: Silicon Photonics III 6898, pp. 68980Q.1-68980Q.7.

    Abstract

    We report a novel technique for the fabrication of an all-silicon channel waveguide using direct proton beam writing and subsequent electrochemical etching. A focused beam of high energy protons is used to selectively inhibit porous silicon formation in the irradiated regions. By over-etching beyond the ion range, the irradiated region becomes surrounded by porous silicon cladding. Waveguide characterization carried out at 1550 nm on the proton irradiated waveguide shows that the propagation losses improve significantly from 20±2 dB/cm to 9±2 dB/cm after vacuum annealing at 800°C for 1 hour.

  • Stankovic S, Milosevic M, Timotijevic B, Yang PY, Teo EJ, Crnjanski J, Matavulj P, Mashanovich GZ. (2007) 'Silicon photonic waveguides for near- and mid-infrared regions'. POLISH ACAD SCIENCES INST PHYSICS ACTA PHYSICA POLONICA A, Belgrade, SERBIA: International School and Conference on Optics and Optical Materials 112 (5), pp. 1019-1024.

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