P.G. Han

City University of Hong Kong, Chiu-lung, Kowloon City, Hong Kong

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Publications (21)9.45 Total impact

  • Hei Wong, P.G. Han, M.C. Poon
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    ABSTRACT: We conducted a series of experiments on porous silicon (PS) and porous polysilicon (PPS) to investigate the origins of photoluminescence in these materials. A study of the effects of surface layer plasma etching, for several different durations, on the as-anodized samples was conducted. For the photoluminescence (PL) study, results show that the intensity decreases rapidly, but the peak locations remain fairly unchanged, as the surface etching proceeds. In addition, only one band centered at around 680 nm (1.82 eV) is found in the PS samples whereas two bands, centered at 400 nm (3.1 eV) and 680 nm, are found in the PPS samples. The 400 nm peak disappears when the surface oxide layer was completely removed. These results could not be explained with the quantum confinement model of silicon nano structures. We ascribe these PL effects to the radiative centers in the surface oxide layer. Fourier transform infrared (FTIR) measurements on these samples further reveal that the PL peak at 680 nm correlates well with the NBOHCs (non-bridged oxide hole centers or ≡-SiO·) and the 3.1 eV peak can also be attributed to the oxygen vacancy (≡Si-Si≡) in the surface silicon oxide layer.
    Devices, Circuits and Systems, 2002. Proceedings of the Fourth IEEE International Caracas Conference on; 02/2002
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    ABSTRACT: By etching back the as-oxidized polysilicon using reactive ion, a uniform porous polysilicon structure with significant enhancement of photoluminescence (PL) intensity was formed. We further found that the PL peak is centered at around 680 nm and is independent on the porosities or sizes of Si micropores. These results indicate the light emission in the samples should not be a consequence of the quantum confinement. Instead, the 680-nm peak should be due to the non-bridged oxide hole centers (SiO·) at the oxidized grain boundaries of the polysilicon.
    Microelectronics Reliability 01/2002; 42:929-933. · 1.14 Impact Factor
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    ABSTRACT: Porous silicon (PS) offers many potential advantages for the realization of optoelectronic applications. However, the electrochemical anodizing method used to fabricate porous silicon has resulted in many undesirable sub-effects, such as impurities due to reactive residents, nonstabilized surface, nonuniform pore structure, and high film stress, leading to contamination of conventional VLSI processes. In this paper, we report a new dry etching method to produce the light-emitting PS. The formation mechanism of this film is proposed. Using the samples prepared with this new method, results demonstrate that the luminescence in this film does not have strong correlation with size of the nano-structures and we therefore suggest that the luminescence in this film is not due to the quantum confinement effects
    Electron Devices Meeting, 2001. Proceedings. 2001 IEEE Hong Kong; 02/2001
  • P.G Han, H Wong, M.C Poon
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    ABSTRACT: Porous silicon (PS) used as a sensing material for micro-sensors has attracted a lot of attention in recent years. Owing to the large surface area (∼200 m2 cm−3) and high chemical activity, porous silicon would be a good choice for gas sensor applications. In this paper, a resistivity sensor using porous polycrystalline silicon (PPS) thin films was fabricated by anodization and standard lithographic technique. Analytical measurements on the sample reveal that these sensing porous poly-Si films consist of many pores with a diameter of ∼100 nm. A high sensitivity to ambient pressure and ethanol vapor was observed. The sensitivity and stability of PPS gas sensor have been characterized and analyzed as a function of gas concentration and storing duration. In particular, we will discuss the mechanism of the interaction between the surface state of PPS and ambient gases in detail. Suggestions to further improve the sensor stability will also be proposed.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2001; · 2.11 Impact Factor
  • Hei Wong, P. G. Han, M. C. Poon, Y. Gao
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    ABSTRACT: The surface properties of porous poly-Si (PPS) have profound effects on the characteristics of optoelectronic devices and PPS-based gas and bio-chemical sensors. In this work, the effects of plasma dry etching on the surface structures and optical characteristics of PPS film are investigated. Experimental results show that a thin crystalline silica layer is formed on the anodically etched rough surface of the PPS films. When this layer is removed, the photoluminescence intensity decreases sharply, whereas the micro-Raman resonance peak (near 517 cm−1) does not shift but its intensity increases significantly. The mechanisms for these observations are discussed in detail.
    Microelectronics Reliability 01/2001; 41:179-184. · 1.14 Impact Factor
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    ABSTRACT: Porous silicon (PS) offers many potential advantages for the realization of optoelectronic applications. However, the electrochemical anodizing method used to fabricate porous silicon has resulted in many undesirable sub-effects, such as impurities due to reactive residents, nonstabilized surface, nonuniform pore structure, and high film stress, leading to contamination of conventional VLSI processes. In this paper, we report a new dry etching method to produce the light-emitting PS. The formation mechanism of this film is proposed. Using the samples prepared with this new method, results demonstrate that the luminescence in this film does not have strong correlation with size of the nano-structures and we therefore suggest that the luminescence in this film is not due to the quantum confinement effects
    01/2001;
  • B.L. Yang, H Wong, P.G. Han, M.C. Poon
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    ABSTRACT: This work reports some electrical characteristics of ultra-shallow (~90 nm) n<sup>+</sup>p junctions fabricated using plasma immersion implantation of arsenic ions. Both forward and reverse current-voltage (IV) characteristics at operation temperatures ranging from 100 to 450 K were measured. Results show that the ideality factor varies from unity to two indicating both diffusion and GR processes are important in these devices. The ideality factor is found to fluctuate with the temperature, indicating that discrete trap centers exist in these samples. Annealing has a profound effect on the reverse diode characteristics. For fully activated sample, the IV relationship essentially follows a power law, i.e I∝V<sup>m</sup>. The power index m&ap;3 and almost remains unchanged at different temperatures
    Microelectronics, 2000. Proceedings. 2000 22nd International Conference on; 02/2000
  • H Wong, P.G. Han, M.C. Poon, Y. Gao
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    ABSTRACT: The surface properties of porous silicon (PS) play a vital role in its applications in optoelectronic devices and PS-based chemical/biological sensory devices. We have investigated the effects of reactive ion etching (RIE) treatment on the surface structures, optical properties and internal stresses of the PS films. Experimental results show that there is a thin layer of glassy, mirror-like material covered on the top of the PS films and the main composites of this layer are silicon oxides. When removing away this layer, the photoluminescence (PL) intensities decrease sharply, micro-Raman resonant peaks (near 516 cm<sup>-1</sup>) shift slightly and the intensities reduce significantly. The functions of the top layer and mechanisms of interaction with PS films will be discussed in this paper
    Electron Devices Meeting, 2000. Proceedings. 2000 IEEE Hong Kong; 02/2000
  • P. G. Han, H. Wong, M. C. Poon, N. Wang
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    ABSTRACT: Porous polycrystalline silicon (PPS) based conductivity sensors were fabricated and characterized in this work. The PPS sensors show excellent sensitivity for detecting ambient pressures, gas species as well as temperature. Results show that the current increases significantly as the pressure decreases and an over two orders of magnitude change has been detected when the pressure was reduced to 10<sup>-2</sup> atm. We also find that both ethanol and acetone vapors can significantly change the conduction in the sensors. In acetone vapor, the device even displays diode-like characteristics. Electrical conduction mechanisms of the sensors in vacuum and organic vapors are proposed. The fabrication process can be easily integrated with very large scale integrated technology. © 1999 American Vacuum Society.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 08/1999; · 1.43 Impact Factor
  • P.G Han, H Wong, M.C Poon
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    ABSTRACT: This paper reports the surface electronic structure of light-emitting porous polycrystalline silicon (PPS) using X-ray photoelectron spectroscopy (XPS). We find that the PPS films with strong photoluminescence (PL) effect can only be observed in thin film with trace amount of silicon nanoclusters and the luminescence can be enhanced remarkably with proper passivation of the PPS surface. Incomplete oxidation of silicon (Si3+ or Si2+) does not lead to visible PL. We further estimate that the average size of silicon nanoclusters is in the range of 20–30 Å in the sample having PL emission.
    Microelectronics Reliability 01/1999; 39(4):457-462. · 1.14 Impact Factor
  • H Wong, P.G. Han, M.C. Poon
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    ABSTRACT: Low-frequency (LF) noise measurements, at room temperature and above the Curie point, were conducted in barium titanate ceramic resistors. Experiments show that the LF noise behaviors are governed by grain boundary tunneling at room temperature and by trapping and detrapping of the grain boundary states at temperatures above the Curie point and their physical models are developed, These observations provide additional information on the current conduction and the distribution of grain boundary states in these materials
    Electron Devices Meeting, 1998. Proceedings., 1998 IEEE Hong Kong; 09/1998
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    ABSTRACT: An abnormal field dependence of resistivity is observed in BaTiO <sub>3</sub> positive temperature coefficient resistors (PTCRs) with a small averaged grain size. With this connection, a grain boundary tunneling model for the current conduction is proposed. This new model agrees with the both the measured electric field and temperature dependencies. It suggests that grain boundary tunneling of carrier is as important as the double Schottky barrier in the current conduction in small grain size BaTiO<sub>3</sub> PTCRs
    Electron Devices Meeting, 1998. Proceedings., 1998 IEEE Hong Kong; 09/1998
  • P.G. Han, H. Wong, M.C. Poon
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    ABSTRACT: A thin layer of p-type anodized porous polycrystalline silicon (PPS) are formed on n-type epitaxial crystal silicon wafer. The sensitivity of the resistors based on this PPS has been characterized and analyzed at different ambient pressures and temperature as well as gas species. Results show that the current-voltage characteristics are highly sensitive to the ambient pressure and organic gases. In addition, the effects of illumination and temperature are also studied.
    Electron Devices Meeting, 1998. Proceedings. 1998 IEEE Hong Kong; 01/1998
  • P.G. Han, H Wong, M.C. Poon
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    ABSTRACT: Surface electronic structure of light-emitting porous polycrystalline silicon (PPS) is studied using X-ray photoelectron spectroscopy (XPS). We find that the PPS films with strong photoluminescence effect can only be observed in thin films with trace amounts of silicon nanoclusters and the luminescence can be enhanced remarkably with proper passivation of the PPS surface
    Electron Devices Meeting, 1997. Proceedings., 1997 IEEE Hong Kong; 09/1997
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    ABSTRACT: Metal silicides have been widely used in microelectronic industries, especially as contact material to reduce the series resistance of source, drain and gate regions in MOSFETs. Among all silicides, cobalt-disilicide (CoSi<sub>2</sub>) and nickel-monosilicide (NiSi) have been demonstrated to be two of the most promising silicide materials for future ULSI, thin film transistor (TFT) and novel devices. They have the advantages of having the lowest resistivities (~14 μohm-cm), good thermal stability (up to 700-900°C), low formation temperature (~400-600 °C) and little or no resistivity degradation on narrow lines/gates. Moreover, for CoSi<sub>2</sub>, it can have low film stress (lattice mismatch with silicon (Si) is only 1.2%), less lateral gate-source/drain silicide overgrowth, good resistance to HF and plasma etching, and do not react with oxide below 900°C. For NiSi, it has the advantages of less Si consumption, no reaction with N<sub>2 </sub> and a simple single step annealing. This paper aims to provide a first study to explore and compare the thermal stability and process windows of NiSi and CoSi<sub>2</sub> in amorphous Si (a-Si) and single-crystalline Si (c-Si) substrates after 30 minutes long time annealing
    Electron Devices Meeting, 1997. Proceedings., 1997 IEEE Hong Kong; 09/1997
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    ABSTRACT: Several positive temperature coefficient resistors (PTCR's) are prepared using commercially available BaTiO<sub>3</sub> powders with different additives (Y, Mn, Nb, AST). We found that the different additives will result in different grain sizes, grain surface and porosity. However, the temperature-dependent resistivities of these samples do not have significant difference. A new model is proposed to explain this discrepancy and the three-segment characteristics in the PTCR
    Electron Devices Meeting, 1997. Proceedings., 1997 IEEE Hong Kong; 09/1997
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    ABSTRACT: In this work, we found that very low resistivity NiSi can be thermally stable and is independent of linewidth for deep submicron p-type poly-Si lines up to 700-750°C for 0.5 and 1 hr annealing, and for linewidths as narrow as 0.2-0.1 μm. It widens the thermal budget windows and process tolerance for NiSi and further suggests that NiSi is a very promising contact material candidate for future ULSI devices
    Electron Devices Meeting, 1997. Proceedings., 1997 IEEE Hong Kong; 09/1997
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    ABSTRACT: Luminescent porous poly‐Si thin films can be obtained by electrochemical etching of phosphorus‐doped poly‐Si films deposited by low‐pressure chemical‐vapor deposition. As‐deposited poly‐Si film has no photoluminescence but all porous poly‐Si films, large area or micron‐size patterns, show comparable orange‐red photoluminescences to those obtained from crystal Si. High‐resolution atomic force microscopy and scanning electron microscopy analyses show that all porous poly‐Si films have smooth surfaces and uniform thicknesses, and are composed of Si grains (∼150 nm) with nanopores (∼20 nm) formed around the surfaces. The pores increase with anodization time, and grow preferentially along the poly‐Si grain boundaries and the Si 〈100〉 crystal directions. The evolution of the microstructure is analogous to that of the etching of a coral ball layer due to sea water. © 1996 American Vacuum Society
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 04/1996; · 1.36 Impact Factor
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    ABSTRACT: Polycrystalline silicon (poly-Si) thin films (∼700nm) were deposited by LPCVD, doped with 950°C phosphorous diffusion, and rendered porous by anodization and stain etching. From x-ray photoelectron spectroscopy, poly-Si films have atomic concentration of C(ls):0(ls):Si(2p) = 6%:15%:79%. However, porous poly-Si (PPS) films with weak photoluminescence (PL) have C:O:Si of 20%:38%:42%. For PPS films with strong PL, C:O:Si is 11%:38%:51%. From micro-Raman, scattered spectra for 632nm laser source has peak at 735nm and full wave half maximum (FWHM) of 76nm, and is similar to the PL spectra excited by 400nm uv laser source. High resolution transmission electron microscopy (TEM) study shows that PPS film is of complex structure and composes of numerous Si nano-crystals (1∼10nm) surrounded by amorphous materials.
    MRS Proceedings. 12/1995; 452.
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    ABSTRACT: This paper will present new growth mechanisms, nanostructures and photoluminescence results on porous polycrystalline silicon films. The possible explanations and models will also be proposed and discussed
    Microelectronics and VLSI, 1995. TENCON '95., IEEE Region 10 International Conference on; 12/1995

Publication Stats

30 Citations
9.45 Total Impact Points

Institutions

  • 2001–2002
    • City University of Hong Kong
      • Department of Electronic Engineering
      Chiu-lung, Kowloon City, Hong Kong
  • 1995–2002
    • The Hong Kong University of Science and Technology
      • Department of Electronic and Computer Engineering
      Chiu-lung, Kowloon City, Hong Kong
  • 1997–2001
    • The University of Hong Kong
      • Department of Electrical and Electronic Engineering
      Hong Kong, Hong Kong
  • 2000
    • University of California, Berkeley
      • Department of Electrical Engineering and Computer Sciences
      Berkeley, MO, United States