L. P. You

Peking University, Peping, Beijing, China

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Publications (38)96.28 Total impact

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    ABSTRACT: A correlation between microstructures and high gate leakage current density of Schottky contacts on lattice-matched InxAl1−xN/GaN heterostructures has been investigated by means of current-voltage measurements, conductive atom force microscopy (C-AFM), and transmission electron microscopy (TEM) investigations. It is shown that the reverse-bias gate leakage current density of Ni/Au Schottky contacts on InxAl1−xN/GaN heterostructures is more than two orders of magnitude larger than that on AlxGa1−xN/GaN ones. C-AFM and TEM observations indicate that screw- and mixed-type threading dislocations (S/M-TDs) are efficient leakage current channels in InxAl1−xN barrier and In segregation is formed around S/M-TDs. It is believed that In segregation around S/M-TDs reduces local Schottky barrier height to form conductive channels and leads to high leakage current density of Schottky contacts on InxAl1−xN/GaN heterostructures.
    Full-text · Article · Dec 2010 · Applied Physics Letters
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    Y. Ye · L. Dai · T. Sun · L. P. You · R. Zhu · J. Y. Gao · R. M. Peng · D. P. Yu · G. G. Qin
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    ABSTRACT: High-quality straight and multiply kinked CdTe nanowires (NWs) were synthesized by the facile chemical vapor deposition method at 600 °C. The as-synthesized NWs were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence (PL) spectroscopy. The straight CdTe NWs have single crystalline zinc blende structure with growth direction along the 〈111〉 direction. Their PL spectra consist only sharp near band edge emission around 824.3 nm. The multiply kinked CdTe NWs contain one or more fixed ( ∼ 125.2°) angle joints; each arm of the kinked NWs is single crystalline with similar selected area electron diffraction pattern as that of the straight CdTe NWs. The two growth directions in the multiply kinked CdTe NWs are 〈200〉 and 〈111〉. Single straight and kinked CdTe NW photoresponse devices were fabricated and testified to have high photocurrent decay ratio, high responsivity, fast response time, and no decay tail under 633 nm He–Ne laser illumination. These straight and multiply kinked CdTe NWs may open up potential applications in the bottom-up integrated nanoelectronic and nanophotonic systems, such as photovoltaic and multiterminal nanodevices etc.
    Full-text · Article · Aug 2010 · Journal of Applied Physics
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    ABSTRACT: Light emitting diodes (LEDs) using InGaN/GaN quantum wells (QWs) with thin low temperature GaN (LT-GaN) layers bounding each InGaN layer are grown by metal-organic vapor phase epitaxy. The light output power of such LEDs increases by a factor of 2 at a drive current density of 35 A / cm <sup>2</sup> compared to that from reference LEDs without the LT-GaN. The blueshift in the emission wavelength is 5.2 nm when the current density increases from 3 to 50 A / cm <sup>2</sup> , which is much smaller than the shift 8.1 nm from reference LEDs. Moreover, the efficiency droop at high current injection is also reduced by 28%, and current density at which peak efficiency is observed increases from 1 to 2 A / cm <sup>2</sup> . High resolution transmission electron microscopy of the QWs bounded with LT-GaN shows higher quality and less strain compared to the reference samples. The better performance of LEDs incorporating the LT-GaN layers is attributed to suppressed polarization from piezoelectric fields.
    Full-text · Article · Jun 2010 · Journal of Applied Physics
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    ABSTRACT: A kind of inversion domains (IDs) which originated from the tips of threading dislocations were observed in the Al0.65Ga0.35N layer by transmission electron microscopy (TEM). The IDs showed columnar structures with diameters of 10–20 nm. We find that the dislocations evolved into V-shape boundaries then form IDs. By high resolution TEM analysis, the atomic structure at the boundary was proved to be the IDB∗ structure, in which each atom remains fourfold coordinated without the formation of Ga–Ga or N–N bonds.
    No preview · Article · Sep 2009 · Applied Physics Letters
  • C Liu · L Dai · L P You · W J Xu · G G Qin
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    ABSTRACT: Single-crystalline n-type InP nanowires (NWs) with different electron concentrations were synthesized on Si substrates via the vapor phase transport method. The electrical properties of the InP nanowires were investigated by fabricating and measuring single NW field-effect transistors (FETs). Single InP NW/p(+)-Si heterojunctions were fabricated, and electroluminescence (EL) spectra from them were studied. It was found that both the photoluminescence (PL) spectra of the InP NWs and the EL spectra of the heterojunctions blueshift from 920 to 775 nm when the electron concentrations of the InP NWs increase from 2 × 10(17) to 1.4 × 10(19) cm(-3). The blueshifts can be attributed to the Burstein-Moss effect rather than the quantum confinement effect in the InP NWs. The large blueshifts observed in this study indicate a potential application of InP NWs in nano-multicolour displays.
    No preview · Article · Nov 2008 · Nanotechnology
  • C. Liu · L. Dai · L. P. You · W. J. Xu · R. M. Ma · W. Q. Yang · Y. F. Zhang · G. G. Qin
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    ABSTRACT: Single-crystalline Zn3P2 nanowires (NWs) have been synthesized on silicon (Si) substrates via a vapor phase transport method. Zn (99.99%) powder and InP (99.99%) fragments were used as the sources, and 10 nm thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared Zn3P2 NWs have diameters of 100–200 nm and lengths of more than 10 μm. Single NW metal–insulator–semiconductor field-effect transistors (MISFETs) based on Zn3P2 NWs were fabricated. Electrical transport measurements show that the as-grown Zn3P2 NWs are of p-type. The hole concentrations and mobilities of the p-type Zn3P2 NWs are about 5.6 × 1016 cm−3 and 42.5 cm2 V−1 s−1, respectively. The on–off ratio of the MISFET is about 4 × 104, and its threshold voltage and transconductance are 2.5 V and 35 nS, respectively. These parameters indicate that the p-type Zn3P2 NWs are of high quality, and may have potential applications in nanoscale electronic and optoelectronic devices.
    No preview · Article · Aug 2008 · Journal of Materials Chemistry
  • W. Q. Yang · L. Dai · L. P. You · G. G. Qin
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    ABSTRACT: Unintentionally doped and Cu and Mn doped ZnS nanobelts were synthesized via the vapor phase transport method. The nanobelts have the single crystalline wurtzite structure. By modifying the mass ratio of source to dopant, the photoluminescence (PL) spectra from the Cu and Mn doped ZnS nanobelts can be tuned to center around 450 nm (blue) and 580 (orange), respectively. The PL spectra from the unintentionally doped ones synthesized in highly purified N2 and N2/H2 gases center around 520 nm (green) and 660 nm (red), respectively. As far as we know, the blue colored PL of Cu doped ZnS nanobelts and the red colored PL of ZnS nanobelts are reported for the first time. In this way, the PL color from ZnS nanobelts can be tuned from blue to red. The ZnS nanobelts have potential application in the nano-multicolor displays.
    No preview · Article · Jun 2008 · Physics Letters A
  • K Sun · W J Xu · B Zhang · L P You · G Z Ran · G G Qin
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    ABSTRACT: The roles of amorphous Si nanoparticles in light-emitting diodes (LEDs) based on Er-doped Si(1+x)O(2) films (x representing the degree of Si content, and varying widely from 0 to 4.50) have been investigated. In the aspect of the LEDs' electrical performance, it was found that the incorporation of Si nanoparticles facilitates the electrical conductivity of the films by improving the carrier mobility. With x increasing from 0 to 4.50, the mobility increases monotonically up to 5 times. The efficiency of Er(3+) electroluminescence (EL) at 1.54 µm can be enhanced by as much as 160 times when the degree of Si content x is 2.00, coincident with the value at which the rate of mobility increasing versus x slows down. The fact that the maximum of EL efficiency and the slowing down of the rate of increase of mobility occur at the same x value can be explained by coalescence of Si nanoparticles starting at x = 2.
    No preview · Article · Mar 2008 · Nanotechnology
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    ABSTRACT: In this paper, an electrical measurement method to identify shallow dopants in lowly doped semiconductor nanowires was suggested. Room temperature electrical measurement indicates that electron concentrations of the n-GaN nanowires are about 5.4×1017 cm-3. Temperature-dependent measurement of conductivities of single nanowires in low temperature region gives activation energy of 13.3 meV, which is consistent with the reported activation energy of 14 meV for Si donor in n-GaN films with donor concentration of 7.4×1017 cm-3. Our results confirm that the shallow donors in the as-synthesized GaN nanowires are silicon. We consider such a method may be applicable to other semiconductor nanowires.
    No preview · Article · Oct 2007 · Applied Physics Letters
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    ABSTRACT: The structural influences of the laser lift-off (LLO) techniques on the created (0001) GaN surface region are characterized by cross-sectional high-resolution transmission electron microscopy and fitted using the model of stress waves caused by a longitudinal impact at the end of a cylindrical bar extending to infinity. The authors study reveals that, in addition to the superficial damage caused by laser absorption, the stress saltation in GaN crystal where the shock waves come into being induces deformation of the lattices and generates a cluster of half loops above the LLO interface. After that, the lattice deformation will be induced every time the partial dissipation of the steady-state shock waves takes place until the shock wave is dissipated to elastic mode.
    Full-text · Article · Sep 2007 · Applied Physics Letters
  • Y.F. Zhang · L.P. You · X.D. Shan · X.L. Wei · H.B. Huo · W.J. Xu · L. Dai
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    ABSTRACT: Single-crystalline Si−CdSe biaxial p−n heterostructure nanowires (NWs) have been grown via chemical vapor deposition method and characterized. The Si and CdSe subnanowires have diameters of about 30 and 60 nm, respectively, and grow along the [2̄11̄] and [0001] directions, respectively. Room-temperature photoluminescence (PL), Raman-scattering, and electrical transport measurements were made on single Si−CdSe biaxial heterostructure NWs. Strong CdSe band-edge emission peaked around 710 nm together with a broad emission centered at 600 nm is observed in the PL spectra. Intense sharp longitudinal optical phonon modes from both CdSe and Si are observed in Raman-scattering spectra. The resistivities, carrier concentrations, and carrier mobilities of single CdSe NW and Si subnanowire are estimated. A good rectification characteristic is observed in the I−V curve of Si−CdSe biaxial NW, which confirms that the Si−CdSe biaxial NW is a p−n heterostructure.
    No preview · Article · Sep 2007 · The Journal of Physical Chemistry C
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    H Z Zhang · R M Wang · L P You · J Yu · H Chen · D P Yu · Y Chen
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    ABSTRACT: Boron carbide nanowires with uniform carbon nitride coating layers were synthesized on a silicon substrate using a simple thermal process. The structure and morphology of the as-synthesized nanowires were characterized using x-ray diffraction, scanning and transmission electron microscopy and electron energy loss spectroscopy. A correlation between the surface smoothness of the nanowire sidewalls and their lateral sizes has been observed and it is a consequence of the anisotropic formation of the coating layers. A growth mechanism is also proposed for these growth phenomena.
    Full-text · Article · Jan 2007 · New Journal of Physics
  • W Q Yang · L Dai · L P You · B R Zhang · B Shen · G G Qin
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    ABSTRACT: Well-aligned ZnO nanowires have been synthesized vertically on In0.2Ga0.8N, GaN, and Al0.25Ga0.75N substrates, using a catalyst-free carbon thermal-reduction vapor phase deposition method for the first time. The as-synthesized nanowires are single crystalline wurtzite structure, and have a growth direction of [0001]. Each nanowire has a smooth surface, and uniform diameter along the growth direction. The average diameter and length of these nanowires are 120-150 nm, and 3-10 )m, respectively. We suggest that the growth mechanism follow a self-catalyzing growth model. Excitonic emission peaked around 385 nm dominates the room-temperature photoluminescence spectra of these nanowires. The room-temperature photoluminescence and Raman scattering spectra show that these nanowires have good optical quality with very less structural defects.
    No preview · Article · Jan 2007 · Journal of Nanoscience and Nanotechnology
  • W. Q. Yang · L. Dai · L. P. You · B. R. Zhang · B. Shen · G. G. Qin
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    ABSTRACT: Well-aligned ZnO nanowires have been synthesized vertically on In0.2Ga0.8N, GaN, and Al0.25Ga0.75N substrates, using a catalyst-free carbon thermal-reduction vapor phase deposition method for the first time. The as-synthesized nanowires are single crystalline wurtzite structure, and have a growth direction of [0001]. Each nanowire has a smooth surface, and uniform diameter along the growth direction. The average diameter and length of these nanowires are 120–150 nm, and 3–10 m, respectively. We suggest that the growth mechanism follow a self-catalyzing growth model. Excitonic emission peaked around 385 nm dominates the room-temperature photoluminescence spectra of these nanowires. The room-temperature photoluminescence and Raman scattering spectra show that these nanowires have good optical quality with very less structural defects.
    No preview · Article · Dec 2006 · Journal of Nanoscience and Nanotechnology
  • H B Huo · L Dai · C Liu · L P You · W Q Yang · R M Ma · G Z Ran · G G Qin
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    ABSTRACT: Single crystalline zincblende p-ZnTe nanowires (NWs) were synthesized via the vapour phase transport method. Based on either as-grown or Cu doped ZnTe NWs, single NW field effect transistors were fabricated and they were used to study the electrical properties of ZnTe NWs. Electrical transport measurements show that the as-grown ZnTe NWs are of p-type and very high resistivity. After 30 min immersion in Cu(NO3)2 solution, their conductivity can be increased by about three orders of magnitude. The hole concentrations of the p-type ZnTe nanowires could be controlled in a range from 7.0 × 1017 to 3.5 × 1018 cm−3 by changing the immersion duration. The doped p-type ZnTe NWs may have potential applications in nanoscale electronic and optoelectronic devices.
    No preview · Article · Nov 2006 · Nanotechnology
  • H B Huo · L Dai · DY Xia · G Z Ran · L P You · B R Zhang · G G Qin
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    ABSTRACT: Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.
    No preview · Article · May 2006 · Journal of Nanoscience and Nanotechnology
  • Y.H. Zhang · J. Liu · T. Liu · L.P. You · X.G. Li
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    ABSTRACT: Two types of ZnO single-sided nanocombs, namely the straight comb and the crescent comb, have been synthesized by simple evaporation of Zn powder in diluted O2 flow at 440 °C. Both combs have a common teeth growth direction of [0 0 0 1]. The backbone of the straight comb is a oriented nanobelt, with combteeth distributed on its broader surface. The backbone of the crescent comb is a oriented nanobelt, with combteeth distributed on its narrower surface, and it is bent into an arc by stress. The crescent comb is interesting as it is not only a hierarchical assembly of one-dimensional nanostructures, but also folded into a secondary structure as well. The structures of our nanocombs are controlled by supersaturation. Taking advantage of our low-temperature synthesis, we studied the growth process by freezing the growth stages. A modified VS growth mechanism was proposed.
    No preview · Article · Dec 2005 · Journal of Crystal Growth
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    L Dai · S F Liu · L P You · J C Zhang · G G Qin
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    ABSTRACT: GaN nanowires have been grown with and without In as an additional source. The effects of In surfactant on the crystal quality and photoluminescence property of GaN nanowires are reported for the first time. X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence measurements are employed to analyse the products. The results show that introducing a certain amount of In surfactant during the growth process can improve the crystal quality of the GaN nanowires, and enhance the photoluminescence of them. In addition, the as-prepared GaN nanowires have the advantage of being easy to be separated, which will benefit the subsequent nanodevice fabrication.
    Preview · Article · Oct 2005 · Journal of Physics Condensed Matter
  • S.-F. Liu · G.-G. Qin · L.-P. You · J.-C. Zhang · Z.-X. Fu · L. Dai
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    ABSTRACT: A two-hot-boat chemical vapor deposition system was modified from a thermal evaporation equipment. This system has the advantage of high vacuum, rapid heating rate and temperature separately controlled boats for the source and samples. These are in favor of synthesizing compound semiconducting nano-materials. By the system, we have synthesized high-quality wurtzite single crystal GaN nanowires and nanotip triangle pyramids via an in-situ doping indium surfactant technique on Si and 3C-SiC epilayer/Si substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence measurements. The GaN nanotip triangle pyramids, synthesized with this novel method, have potential application in electronic/photonic devices for field-emission and laser.
    No preview · Article · Sep 2005 · Acta Physica Sinica -Chinese Edition-
  • L Dai · S F Liu · Z X Fu · L P You · J J Zhu · B X Lin · J C Zhang · G G Qin
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    ABSTRACT: GaN nanotip triangle pyramids were synthesized on 3C-SiC epilayer via an isoelectronic In-doping technique. The synthesis was carried out in a specially designed two-hot-boat chemical vapor deposition system. In (99.999%) and molten Ga (99.99%) with a mass ratio of about 1:4 were used as the source, and pieces of Si (111) wafer covered with 400-500 nm 3C-SiC epilayer were used as the substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, and photoluminescence measurements. Our results show that the as-synthesized GaN pyramids are perfect single crystal with wurtzite structure, which may have potential applications in electronic/photonic devices.
    No preview · Article · Apr 2005 · The Journal of Chemical Physics

Publication Stats

681 Citations
96.28 Total Impact Points

Institutions

  • 1997-2010
    • Peking University
      • • Electron Microscopy Laboratory
      • • Department of Physics
      Peping, Beijing, China
  • 2003-2005
    • University of Michigan
      • Department of Nuclear Engineering and Radiological Sciences
      Ann Arbor, MI, United States
    • Zhongshan University
      中山, Guangdong, China