S. J. Pearton

University of Florida, Gainesville, Florida, United States

Are you S. J. Pearton?

Claim your profile

Publications (981)1504.52 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The valence band discontinuity (ΔEV) of Y2O3/InGaZnO4 (IGZO) heterojunctions was measured by a core-level photoemission method. The Y2O3 exhibited a band gap of ∼6.27 eV from absorption measurements. A value of ΔEV = 0.44±0.21 eV was obtained by using the Ga 2p3/2, Zn 2p3/2 and In 3d5/2 energy levels as references. Given the experimental bandgap of 3.2 eV for the IGZO, this would indicate a conduction band offset ΔEC of ∼2.63 eV in the Y2O3/IGZO heterostructures and a nested interface band alignment.
    Journal of Nanoscience and Nanotechnology 11/2014; 14(11). · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate GaN-based thin light-emitting diodes (LEDs) on flexible polymer and paper substrates covered with chemical vapor deposited graphene as a transparent-conductive layer. Thin LEDs were fabricated by lifting the sapphire substrate off by Excimer laser heating, followed by transfer of the LEDs to the flexible substrates. These substrates were coated with tri-layer graphene by a wet transfer method. Optical and electrical properties of thin laser lift-offed LEDs on the flexible substrates were characterized under both relaxed and strained conditions. The graphene on paper substrates remained conducting when the graphene/paper structure was folded. The high transmittance, low sheet resistance and high failure strain of the graphene make it an ideal candidate as the transparent and conductive layer in flexible optoelectronics.
    Optics express. 05/2014; 22(S3):A812-A817.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The energy discontinuity in the valence band (deltaE(v)) of Y2O3-stabilized ZrO2 (YSZ)/InGaZnO4 (IGZO) heterostructures was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The YSZ exhibited a bandgap of 4.4 eV from absorption measurements. A value of deltaE(v) = 0.57 +/- 0.12 eV was obtained by using Ga 2P3/2, Zn 2p3/2 and In 3d5/2 energy levels as references. This implies a conduction band offset (deltaE(c)) of 0.63 eV in YSZ/InGaZnO4 heterostructures and a nested interface band alignment.
    Journal of Nanoscience and Nanotechnology 05/2014; 14(5):3925-7. · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate GaN-based thin light-emitting diodes (LEDs) on flexible polymer and paper substrates covered with chemical vapor deposited graphene as a transparent-conductive layer. Thin LEDs were fabricated by lifting the sapphire substrate off by Excimer laser heating, followed by transfer of the LEDs to the flexible substrates. These substrates were coated with tri-layer graphene by a wet transfer method. Optical and electrical properties of thin laser lift-offed LEDs on the flexible substrates were characterized under both relaxed and strained conditions. The graphene on paper substrates remained conducting when the graphene/paper structure was folded. The high transmittance, low sheet resistance and high failure strain of the graphene make it an ideal candidate as the transparent and conductive layer in flexible optoelectronics.
    Optics Express 04/2014; 22(S3). · 3.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Deep hole traps were studied in bulk free-standing GaN crystals and in thinner (10–20 μm) GaN films prepared by hydride vapor phase epitaxy (HVPE) on sapphire. Six hole traps in different combinations were detected in these crystals, H1 (activation energy 0.92–0.94 eV), H2 (0.55 eV), H3 (0.65–0.7 eV), H4 (0.85–0.9 eV), H5 (1.1–1.2 eV), and H6 (0.95–1.05 eV). The dominant traps in all samples were the H5 and H6 traps that were attributed, respectively, to gallium vacancy complexes with oxygen (VGa-O) and substitutional carbon related centers. We associate the H5 hole traps with the red luminescence bands, the H4 hole traps with the green luminescence bands, and the H6 hole traps with the yellow luminescence bands often observed in HVPE GaN. These attributions are based on the low energy thresholds of the deep traps optical excitation spectra and the depth of the respective trap levels.
    Journal of Applied Physics 01/2014; 115(22):223702-223702-5. · 2.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Proton irradiation from the backside of the samples were employed to enhance off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for subsequent backside proton irradiation. By taking the advantage of the steep drop at the end of proton energy loss profile, the defects created by the proton irradiation from the backside of the sample could be precisely placed at specific locations inside the AlGaN/GaN HEMT structure. There were no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for the irradiated AlGaN/GaN HEMTs with the proton energy of 225 or 275 keV, for which the defects created by the proton irradiations were intentionally placed in the GaN buffer. HEMTs with defects placed in the two dimensional electron gas (2DEG) channel region and AlGaN barrier using 330 or 340 keV protons not only showed degradation of both drain current and extrinsic transconductance but also exhibited improvement of the off-state drain breakdown voltage. The Florida Object Oriented Device and Process Simulator Technology Computer Aided Design finite-element simulations were performed to confirm the hypothesis of a virtual gate formed around the 2DEG region to reduce the peak electric field around the gate edges and increase the off-state drain breakdown voltage.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2014; 32(2):021203-021203-6. · 1.36 Impact Factor
  • Source
    S.J Pearton, F. Ren
    [Show abstract] [Hide abstract]
    ABSTRACT: ZnO and related semiconductors are alternatives to GaN-based compounds for fabrication of UV/blue light emitting diodes (LEDs). Progress in development of ZnO LEDs has been disappointing due to the difficulty of achieving robust p-type doping and the low crystal quality of heterojunctions and quantum wells. We critically review reports of p-type doping using group V impurities and summarize recent progress and prospects for further advancement of ZnO-based light emitters.
    Current Opinion in Chemical Engineering. 01/2014; 3:51–55.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of proton irradiation on the off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates was studied by irradiating protons from the backside of the samples through via holes fabricated directly under the active area of the HEMTs. There was no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for HEMTs irradiated with 275 keV protons, for which the defects created by the proton irradiation were intentionally placed in the GaN buffer. HEMTs with defects positioned in the 2 dimensional electron gas channel region and AlGaN barrier using 330 keV protons not only showed degradation of both drain current and extrinsic transconductance but also exhibited an improvement of the off-state drain breakdown voltage. Finite-element simulations showed the enhancement of the latter were due to a reduction in electric field strength at the gate edges by introduction of charged defects.
    Applied Physics Letters 01/2014; 104(8):082106-082106-3. · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The authors report an investigation of the effect of different doses of 5 MeV proton irradiation on circular-shaped AlGaN/GaN high electron mobility transistors. The degradation of saturation drain current (IDSS) was minimal up to an irradiation dose of 2 × 1013 cm−2. By comparison, a dose of 2 × 1014 cm−2 dose produced a 12.5% reduction of IDSS and 9.2% increase of sheet resistance. In addition, the threshold voltage showed larger positive shifts for 2×1014 cm−2 dose compared to 2×1013 cm−2, and both of these doses produced showed larger shifts for smaller gate to drain distances. Increases of 39.8% and 47.1%, respectively, in the breakdown voltage for 6 and 10 μm drain to gate distances (LGD) was observed and was attributed to the creation of a virtual gate at the AlGaN/GaN interface due to the irradiation, which reduced the peak electric field at the drain side of the gate edge.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2014; 32(1):012201-012201-7. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of proton irradiation dose on the dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with source field plates were studied. The HEMTs were irradiated with various protons doses ranging from 5 × 1012 to 5 × 1015 cm−2 at a fixed energy of 5 MeV. HEMTs irradiated with proton dose below 5 × 1013 cm−2 showed less than 2% degradation of either saturation drain current (IDSS) or transconductance (gm). Significant changes of these parameters were observed for the devices irradiated with doses above 5 × 1013 cm−2. HEMTs irradiated with the highest proton dose of 5 × 1015 cm−2 showed a reduction of IDSS and gm of 86% and 64.7%, and a positive Vth shift of 0.84 V, respectively. Despite the significant IDSS and gm reductions, the off-state drain breakdown voltage (VBR) was improved more than five times at this particular irradiation condition. The significant improvement of off-state drain breakdown voltage was attributed to the formation of a virtual gate at drain side of gate edge, which was the result of the generation of defect centers at AlGaN/GaN interface.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2014; 32(2):022202-022202-6. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The changes in direct current performance of circular-shaped AlGaN/GaN high electron mobility transistors (HEMTs) after 60Co γ-irradiation doses of 50, 300, 450, or 700 Gy were measured. The main effects on the HEMTs after irradiation were increases of both drain current and electron mobility. Compton electrons induced from the absorption of the γ-rays appear to generate donor type defects. Drain current dispersions of ∼5% were observed during gate lag measurements due to the formation of a virtual gate between the gate and drain resulting from the defects generated during γ-irradiation.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2014; 32(3):031203-031203-5. · 1.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate AuCl<sub>3</sub>-doped graphene transparent conductive electrodes integrated in GaN-based ultraviolet (UV) light-emitting diodes (LEDs) with an emission peak of 363 nm. AuCl<sub>3</sub> doping was accomplished by dipping the graphene electrodes in 5, 10 and 20 mM concentrations of AuCl<sub>3</sub> solutions. The effects of AuCl<sub>3</sub> doping on graphene electrodes were investigated by current-voltage characteristics, sheet resistance, scanning electron microscope, optical transmittance, micro-Raman scattering and electroluminescence images. The optical transmittance was decreased with increasing the AuCl<sub>3</sub> concentrations. However, the forward currents of UV LEDs with p-doped (5, 10 and 20 mM of AuCl<sub>3</sub> solutions) graphene transparent conductive electrodes at a forward bias of 8 V were increased by ~48, 63 and 73%, respectively, which can be attributed to the reduction of sheet resistance and the increase of work function of the graphene. The performance of UV LEDs was drastically improved by AuCl<sub>3</sub> doping of graphene transparent conductive electrodes.
    Optics Express 11/2013; 21(23):29025-30. · 3.55 Impact Factor
  • Thin Solid Films 11/2013; · 1.87 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sb-based semiconductors incorporating heterostructures of InP, InAs, AlSb, InSb, GaSb, InGaAs, InGaSb, GaAsSb and InGaAsSb can be used for high speed, low power applications such as wide-bandwidth telecommunications for aircraft, satellites, wireless communication, and global positioning systems, as well as thermophotovoltaic cells, THz medical imaging and remote sensing, IR sensors for space exploration, high resolution biomedical spectroscopy and military systems, including security scanners. Sb-based electronic devices such as heterojunction bipolar transistors (HBTs) offer high speed, low power consumption and good breakdown voltages. High electron mobility InAs/AlSb or InSb/AlSb and high hole mobility InGaSb/AlSb quantum well heterostructure field effect transistors (HFETs) have also been widely pursued for THz amplifiers and high speed complementary logic circuits.
    J. Mater. Chem. C. 06/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on a simple and reproducible method for fabricating InGaN/GaN multi-quantum-well (MQW) nanorod light-emitting diodes (LEDs), prepared by combining a SiO<sub>2</sub> nanosphere lithography and dry-etch process. Focused-ion-beam (FIB)-deposited Pt was contacted to both ends of the nanorod LEDs, producing bright electroluminescence from the LEDs under forward bias conditions. The turn-on voltage in these nanorod LEDs was higher (13 V) than in companion thin film devices (3 V) and this can be attributed to the high contact resistance between the FIB-deposited Pt and nanorod LEDs and the damage induced by inductively-coupled plasma and Ga + -ions. Our method to obtain uniform MQW nanorod LEDs shows promise for improving the reproducibility of nano-optoelectronics.
    Optics Express 05/2013; 21(10):12908-13. · 3.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the effect of proton irradiation on reliability of InAlN/GaN high electron mobility transistors (HEMTs). Devices were subjected to 5-15 MeV proton irradiations with a fixed dose of 5 × 1015 cm-2, or to a different doses of 2 × 1011, 5 × 1013 or 2 × 1015 cm-2 of protons at a fixed energy of 5 MeV. During off-state electrical stressing, the typical critical voltage for un-irradiated devices was 45 to 55 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 100 V, which was instrument-limited. After electrical stressing, no degradation was observed for the drain or gate current-voltage characteristics of the proton-irradiated HEMTs. However, the drain current decreased ~12%, and the reverse bias gate leakage current increased more than two orders of magnitude for un-irradiated HEMTs as a result of electrical stressing.
    Proc SPIE 03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The hydrogen detection response time of Pt-gated diode sensors fabricated on AlGaN/GaN heterostructure as a function of the hydrogen concentration was investigated. A new method to extract the response time, taking the derivative of diode current, was proposed and shown to reduce the response time of detecting 1% hydrogen by about 60% as compared to the response time defined as the diode current reaching 90% of its total changes, t90. Hydrogen-sensing experiments were conducted at different temperatures, and an Arrhenius plot of the data determined an activation energy of 17.7 kJ/mole for the sensing process.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(3):2202-. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: InGaN/GaN vertical light emitting diodes (LEDs) with argon (Ar) and oxygen (O2) plasma-treated nonalloyed Al/Ti electrodes were fabricated on sapphire substrates. At the operating current of 350 mA, the forward voltage (VF) for O2 plasma-treated Al/Ti-based devices with dimensions 1360 × 1360 μm2 was improved, whose value was comparable or lower to that of nonalloyed Cr/Au-based devices. The Al/Ti electrodes resulted in improvement in optical output power of LEDs due to their high reflectivity (typically 10%–15% higher based on our data) compared to LEDs with conventional Cr/Au-based electrodes. The x-ray photoelectron spectroscopy showed the increase in Ga-O peak intensity during O2 plasma treatment. These results demonstrate that O2 plasma-treated Al/Ti electrodes reduced the contact resistance by forming a thin conductive GaOxN1-x layer at n-GaN surface.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(1):0602-. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Deep trap spectra in AlGaN/GaN high electron mobility transistor structures grown on Si by metalorganic chemical vapor deposition show four major electron traps (Ec—0.15, 0.29, 0.40 and 0.76 eV) in the AlGaN barrier/interface region and three (Ec—0.18, 0.27 and 0.45 eV) in the undoped GaN buffer region. The presence of a high density of deep acceptor traps was observed in the AlGaN barrier region, as determined by hysteresis in low temperature capacitance-voltage (C-V) characteristics. The spectral dependence of persistent photocapacitance shifts showed two optical thresholds of 1.5 V and 3.1 eV, with the second being specific to structures grown on Si substrates. Comparison of results obtained on transistors and on large-area Schottky diodes prepared on heterostructures from which transistors are fabricated show that measurements on test large-area diodes are representative of the main characteristics important for transistor performance.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(1):1211-. · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 μm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were ∼100 V, however, this degraded to 50–60 V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600–700 V), while a much smaller Viso of ∼200 V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(1):1805-. · 1.36 Impact Factor

Publication Stats

8k Citations
1,504.52 Total Impact Points

Institutions

  • 1994–2014
    • University of Florida
      • • Department of Materials Science and Engineering
      • • Department of Chemical Engineering
      • • Department of Physics
      Gainesville, Florida, United States
  • 2012
    • Korea University
      • Department of Chemical and Biological Engineering
      Seoul, Seoul, South Korea
  • 2007–2012
    • Kyungpook National University
      • School of Materials Science and Engineering
      Daikyū, Daegu, South Korea
  • 2010
    • Arizona State University
      • Department of Physics
      Mesa, AZ, United States
  • 2009
    • Yale University
      • Department of Electrical Engineering
      New Haven, CT, United States
  • 2002–2009
    • Inje University
      • School of Nano Engineering
      South Korea
  • 2008
    • National Central University
      • Department of Optics and Photonics
      Taoyuan City, Taiwan, Taiwan
  • 2002–2004
    • Wright-Patterson Air Force Base
      Dayton, Ohio, United States
  • 2003
    • Samsung Advanced Institute of Technology
      Usan-ri, Gyeonggi Province, South Korea
    • EMCORE Corporation
      Albuquerque, New Mexico, United States
  • 2001
    • Chonbuk National University
      • Semiconductor Physics Research Center
      Seoul, Seoul, South Korea
  • 1996–2000
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States
  • 1998
    • Australian National University
      • Department of Electronic Materials Engineering (EME)
      Canberra, Australian Capital Territory, Australia
  • 1993–1998
    • University of Southern California
      • Department of Electrical Engineering
      Los Angeles, CA, United States
    • Martin Marietta Laboratories
      Baltimore, Maryland, United States
  • 1992–1998
    • Lehigh University
      • Department of Physics
      Albuquerque, NM, United States
    • Carnegie Mellon University
      • Department of Electrical and Computer Engineering
      Pittsburgh, Pennsylvania, United States
  • 1989–1995
    • AT&T Labs
      Austin, Texas, United States
    • Spire Corporation
      Bedford, Massachusetts, United States
  • 1990
    • University of California, Los Angeles
      • Department of Materials Science and Engineering
      Los Angeles, CA, United States