S. J. Pearton

University of Florida, Gainesville, Florida, United States

Are you S. J. Pearton?

Claim your profile

Publications (817)1078.42 Total impact

  • [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
  • 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: AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon expose to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition (CVD), with perfect crystal quality will attach CO molecule and release electrons, which will lead to a change of surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezoinduced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200ppm in the open cavity with continuous gas flow using a 50x50mum2 gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor.
    Applied Physics Letters 08/2013; 103(8). · 3.79 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: A combination of TRIM and FLOODS models the effect of radiation damage on AlGaN/GaN HEMTs. While excellent fits are obtained for threshold voltage shift, the models do not fully explain the increased reliability observed experimentally. In short, the addition of negatively-charged traps in the GaN buffer layer does not significantly change the electric field at the gate edges at radiation fluence levels seen in this study. We propose that negative trapped charge at the nitride/AlGaN interface actually produces the virtual-gate effect that results in decreasing the magnitude of the electric field at the gate edges and thus the increase in critical voltage. Simulation results including nitride interface charge show significant changes in electric field profiles while the I-V device characteristics do not change.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4103-4108. · 1.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: AlGaN/GaN high electron mobility transistors were electrically stressed using off-state high reverse gate biases. In devices demonstrating the largest, most rapid decrease in normalized maximum drain current, defects were found at the gate/AlGaN epilayer interface and characterized using high-angle annular dark-field scanning transmission electron microscopy. These defects appear to be a reaction between the Ni layer of the Ni/Au gate metal stack and the AlGaN epilayer. Additionally, simulations of the electric field lines from the defective devices match the defect morphology. These results provide important insight toward understanding failure mechanisms and improving reliability of Ni-gate AlGaN/GaN high electron mobility transistors.
    Applied Physics Letters 01/2013; 103(2):023503-023503. · 3.79 Impact Factor
  • S.C. Hung, W.Y. Woon, S.M. Lan, F. Ren, S.J. Pearton
    [Show abstract] [Hide abstract]
    ABSTRACT: AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon exposure to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition, with perfect crystal quality will attach CO molecules and release electrons, which will lead to a change of surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezo-induced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200 ppm in the open cavity with continuous gas flow using a 50 × 50 μm2 gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor, respectively.
    Applied Physics Letters 01/2013; 103(8):083506-083506-4. · 3.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The emitter size effect of a series InGaAsSb base series of InP/InGaAsSb/InGaAs heterojunction bipolar transistors (HBTs) with different emitter sizes is investigated. Compared to the InGaAs base HBTs, these devices exhibit much lower base surface recombination current. This is attributed to the surface Fermi level pinning near the valence band of the antimonide base. The effect of Sb composition and doping concentration of the base on the surface recombination current is well explained by the postulate.
    Applied Physics Letters 08/2012; 101(7). · 3.79 Impact Factor
  • Young-Woo Heo, S J Pearton, D P Norton
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the size-dependent electrical conductivities of indium zinc oxide stripes with different widths from 50 nm to 4 microm and with the same thickness of 50 nm deposited by RF magnetron sputtering. The size of the indium zinc oxide stripes was controlled by e-beam lithography. The distance of the two Ti/Au Ohmic electrodes along the indium zinc oxide stripes was kept constant at 25 microm. The electrical conductivity decreased as the size of the indium zinc oxide stripes decreased below a critical width (80 nm). The activation energy, derived from the electric conductivity versus temperature measurement, was dependent on the dimensions of indium zinc oxide stripes. These results can be understood as stemming from surface charge trapping from the absorption of oxygen and/or water vapor, which leads to an increase in the energy difference between the conduction energy band and the Fermi energy.
    Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3264-7. · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Photoluminescence (PL) and optically detected magnetic resonance (ODMR) techniques are utilized to examine the effects of P implantation and post-implantation annealing on defect formation in ZnO single crystals. From ODMR, the main defects created by ion implantation include oxygen and zinc vacancies as a well as a deep donor labeled as PD. The formation of the PD defect is likely promoted by the presence of P as it could only be detected in the P-containing ZnO. The VO and PD centers are found to exhibit low thermal stability and can be annealed out at 800 °C. On the other hand, a new set of defects, such as Z, T, and D* centers, is detected after annealing. Based on measured spectral dependences of the ODMR signals, the VO, VZn, and PD centers are shown to participate in spin-dependent recombination processes related to red emissions, whereas the Z, T, and D* centers are involved in radiative recombination over a wide spectral range of 1.55–2.5 eV. From the PL measurements, combined effects of implantation and annealing also lead to appearance of a new PL band peaking at ∼3.156 eV, likely due to donor-acceptor-pair recombination. The formation of the involved deep acceptor is concluded to be facilitated by the presence of P.
    Journal of Applied Physics 02/2012; 111(4). · 2.21 Impact Factor
  • S. J. Pearton, Fan Ren
    [Show abstract] [Hide abstract]
    ABSTRACT: Semiconductor-based sensors are widely used for applications in detection of particular gases and liquids, fire detection, liquid quality monitoring, biosensing and medical sensing. As an example, our group has installed hydrogen sensors at a car dealership in Orlando, FL, USA, that houses a fleet of hydrogen-fuelled buses. These sensors are platinum (Pt)-coated aluminum gallium nitride (AlGaN) or gallium nitride (GaN) differential diodes whose output can be remotely monitored via an Internet connection and which provide an alarm both locally and to phones of relevant personnel. A screen-shot of the output of the six detector array is shown in Fig. 1.
    IEEE Instrumentation and Measurement Magazine 01/2012; 15:16-21. · 0.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of proton irradiation energy on dc and rf characteristics of InAlN/GaN high electron mobility transistors (HEMTs) were investigated. A fixed proton dose of 51015 cm2 with 5, 10, and 15 MeV irradiation energies was used in this study. For the dc characteristics, degradation was observed for sheet resistance, transfer resistance, contact resistivity, saturation drain current, maximum transconductance, reverse-bias gate leakage current, and sub-threshold drain leakage current for all the irradiated HEMTs; however, the degree of the degradation was decreased as the irradiation energy increased. Similar trends were obtained for the rf performance of the devices, with 10% degradation of the unity gain cut-off frequency (fT) and maximum oscillation frequency (fmax) for the HEMTs irradiated with 15 MeV protons but 30% for 5 MeV proton irradiation. The carrier removal rate was in the range 0.66 1.24 cm1 over the range of proton energies investigated.
    Journal of Vacuum Science & Technology B. 01/2012; 30(4).
  • [Show abstract] [Hide abstract]
    ABSTRACT: A finite element simulation was used to estimate the temperature distributions within AlGaN/GaN high electron mobility transistors (HEMTs) during the laser lift-off process. The time-dependent simulation showed that a thin layer of GaN at the GaN/sapphire interface was heated up to around 1600 K in less than 25 ns by a pulsed laser exposure with a duration of 25 ns and a fluence of 800 mJ/cm2 to decompose this GaN layer into Ga and nitrogen. Experimentally, there was a threshold fluence around 550 mJ/cm2, corresponding to 1300 K at the GaN/sapphire interface, for partially lifting off the HEMT structure from the sapphire. The simulated temperature at the GaN/sapphire interface with a fluence of 420 mJ/cm2 never reached above 1000 K, however, the HEMT structure was lifted-off by multiple laser exposures at this fluence. Therefore, instead of thermally induced decomposition, the lift-off mechanism could also be through the Ga–N bond breaking during the multiple lower-fluence high-energy 193 nm laser exposures.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(1):1203-.
  • [Show abstract] [Hide abstract]
    ABSTRACT: GaN-based light-emitting diodes (LEDs) were grown on a patterned sapphire substrate (PSS) containing hemispheres on the growth surface. Free-standing LED structures were obtained by removing the PSS using laser lift-off technique. The N-face GaN surface with micron-sized concave hemisphere structures, which had been located between the sapphire and the GaN film, was then exposed and photo-electrochemically etched using a 2M KOH solution to create nano-sized pyramids. Aluminum was deposited on the roughened N-face GaN as a reflective layer. The roughened aluminum reflectors, consisting of micron-sized hemisphere structures and nano-sized pyramids, enhanced the light extraction efficiency through multiple scattering events of photons and randomized the directions of the photons. The subsequent enhancement in electroluminescence was 13% compared with an untextured control LED.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2012; 30(5):050605-050605-4. · 1.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: When illuminated with below band-gap light, the response of the drain current of AlGaN/GaN High Electron Mobility Transistors (HEMTs) was measured. The energy of the wavelength of light corresponds to the trapping and de-trapping of carriers within the band-gap, providing an indicator of trap densities. These changes were compared on HEMTs with gate lengths of 0.14 & 0.17 μm, before and after electrically stressing under on-state (VG = 0 V), off-state (VG =-5 V), and typical operating conditions (VG = -2V) indicating a change in trap density as a result of electrical stressing, since the energy from a specific wavelength of light pumps traps whose activation energies are less than or equal to that of the light source. Changes in trap densities were minimal after both off-state and on-state stressing but significant trap creation in the range EC=-0.4-0.6 eV were observed in HEMTs exhibiting gradual degradation during stressing. Energy levels corresponding to these values in the literature have been suggested to correlate GaN and NGa substitutional defects, as well as GaI interstitials.
    Compound Semiconductor Integrated Circuit Symposium (CSICS), 2012 IEEE; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: AlGaN/GaN high electron mobility transistors (HEMTs) with similar active layers structures were grown on SiC or sapphire substrates using different buffer layer structures, including GaN of different thickness (1 or 2 μm) or composite AlGaN/GaN buffers. The highest density of hole traps was observed in the buffer on sapphire, while the lowest density of hole traps was obtained in the thick (2 μm) GaN buffer on SiC. The reverse leakage currents in HEMTs were lower in the devices grown on SiC substrates and the on-off ratios improved by two orders of magnitude for thicker GaN buffers or composite AlGaN/GaN buffers compared to a standard 1 μm GaN buffer. The maximum drain-source currents and tranconductances were all larger for the devices on SiC compared to sapphire.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(1):1205-.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Electrical properties and deep electron and hole trap spectra were measured for undoped n-GaN cut from a thick boule grown by hydride vapor phase epitaxy (HVPE). The material is characterized by a very low concentration of residual donors (1013–1014 cm-3) in the first 30 μm near the growth surface. The bulk electrical properties were similar to those of standard high quality undoped bulk HVPE n-GaN, with a net donor concentration of ∼1016 cm-3 and mobility ∼1000 cm2/V s. The strong decrease of electron concentration in the surface region of the high resistivity GaN was caused by the compensation of shallow residual donors by a high density (∼6 × 1015 cm-3) of hole traps with activation energy of 0.2 eV, confined to the compensated region. In addition, other hole traps H5 with activation energy 1.2 eV and concentration 5 × 1015 cm-3 were present. These latter traps had similar concentrations in both the high resistivity and standard conducting HVPE GaN. Radiation detectors prepared on the high resistivity material showed charge collection efficiency (CCE) close to 100% for spectrometry of α-particles with energy up to 5.1 MeV. The CCE dependence on voltage indicated a strong trapping of holes in the active region of detectors by the H5 hole traps.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(2):1205-.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O2) at room temperature. The monolayer graphene, grown by chemical vapor deposition (CVD) with perfect uniformity within 1cm×1cm will attach O2 molecules which will act as a p-type dopant and enhance the hole conductivity, make a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O2 concentration and the detection limit of the simple O2 sensor was 1.25% in volume ratio.
    Proc SPIE 01/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene layers on SiO2/Si substrates were exposed to chemicals or gases commonly used in semiconductor fabrication processes, including solvents (isopropanol, acetone), acids (HCl), bases (ammonium hydroxide), UV ozone, H2O and O2 plasmas. The recovery of the initial graphene properties after these exposures was monitored by measuring both the layer resistance and Raman 2D peak position as a function of time in air or vacuum. Solvents and UV ozone were found to have the least affect while oxygen plasma exposure caused an increase of resistance of more than 3 orders of magnitude. Recovery is accelerated under vacuum but changes can persist for more than 5 hours. Careful design of fabrication schemes involving graphene is necessary to minimize these interactions with common processing chemicals.
    Journal of Vacuum Science & Technology B. 01/2012; 30(4).
  • [Show abstract] [Hide abstract]
    ABSTRACT: Hydrothermally grown SnO2 was integrated with AlGaN/GaN high electron mobility transistor (HEMT) sensor as the gate electrode for oxygen detection. The crystalline of the SnO2 was improved after annealing at 400 C. The grain growth kinetics of the SnO2 nanomaterials, together with the O2 gas sensing properties and sensing mechanism of the SnO2 gated HEMT sensors were investigated. Detection of 1% oxygen in nitrogen at 100 C was possible. A low operation temperature and low power consumption oxygen sensor can be achieved by combining the SnO2 films with the AlGaN/GaN HEMT structure
    Journal of Vacuum Science & Technology B. 01/2012; 30(4).

Publication Stats

6k Citations
1,078.42 Total Impact Points

Institutions

  • 1994–2013
    • University of Florida
      • • Department of Materials Science and Engineering
      • • Department of Chemical Engineering
      Gainesville, Florida, United States
  • 2012
    • Kyungpook National University
      • School of Materials Science and Engineering
      Daikyū, Daegu, South Korea
  • 2009
    • Yale University
      • Department of Electrical Engineering
      New Haven, CT, United States
  • 2003–2009
    • Inje University
      • School of Nano Engineering
      South Korea
  • 2008
    • National Central University
      • Department of Optics and Photonics
      Taoyuan City, Taiwan, Taiwan
    • St. Petersburg College
      St. Petersburg, Florida, United States
  • 2002–2004
    • Wright-Patterson Air Force Base
      Dayton, Ohio, United States
  • 2001
    • Chonbuk National University
      • Semiconductor Physics Research Center
      Seoul, Seoul, South Korea
    • University of Central Florida
      • Department of Physics
      Orlando, FL, United States
  • 2000
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States
  • 1998
    • New Jersey Institute of Technology
      Newark, New Jersey, United States
  • 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