V. Krishnamoorthy

University of Florida, Gainesville, FL, United States

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Publications (32)63.41 Total impact

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    ABSTRACT: Scandium oxide was deposited epitaxially on (0001) GaN via gas-source molecular beam epitaxy (GSMBE) using elemental Sc and an electron cyclotron resonance (ECR) oxygen plasma. HXRD indicated that the Sc2O3 has a lower defect density than similarly prepared films of Gd2O3. The scandium oxide was atomically smooth, with a rms roughness of 0.5–0.8 nm, and was uniform in stoichiometry as measured by Auger electron spectroscopy (AES) depth profiling. An interface state density of mid 1011 eV—1 cm—2 was determined from capacitance–voltage profiling using the Terman method. This interface state density was roughly a factor of five lower than that obtained from similar diodes made from SiO2 on GaN.
    physica status solidi (a) 11/2001; 188(1):239 - 242. · 1.21 Impact Factor
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    ABSTRACT: The release of interstitials from extended defects after ion implantation acts as a driving force behind transient enhanced diffusion (TED). Implantation of Si + ions into regions of phosphorus-doped silicon provides experimental insight into the interaction of silicon interstitials and dopant atoms during primary damage annealing. The presence of phosphorus influences the morphology of secondary defects during initial nucleation. Transmission electron microscopy (TEM) is used to differentiate between defect types and quantify the interstitials trapped in extended defects. This analysis reveals that phosphorus results in a reduction of interstitials trapped in observable extended defects. The interstitial flux released from the implanted region is also affected by the phosphorus doping. This phenomenon is closely studied using secondary ion mass spectrometry (SIMS) to monitor diffusion enhancements of dopant layers. Shifts in diffused dopant profiles are correlated with the different morphologies of the extended defects and the decay of the silicon interstitial supersaturation. This correlation is used to understand the interaction of excess silicon interstitials with phosphorus atoms.
    01/2000;
  • Aaron D Lilak, Viswanath Krishnamoorthy, David Vieira, Mark Law, Kevin Jones
    MRS Proceedings. 01/2000; 610(1).
  • V. Krishnamoorthy, M. Puga Lambers, Kevin S. Jones
    Defect and Diffusion Forum 01/2000;
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    ABSTRACT: Boron, a p-type dopant, experiences transient enhanced diffusion (TED) via interstitials. The boron TED and {311} dissolution rates are explored as a function of implant energy dependence. Silicon implants of 1014/cm2 at various energies were used to damage the surface of a wafer with an epitaxially grown boron marker layer. Samples were annealed at 750 °C for 15-135 min to observe the diffusion exhibited by the marker layer and to correlate this with the dissolution of {311} type defects. The diffusion enhancement depends strongly on implant energy but the {311} dissolution rate is weakly dependent.
    Applied Physics Letters 01/2000; 77. · 3.79 Impact Factor
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    R. Raman, M. E. Law, V. Krishnamoorthy, K. S. Jones
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    ABSTRACT: The interactions between end-of-range dislocation loops and {311} defects as a function of their proximity were studied. The dislocation loops were introduced at 2600 Å by a dual 1×10<sup>15</sup>  cm <sup> -2 </sup>, 30 keV and a 1×10<sup>15</sup>  cm <sup> -2 </sup>, 120 keV Si <sup> + </sup> implantation into silicon followed by an anneal at 850 °C for 30 min. The depth of the loop layer from the surface was varied from 2600 to 1800 Å and 1000 Å by polishing off the Si surface using a chemical–mechanical polishing (CMP) technique. A post-CMP 1×10<sup>14</sup>  cm <sup> -2 </sup>, 40 keV Si <sup> + </sup> implantation was used to create point defects at the projected range of 580 Å. The wafers were annealed at 700, 800, and 900 °C, and plan-view transmission electron microscopy study was performed. It was found that the number of interstitials in {311} defects decreased as the projected range damage was brought closer to the loop layer, while the number of rectangular elongated defects (REDs) increased. Experimental investigation showed that REDs are formed at the end of range. It is concluded that the interstitials introduced at the projected range are trapped at the end of range. The REDs are formed due to the interactions between the interstitials and the pre-existing dislocation loops. © 1999 American Institute of Physics.
    Applied Physics Letters 03/1999; · 3.79 Impact Factor
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    R. Raman, M. E. Law, V. Krishnamoorthy, K. S. Jones, S. B. Herner
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    ABSTRACT: The effect of surface proximity on the dissolution of end-of-range dislocation loops in silicon was investigated by transmission electron microscopy (TEM). A layer of dislocation loops was formed at a depth of 2600 Å by annealing a Si wafer amorphized by a 1015 cm-2, 120 keV, and a 1015 cm-2, 30 keV dual Si+ implant for 30 min at 850 °C. The wafer was diced into 1 cm×1 cm pieces and polished by a chemical-mechanical polishing technique to decrease the loop depth to 1800 and 1000 Å. The samples were then furnace annealed at 900 and 1000 °C in N2 gas. Quantitative TEM analysis revealed that the density of small loops decreases as the loop band is brought closer to the surface. The flux of interstitials to the surface varied inversely with loop depth, indicating that the loop dissolution is diffusion limited. Assuming that the loops maintain a supersaturation of interstitials (CIL) around them, and by integrating the measured interstitial flux from the loop layer to the surface, the relative supersaturation of interstitials near the loop layer (CIL/CI*) was extracted 900 and 1000 °C.
    Applied Physics Letters 01/1999; 74. · 3.79 Impact Factor
  • R Raman, ME Law, V Krishnamoorthy, KS Jones
    Applied Physics Letters 01/1999; 74(5):700-702. · 3.79 Impact Factor
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    ABSTRACT: (001) CZ silicon wafers were implanted with As+ at 100 keV to a dose of 1×1015/cm2 in order to produce a continuous amorphous layer to a depth of about 120 nm. Furthermore, the implant condition was such that the peak arsenic concentration was below the arsenic clustering threshold. Subsequently, a second As+ or Ge+ implant was performed at 30 keV to doses of 2×1015/cm2, 5×1015/cm2 and 1×1016/cm2, respectively, into the as-implanted samples. All of the samples were annealed at 800 °C for 1 h. The second implant was designed to be contained within the amorphous region created by the initial implant. The second As+ implant was also designed to provide the additional arsenic needed to exceed the critical concentration for clustering at the projected range. Of the three samples with the dual As+ implant the clustering threshold was exceeded for the two lower doses while the SiAs precipitation threshold was exceeded at the highest dose. In the case of the dual As+/Ge+ implants the clustering and precipitation thresholds were not reached. Since arsenic and germanium are similar in mass the extent of damage created by these implants would be comparable. The implanted and annealed specimens were analyzed using secondary ion mass spectroscopy and transmission electron microscopy. The difference in the defect evolution and the transient-enhanced diffusion of arsenic beyond the end-of-range region between the As+ and Ge+ implanted and annealed samples was used to isolate the effects of arsenic clustering and precipitation. The results showed that point defects induced during clustering and/or precipitation did not contribute to the enhanced diffusion of arsenic although these defects did coalesce to form extended defects at the projected range. However, damage beyond the end-of-range region did cause enhanced diffusion of arsenic.
    Journal of Applied Physics 12/1998; 84(11). · 2.21 Impact Factor
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    ABSTRACT: Particulate coatings have wide ranging applications in several new technologies such as flat-panel displays, sintering of advanced ceramics, rechargeable batteries, etc. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Presently, laser ablation techniques have been primarily applied to deposit thin films on flat substrate materials. To deposit discontinuous particulate coatings, the laser induced plume from the target comes in contact with an agitated bed of core particles. The pressure and nature of the background gas (inert or active) controls the cluster size of the nano particles in the laser plume. Experiments were conducted for laser deposition of Ag nano particles on Al2O3 and SiO2 core particles by pulsed excimer laser (wavelength = 248 nm and pulse duration = 25 nanosecond) irradiation of a Ag sputtering target The surface coverage and coating uniformities of the film were found to depend on the synthesis parameters (energy density, # laser pulses, gas pressure backfill gas, molecular weight) as well as the residence time of the core particles in the plume regime. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), wavelength dispersive x-ray analysis (WDX), scanning transmission electron microscopy (STEM), and x-ray photoelectron spectroscopy (XPS).
    MRS Proceedings. 12/1997; 526.
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    ABSTRACT: The thermal stability of tellurium in InP has been examined in samples doped with Te up to an electron concentration of 1.4 × 1020 cm−3. Annealing was conducted using rapid thermal annealing for a period of one minute at temperatures over the range 650–800°C. Secondary ion mass spectroscopy analysis showed virtually no change in the Te profile before and after annealing, even at the highest annealing temperatures. High resolution x-ray diffraction and Hall measurements revealed a general decrease in the lattice strain and carrier concentration for annealing temperatures above 650°C. No evidence of strain relief was found in the form of cross-hatching or through the formation of a dislocation network as examined by scanning electron microscopy or transmission electron microscopy (TEM). These results are most likely due to the formation of Te clusters, though such clusters could not be seen by crosssectional TEM.
    Journal of Electronic Materials 10/1997; 26(11):1283-1286. · 1.64 Impact Factor
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    ABSTRACT: Titanium disilicide (TiSi2) films formed from varying compositions of co-deposited Ti and Si on a Si substrate and annealed in argon at 850°C have been characterized by Rutherford backscattering, Auger electron spectroscopy, transmission electron microscopy, atomic force microscopy, and high resolution X-ray diffraction. As-deposited films (TiSix) with x < 2 form a TiOxN1−x film on top of a TiSi2 film after annealing, while “Si-rich” (x > 2) film form TiSi2, with a poly Si film on top. This result is explained by the strong driving force of Ti to form an oxide or nitride with ambient gases while Si must diffuse through the growing film to form TiSi2. An “Si-rich” as-deposited composition (x > 2) results in less interface roughening between the TiSi2 film and Si substrate after annealing, as well as greater residual wafer curvature as compared to the other samples. The reduced wafer curvatures in the “Si-deficient” samples is attributed to the presence of the TiOxN1−x film which acts to counter the stress in the TiSi2 film.
    Thin Solid Films 06/1997; · 1.87 Impact Factor
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    ABSTRACT: Transient enhanced diffusion (TED) of boron in silica after low energy boron implantation and annealing was investigated using boron-doping superlattices (DSLs) grown by low temperature molecular beam epitaxy. Boron ions were implanted at 5, 10, 20, and 40 keV at a constant dose of 2×1014/cm2. Subsequent annealing was performed at 750 °C for times of 3 min, 15 min, and 2 h in a nitrogen ambient. The broadening of the boron spikes was measured by secondary ion mass spectroscopy and simulated. Boron diffusivity enhancement was quantified as a function of implant energy. Transmission electron microscopy results show that 〈311〉 defects are only seen for implant energies ⩾10 keV at this dose and that the density increases with energy. DSL studies indicate the point defect concentration in the background decays much slower when 〈311〉 defects are present. These results imply there are at least two sources of TED for boron implants (B-I): short time component that decays rapidly consistent with nonvisible B-I pairs and a longer time component consistent with interstitial release from the 〈311〉 defects. © 1997 American Institute of Physics.
    Journal of Applied Physics 02/1997; 81(4):1656-1660. · 2.21 Impact Factor
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    ABSTRACT: The effect of a thermally grown silicon nitride (SiNx) film on end-of-range extrinsic dislocation loops in a silicon substrate was investigated by transmission electron microscopy. A layer of extrinsic dislocation loops was formed by annealing a Si wafer amorphized by a Ge+ ion implant. A nitride film was grown on the Si by further annealing in ammonia (NH3) at 810 and 910 °C for 30–180 min. Wafers with a loop layer were also annealed in argon (Ar) at the same conditions as the NH3-annealed wafers to determine loop behavior in an inert environment. Samples annealed in NH3 had a significant decrease in the net number of interstitials bound by the loops, while those annealed in Ar showed no change. The results are explained by a supersaturation of vacancies caused by the presence of the nitride film, resulting in loop dissolution. By integrating the measured vacancy flux over the distance from the nitride/Si interface to the loop layer, we extract an estimate for the relative supersaturation of vacancies at 910 °C, CV/CV∗ ∼ 4, where CV is the concentration of vacancies and the asterisk denotes equilibrium. We rule out interstitial undersaturation-induced loop dissolution based on loop stability with temperature and oxidation-enhanced loop growth calculations. A comparison with estimated CV/CV∗ values from a previous report using the same processing equipment and parameters but monitoring the change in Sb diffusivity with nitridation shows excellent agreement.
    Journal of Applied Physics 01/1997; 81:7175-7180. · 2.21 Impact Factor
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    Jingwei Xu, V. Krishnamoorthy, Kevin S. Jones, Mark E. Law
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    ABSTRACT: Transient enhanced diffusion (TED) results from implantation damage creating enhanced diffusion of dopants in silicon. This phenomenon has mostly been studied using boron marker layers. We have performed an experiment using boron, phosphorus, and dislocation markers to compare TED effects. This experiment shows that phosphorus is enhanced significantly more than boron during damage annealing. Dislocation growth indicates that a number of interstitials greater than the damage dose is captured during these anneals. The time to saturate the dislocation growth agrees well with phosphorus diffusion saturation, and is greater than the boron saturation. © 1997 American Institute of Physics.
    Journal of Applied Physics 12/1996; 81(1):107-111. · 2.21 Impact Factor
  • V. Krishnamoorthy, B. Beaudet, K.S. Jones, D. Venables
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    ABSTRACT: Si wafers were implanted with As at energies ranging from 10-50 keV to a constant dose of 5e15/cm<sup>2</sup> and annealed at 700C for various times to study transient-enhanced-diffusion of arsenic and its correlation to the defect microstructure. The results showed that the diffusion enhancement was maximum after a 30 keV implant and anneal. The defect microstructure consisted of only end of range damage in the 10 and 20 keV specimens while the 30, 40 and 50 keV implanted/annealed specimens contained both end of range and projected range defects. An explanation for these observations is suggested, after taking into account a combination of factors that include arsenic precipitation, arsenic clustering and point defect annihilation at the surface
    Ion Implantation Technology. Proceedings of the 11th International Conference on; 07/1996
  • J. Liu, V. Krishnamoorthy, K.S. Jones, M.E. Law, J. Shi, J. Bennett
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    ABSTRACT: Si wafers were implanted with 20 keV boron ions to a dose of 2×10<sup>14</sup> cm<sup>-2</sup>. Subsequent anneals were performed in a nitrogen ambient at 650°C to 800°C for various times. The microstructures of the samples were examined using transmission electron microscopy (TEM). {311} defects were the only type of defects observed in all the samples. Transient enhanced diffusion (TED) behavior of boron atoms was studied using secondary ion mass spectrometry (SIMS). The diffusivity enhancement was calculated using FLOOPS simulations. The activation energy for the TED saturation process was determined to be 1.6 eV. Contributions of boron interstitial clusters and {311} defects to TED will be discussed
    Ion Implantation Technology. Proceedings of the 11th International Conference on; 07/1996
  • M. J. Matragrano, D. G. Ast, J. R. Shealy, V. Krishnamoorthy
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    ABSTRACT: We have investigated the strain relaxation of intentionally lattice mismatched (±0.5%) GaInP layers grown on GaAs substrates by organometallic vapor phase epitaxy. Double axis x‐ray diffraction was used to measure the relaxation in these epitaxial layers in perpendicular 〈110〉 directions as a function of thickness. For samples in tension, the difference in relaxation between [11¯0] and [110] increases from 10% to 48% as the layer thickness increases from 7 to 28 times the critical thickness, h c . For samples in compression this difference is 28% at 24h c while no relaxation is measured for a sample at 6h c . These results indicate that strain relaxes anisotropically and that the anisotropy is more pronounced for samples in tension than in compression. Furthermore, the major relaxation axis was found to be [11¯0] regardless of the sign of the strain. Reciprocal space maps, generated using triple axis x‐ray diffraction, showed that the amount of microtilt of the epitaxial layers was also anisotropic. This anisotropy and the direction of the maximum dislocation density which was measured by cathodoluminescence and transmission electron microscopy, changed from [110] in tension to [11¯0] in compression. The fact that the major relaxation axis remained stationary while the high misfit dislocation density direction rotated indicates that a substantial number of dislocations with Burgers vectors of the ‘‘wrong sense’’ for strain relief are formed in compressed epilayers. A model in which α type dislocations are more mobile than the β type misfit dislocations regardless of the sign of the strain is consistent with all of the experimental observations. © 1996 American Institute of Physics.
    Journal of Applied Physics 07/1996; · 2.21 Impact Factor
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    ABSTRACT: Transient enhanced diffusion of boron in preamorphized and subsequently regrown Si was studied by secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A comparison of 4 keV, 1× 10<sup>14</sup>/cm<sup>2</sup> boron implants into crystalline and Ge<sup>+</sup> preamorphized silicon was undertaken. Upon annealing the B<sup>+</sup> implant into crystalline material exhibited the well‐known transient enhanced diffusion (TED). In this case the peak of the boron distribution was relatively immobile and only B in the tail showed TED. In the second set of samples, the surface was first preamorphized by a 180 keV, 1×10<sup>15</sup>/cm<sup>2</sup> Ge<sup>+</sup> implant which produced an amorphous layer 2300 Å deep, which then was implanted with boron. After implantation the tail of the B distribution extended to only 700 Å. Upon annealing, TED of the boron in the regrown Si was also observed, but the diffusion profile was very different. In this case the peak showed no clustering, so the entire profile diffused. The time for the TED to decay was around 15 min at 800 °C. TEM results indicate that the (311) defects in the end of range damage finish dissolving between 10 and 60 min at 800 °C. These results indicate that for these Ge preamorphization conditions, not only do the end of range defects not block the flow of interstitials into the regrown silicon, the (311) defects in the end of range damage act as the source of interstitials. In addition, boron does not appear to cluster in regrown silicon. © 1996 American Institute of Physics.
    Applied Physics Letters 06/1996; · 3.79 Impact Factor
  • Solid-State Electronics 02/1996; 39(2):311–313. · 1.48 Impact Factor

Publication Stats

284 Citations
63.41 Total Impact Points

Institutions

  • 1991–1999
    • University of Florida
      • • Department of Electrical and Computer Engineering
      • • Department of Materials Science and Engineering
      Gainesville, FL, United States
  • 1994–1996
    • Cornell University
      • Department of Materials Science and Engineering
      Ithaca, NY, United States