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  • 1
    Electronic Resource
    Electronic Resource
    Control and analysis of leakage currents in poly-Si thin-film transistors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 895-904 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control of leakage current in autoregistered columnar and a solid phase crystallized poly-Si thin-film transistors (TFTs) is discussed. For n-channel TFTs, two parasitic leakage current paths, due to bulk conduction and back interface conduction, have been identified. It is demonstrated that these can be controlled by using sufficiently thin films and by low dose boron back channel implants, respectively. By these means, generation limited leakage currents, with values of 〈4×10−14 A/μm of channel width, have been obtained. The minimum leakage currents, for n- and p-channel TFTs, display the well-known field enhancement which we confirm can be described by phonon assisted tunneling. In well-engineered TFTs, with subthreshold slopes of 〈1 V/dec, we show that the drain fields required to promote the tunneling process are independent of the trap state density and result entirely from two-dimensional gate-drain coupling effects. Therefore, improving the quality of the poly-Si will not reduce the exponential dependence of the leakage current on gate and drain bias, although the absolute value of leakage current will be reduced. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360869
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of trapping states in polycrystalline-silicon thin film transistors by deep level transient spectroscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1787-1792 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline-silicon (poly-Si) thin film transistors (TFTs) have been assessed using deep level transient spectroscopy (DLTS) based on the measurement of current transients due to the thermal emission of carriers trapped at deep levels in the poly-Si. Measurements were made on fully hydrogenated TFTs and the DLTS signal was found to vary continuously between 77 K and room temperature, without showing the characteristic peaks normally associated with point defects in single crystal Si. This demonstrates the existence of a continuous distribution of states through the band gap rather than discrete monoenergetic states. Analysis of the DLTS signal suggests the density of states increases rapidly toward the conduction band edge indicating the presence of a relatively high density of tail states. After annealing the TFTs at 450 °C the current DLTS signal was found to increase due to an increase in trap state density, which occurs because Si–H bonds are thermally unstable at this temperature. The increase in signal was over the whole temperature range of the measurement showing that hydrogen passivates states up to at least 0.1 eV below the conduction band as well as states nearer mid-gap. The effects of varying the fill voltage on the measurement and the time dependence of the current transient were also investigated and added weight to arguments that the current transient was due to the thermal emission of carriers trapped at deep levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354782
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  • 3
    Electronic Resource
    Electronic Resource
    Electrically active defects in deep preamorphized single-crystal silicon layers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2702-2709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-energy Si and Ge implantations have been used to form thick (∼1 μm) amorphous films which permit direct electrical characterization of the layers after solid phase regrowth. The dislocation loops observed at the original amorphous–crystalline boundary after regrowth are fundamental to the preamorphization process and three dominant deep levels at Ec−0.40 eV, Ev + 0.47 eV, and Ev + 0.26 eV have been found to be spatially localized in the same region as the dislocation loops. The level at Ev+0.47 eV is most likely to be responsible for the spatially localized generation current also arising from the same region. The level at Ev+0.26 eV and a level, which was less dominant in the deep level transient spectroscopy measurements, at Ec−0.19 eV show features consistent with a defect displaying charge state controlled metastability. The density of these levels implied a high degree of reconstruction around the perimeter of the loops. The effects due to nitrogen decoration of the dislocations have also been investigated. The deep levels found within the regrown layers are believed to be associated with other dislocations which have not typically been seen in shallower preamorphized layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351042
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  • 4
    Electronic Resource
    Electronic Resource
    Deep levels of copper in silicon (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1826-1832 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect impurity levels have been examined in copper-diffused p-and n-type silicon using deep level transient spectroscopy. Levels at Ev+0.09, Ev+0.23, and Ev+0.42 eV have been observed in both types of material, although the deeper levels were only oberved in n-type material after post-diffusion annealing at 200 °C. Associated with the appearance of these levels in n-type material was another level at Ec−0.16 eV. This may be a further charge state of the center responsible for the Ev+0.23 eV and Ev+0.42 eV levels or the two centers may be decomposition products of a thermally unstable complex. Luminescence measurements have revealed the previously reported Cu-Cu spectrum in all the copper-diffused samples. The occurrence of this signal could not be correlated with the presence of the levels at Ev+0.23, Ev+0.42, or Ec−0.16 eV; this leaves the center at Ev+0.09 eV as the likely origin of the signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339564
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  • 5
    Electronic Resource
    Electronic Resource
    Defects and leakage currents in BF2-implanted preamorphized silicon (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3567-3575 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-dose silicon implants have been used to preamorphize the surface of single-crystal silicon prior to the implantation of low-energy BF2. The preamorphization results in shallow junction formation with minimal channeling of the boron, but high concentrations of electrically active defects are formed, leading to excessive reverse bias leakage currents. Measurements of leakage current and deep-level defects indicated that two distinct types of electrically active defects were important: those associated with what are probably complexes or clusters of point defects located near the far end of the range of the implanted silicon, and those associated with extended defects (loops) at the edge of the regrown amorphous region. The former defects were deep-level donors present in high concentrations (〉1017 cm−3) after regrowth of the amorphous layer at 600 or 700 °C and resulted in leakage currents 〉10−4 A/cm2. These centers could be annealed out at 800 °C reducing the leakage current to values between 5×10−8 and 2×10−5 A/cm2 depending upon the relative locations of the extended defects and the metallurgical junction. Measurements and modeling have shown that the location of the band of extended defects is critical in controlling the leakage current and that it will need to be a few hundred angstroms shallower than the junction itself for the associated generation current to be fully suppressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337613
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of electrical defects in Ge+ and Si+ preamorphized BF2-implanted silicon (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3628-3632 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon diode structures have been amorphized with 200-keV Ge+ prior to BF2 implantation. Room temperature C-V profiling revealed large concentrations of excess donor levels following epitaxial regrowth at temperatures below 800 °C. This donor formation and the annealing behavior is the same as previously observed in Si+ preamorphized substrates. Deep-level transient spectroscopy further confirmed the similarity in the nature and spatial distribution of the defects produced. The conclusion drawn is that the same fundamental damage-related defects are produced in the tail of the amorphizing implant in both cases. Large leakage current densities in the Ge+-amorphized diodes were attributed to the deep-level donors, and removal of these centers by annealing at 800 °C reduced the leakage current to ∼4×10−6 A/cm2. This current was assumed to arise from the crystallographic defects at the original amorphous/crystalline boundary which, at the ion implantation energies used, were within the zero-bias space-charge layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339266
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of melt depth in laser crystallized poly-Si thin film transistors (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4086-4094 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of film thickness and incident excimer laser energy density on the properties of poly-Si thin film transistors has been investigated and a coherent pattern of behavior has been identified which establishes controlled melt-through of the film as a key condition for achieving high quality devices. The conditions were correlated with the appearance of large grains and gave consistent results from both n- and p-channel devices, with carrier mobilities of more than 150 and 80 cm2/V s, respectively, and leakage currents of less than 2×10−14 A/μm. From a study of static irradiations, using a semi-Gaussian laser beam, the results are shown to be consistent with the super lateral grain growth (SLG) model. The trailing edge of the beam, when used in a swept mode, has been demonstrated to play an important role in extending the size of the energy window for this effect by re-setting the material into the SLG regime. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365719
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  • 8
    Electronic Resource
    Electronic Resource
    Defects in preamorphized single-crystal silicon (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2214-2216 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct electrical characterization of 1-μm-thick Si+ preamorphized and epitaxially regrown silicon layers has revealed a low concentration of residual deep-level defects within the regrown layer. A deep-level trap at Ec −0.40 eV has been found associated with the amorphous-crystalline boundary dislocation loops. In addition, a near mid-gap trap at Ev+0.54 eV, observed in p-type samples, is believed to be responsible for a spatially localized generation current of ∼2×10−6 A/cm2 associated with the dislocation loops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103895
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