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  • 1
    Electronic Resource
    Electronic Resource
    Photocapacitance study of bulk deep levels in ZnSe grown by molecular-beam epitaxy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 730-738 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of initial growth conditions and lattice matching on the deep level spectrum of n-ZnSe grown on GaAs by molecular-beam epitaxy is investigated by means of deep level optical spectroscopy. A detailed study of both the steady-state and transient photocapacitance allows us to measure optical threshold energies, concentrations, and emission rates of electronically active defects in the ZnSe layer. Several deep levels are found in the ZnSe layer at Ec−Et=1.15, 1.46, 1.90, and 2.25 eV with concentrations in the 1012–1014 cm−3 range. When a 2-nm-thick composition controlled interface layer is grown at different beam pressure ratios prior to the ZnSe growth, a distinct decrease in the 1.46 eV level concentration with increasing Se content is found. Deposition of a lattice-matched InxGa1−xAs buffer layer prior to the ZnSe growth reduces the concentration of both the 1.15 and 1.46 eV levels by over an order of magnitude, indicating the role of lattice matching in the ZnSe overlayer. We also perform depth profiling of the defect distributions within the ZnSe overlayer to see the effect of the ZnSe thickness on the concentration of these levels as well as their possible association to the ZnSe/GaAs interface. We find that only the 2.25 eV level concentration shows a dependence on depth, increasing as the II–VI/III–V interface is approached. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371933
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  • 2
    Electronic Resource
    Electronic Resource
    Second harmonic generation from trinitro-substituted subphthalocyanines films: Evidence of noncentrosymmetric molecular organization (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1802-1804 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Second-harmonic generation from λ=1.06 μm fundamental light has been measured in both evaporated and spin-coated films of trinitro-substituted subphthalocyanines. Ordering of these noncentrosymmetric molecules with the dipole moment perpendicular to the film face has been achieved either by the deposition process (evaporated samples) or by corona poling (spin-coated samples). The second-order susceptibilities χ31(2)=2.36×10−9 esu (for vacuum evaporated samples) and χ31(2)=9.62×10−10–1.14×10−9 esu (for poled spin-coated samples) have been determined by comparison with an X-cut LiNbO3 crystal used as reference. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118696
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  • 3
    Electronic Resource
    Electronic Resource
    Evidence for a dominant midgap trap in n-ZnSe grown by molecular beam epitaxy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 832-834 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A midgap deep level in n-type ZnSe grown by molecular beam epitaxy (MBE) on In0.04Ga0.96As/GaAs is detected and investigated by deep level optical spectroscopy and cathodoluminescence spectroscopy. The deep level has an optical threshold energy of 1.46 eV below the conduction band edge, and its concentration strongly depends on the Zn:Se beam pressure ratio during initial nucleation of the ZnSe layer. The concentration of this level decreases by a factor of ∼8 for Se rich vs Zn rich nucleation conditions, correlating with a decrease in the Se vacancy concentration for Se-rich nucleation. The investigation of photocapacitance transients revealed a strong interaction of the 1.46 eV level with both the conduction and the valence bands. Moreover, this level showed the largest optical cross section (emission rate of ∼103 s−1) of all of the levels found in the ZnSe layer. Taken together, these observations suggest this level may be an important recombination-generation center in MBE-grown ZnSe devices on GaAs substrates. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124528
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrogen passivation of deep levels in n–GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1499-1501 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differential postgrowth hydrogen passivation of deep levels in n–GaN grown by metal-organic chemical vapor deposition has been directly observed by means of both deep level transient spectroscopy and deep level optical spectroscopy. Two deep levels found at Ec−Et=0.62 and 1.35 eV show strong H passivation effects, with their concentrations decreasing by a factor of ≥30 and ∼14, respectively. The decrease in the 0.62 eV trap concentration together with its correlation with the presence of Mg in n–GaN is consistent with Mg–H complex formation. A band of closely spaced deep levels observed at Ec−Et=2.64–2.80 eV narrows to Ec−Et=2.74–2.80 eV after hydrogenation, consistent with hydrogen complexing with VGa3− defects as anticipated by earlier theoretical results. Finally, a deep level at Ec−Et=3.22 eV likely related to background acceptors remains unaffected by hydrogen. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290042
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  • 5
    Electronic Resource
    Electronic Resource
    Optically and thermally detected deep levels in n-type Schottky and p+-n GaN diodes (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3064-3066 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: N-Schottky and p+–n GaN junctions are currently used for different technologies. A comparison of the deep levels found throughout the entire band gap of n-GaN grown by metal-organic chemical vapor deposition under both configurations is presented. Both deep level optical spectroscopy and deep level transient spectroscopy measurements are used allowing the observation of both majority and minority carrier traps. Deep levels at Ec−Et=0.58–0.62, 1.35, 2.57–2.64, and 3.22 eV are observed for both diode configurations, with concentrations in the ∼1014–1016 cm−3 range. The 0.58–0.62 eV level appears correlated with residual Mg impurities in the n side of the p+–n diode measured by secondary-ion-mass spectroscopy, while the 1.35 eV level concentration increases by a factor of ∼4 for the Schottky junction possibly correlating with the carbon profile. The 2.57–2.64 eV level is a minority carrier hole trap in n-GaN, likely related to the yellow photoluminescence band, and is detected both optically from the conduction band (2.64 eV) and thermally from the valence band (0.87 eV). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126580
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  • 6
    Electronic Resource
    Electronic Resource
    Impact of Ga/N flux ratio on trap states in n-GaN grown by plasma-assisted molecular-beam epitaxy (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 805-807 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of growth regime on the deep level spectrum of n-GaN using molecular-beam epitaxy (MBE) was investigated. As the Ga/N flux ratio was decreased towards Ga-lean conditions, the concentration of two acceptor-like levels, at Ec−3.04 and 3.28 eV, increased from 1015 to 1016 cm−3 causing carrier compensation in these films. Thus, these two traps behaved as the dominant compensating centers in MBE n-GaN. Furthermore, the increase in trap concentration also strongly correlated with the degradation of both surface morphology and bulk electron mobility towards Ga-lean conditions, where higher pit densities and lower mobility were observed. These results show that the growth regime directly impacts all morphology, bulk transport, and trap states in n-GaN. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1445274
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