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14 Jul 2008

Volume 93, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 93, 023303 (2008); http://dx.doi.org/10.1063/1.2953179 (3 pages)

Takafumi Kawanishi, Takaaki Fujiwara, Megumi Akai-Kasaya, Akira Saito, Masakazu Aono, Junichi Takeya, and Yuji Kuwahara
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Impact of oxygen incorporation at the Si3N4/Al2O3 interface on retention characteristics for nonvolatile memory applications

Man Chang, Yongkyu Ju, Joonmyoung Lee, Seungjae Jung, Hyejung Choi, Minseok Jo, Sanghun Jeon, and Hyunsang Hwang

Appl. Phys. Lett. 93, 022101 (2008); http://dx.doi.org/10.1063/1.2957668 (3 pages) | Cited 7 times

Online Publication Date: 14 July 2008

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The correlation between properties of the Si3N4/Al2O3 interface and retention degradation was investigated for metal-alumina-nitride-oxide-silicon-type flash memory devices. The intermixed region near the Si3N4/Al2O3 interface showed an oxygen deficiency, which was confirmed by the binding energy of Al and Si peaks from x-ray photoelectron spectroscopy analysis. This oxygen deficiency led to the enhancement of trap-assisted tunneling current. Additional ambient oxygen annealing can eliminate the oxygen deficiency at the intermixed region, which in turn can significantly reduce charge loss through the blocking oxide. With the aim of better memory characteristics, oxygen incorporation shows promise for future nonvolatile memory applications.
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84.30.Sk Pulse and digital circuits
73.40.Gk Tunneling
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness

Detection of charge transfer processes in Cr-doped SrTiO3 single crystals

F. La Mattina, J. G. Bednorz, S. F. Alvarado, A. Shengelaya, and H. Keller

Appl. Phys. Lett. 93, 022102 (2008); http://dx.doi.org/10.1063/1.2959059 (3 pages) | Cited 14 times

Online Publication Date: 15 July 2008

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An insulator-to-metal transition is observed in Cr-doped SrTiO3 single crystals upon extended exposure to a high electric field, namely, electroconditioning (EC). Electron paramagnetic resonance (EPR) and transport measurements under laser irradiation show anticorrelation between the Cr3+ EPR signal and the electrical current. This proves that the Cr3+ ions are responsible for the photocurrent that initiates the EC process. We observe the presence of Cr3+/Cr4+ mixed valencies in the bulk in the conducting state. The EPR characterization of the spectra in the conducting state excludes the possibility of a Cr3+-oxygen vacancy complex in the bulk as a result of the EC.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
76.30.-v Electron paramagnetic resonance and relaxation
72.40.+w Photoconduction and photovoltaic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.28.+d Narrow-band systems; intermediate-valence solids

Modulated precursor flow epitaxial growth of AlN layers on native AlN substrates by metal-organic chemical vapor deposition

Hee Jin Kim, Suk Choi, Dongwon Yoo, Jae-Hyun Ryou, Russell D. Dupuis, R. F. Dalmau, P. Lu, and Z. Sitar

Appl. Phys. Lett. 93, 022103 (2008); http://dx.doi.org/10.1063/1.2959064 (3 pages) | Cited 10 times

Online Publication Date: 15 July 2008

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We have investigated the growth of AlN layers on bulk AlN substrates by modulated precursor flow epitaxial growth using metal-organic and hydride precursors as well as by conventional metal-organic chemical vapor deposition growth. A nanopit-containing morphology was observed for an AlN layer grown by conventional growth, while atomically smooth and pit-free surface was achieved for an AlN layer created by modulated precursor flow epitaxial growth. For similar growth set-point temperatures, nanopit-free surfaces were observed for AlN layers created by conventional growth on sapphire substrates. This is believed to be due to the difference in the temperature of the growing surface, as evidenced by finite element method thermal profiling and the morphology change of the AlN layer with decreasing temperature observed for growth of AlN on sapphire substrates. The AlN layers grown by modulated precursor flow epitaxial growth on the AlN bulk substrates also have excellent crystalline qualities with narrow x-ray rocking curve peak linewidths of 36 and 61 arc sec for the (002) and (102) diffraction conditions, respectively.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

High temperature stability of postgrowth annealed transparent and conductive ZnO:Al films

Burhan Bayraktaroglu, Kevin Leedy, and Robert Bedford

Appl. Phys. Lett. 93, 022104 (2008); http://dx.doi.org/10.1063/1.2959071 (3 pages) | Cited 19 times

Online Publication Date: 15 July 2008

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High temperature stability of Al-doped ZnO transparent thin films in air has been improved by a combination of optimized growth parameters and postgrowth treatment. Optical transparency was better than 90% for wavelengths ranging from 380 to at least 2500 nm with films that also had resistivities of 2×10−4 Ω cm. Depending on the growth conditions, film resistivities showed different degrees of increase in resistivity after storing in air at elevated temperatures. Films grown at lower pressures were stable up to 400 °C for short exposure times (2 h) and exhibited virtually no change in resistivity at 260 °C for over 2500 h.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments

(Zr,Hf)Co(Sb,Sn) half-Heusler phases as high-temperature (>700 °C) p-type thermoelectric materials

Slade R. Culp, J. W. Simonson, S. Joseph Poon, V. Ponnambalam, J. Edwards, and Terry M. Tritt

Appl. Phys. Lett. 93, 022105 (2008); http://dx.doi.org/10.1063/1.2959103 (3 pages) | Cited 26 times

Online Publication Date: 15 July 2008

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By substituting Sn for Sb, the potential of stable (Zr,Hf)Co(Sb,Sn) half-Heusler phases, as p-type thermoelectric materials, for high-temperature power generation has been examined. Sn concentration as much as ∼ 20%–30% is required to realize high power factor values. Substitution of heavier Hf, which reduces the thermal conductivity (κ) via mass fluctuation scattering, nonetheless maintains high mobility. As a result, the thermoelectric figure of merit ZT, for these not-yet-optimized materials, which we found to be ZT = 0.5 at 1000 K (measured) and ZT = 0.6 at 1100 K (extrapolated), surpasses the industry benchmark for a p-type material set by SiGe alloys.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.sd Impurity concentration
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Orientation of H platelets under local stress in Si

S. Reboh, M. F. Beaufort, J. F. Barbot, J. Grilhé, and P. F. P. Fichtner

Appl. Phys. Lett. 93, 022106 (2008); http://dx.doi.org/10.1063/1.2958212 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2008

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Hydrogen is implanted into (001) silicon under the strain field of previously formed overpressurized helium plates. Upon thermal annealing, the hydrogen atoms precipitate into platelet structures oriented within specific {111} or {001} variant determined through the local symmetry of the strain. The behavior is understood in terms of elastic interactions and is described via energy minimization calculations, predicting the formation and distribution of each platelet orientation variant. Our results demonstrate the concept that sublocal organized arrangements of precipitates can be obtained within nanosize domains using local strain fields.
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61.72.uf Ge and Si
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Electrical investigation of V-defects in GaN using Kelvin probe and conductive atomic force microscopy

A. Lochthofen, W. Mertin, G. Bacher, L. Hoeppel, S. Bader, J. Off, and B. Hahn

Appl. Phys. Lett. 93, 022107 (2008); http://dx.doi.org/10.1063/1.2953081 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2008

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We report on the electrical characterization of V-defects in GaN-based heterostructures via Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). The KPFM measurements show for n- and p-doped GaN top layers an increase in the work function within the V-defects. Surprisingly, an increase in the current flow within the V-defects is found by C-AFM in case of the n-doped structure, while current flow into the V-defect is suppressed for the p-doped structure. For a consistent explanation of these results we suggest a model, which is based on an increase in the electron affinity of the {10−11}-surfaces within the V-defects as compared to the planar (0001)-surface.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
68.47.Fg Semiconductor surfaces
68.37.Ps Atomic force microscopy (AFM)
61.72.uj III-V and II-VI semiconductors
68.35.bg Semiconductors

Transition layers at the SiO2/SiC interface

Tsvetanka Zheleva, Aivars Lelis, Gerd Duscher, Fude Liu, Igor Levin, and Mrinal Das

Appl. Phys. Lett. 93, 022108 (2008); http://dx.doi.org/10.1063/1.2949081 (3 pages) | Cited 25 times

Online Publication Date: 17 July 2008

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The electrical performance of SiC-based microelectronic devices is strongly affected by the densities of interfacial traps introduced by the chemical and structural changes at the SiO2/SiC interface during processing. We analyzed the structure and chemistry of this interface for the thermally grown SiO2/4H-SiC heterostructure using high-resolution transmission electron microscopy (TEM), Z-contrast scanning TEM, and spatially resolved electron energy-loss spectroscopy. The analyses revealed the presence of distinct layers, several nanometers thick, on each side of the interface; additionally, partial amorphization of the top SiC surface was observed. These interfacial layers were attributed to the formation of a ternary Si–C–O phase during thermal oxidation.
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68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Mq Oxidation

Germanium oxynitride (GeOxNy) as a back interface passivation layer for Germanium-on-insulator substrates

T. Signamarcheix, F. Allibert, F. Letertre, T. Chevolleau, L. Sanchez, E. Augendre, C. Deguet, H. Moriceau, L. Clavelier, and F. Rieutord

Appl. Phys. Lett. 93, 022109 (2008); http://dx.doi.org/10.1063/1.2960345 (3 pages) | Cited 1 time

Online Publication Date: 17 July 2008

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This paper describes the development of a GeOxNy surface passivation of germanium, which is mandatory for microelectronics germanium-on-insulator (GeOI) substrate fabrication. Indeed, germanium surface reactivity in ambient atmosphere requires the development of Ge surface passivation in order to provide an electrically acceptable interface between the active layer and the buried oxide (BOX) of GeOI substrates. In this paper, GeOI substrates with a passivation interlayer between the Ge film and the BOX were fabricated using the Smart Cut™ technology. Plasma treatments produced a germanium oxynitride (GeOxNy) passivation interlayer with a nitrogen concentration up to 40% and thickness of 3 nm. Electrical activity in such GeOI active layer was investigated with pseudo-metal-oxide-semiconductor field effect transistor measurements. Electron mobility reaches a value of 670 cm2 V−1 s−1, notably higher than those typically reported on nonpassivated GeOI structures.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Tv Field effect devices
81.65.Rv Passivation
72.20.Fr Low-field transport and mobility; piezoresistance

Long lifetimes in high-efficiency Cu(In,Ga)Se2 solar cells

Wyatt K. Metzger, Ingrid L. Repins, and Miguel A. Contreras

Appl. Phys. Lett. 93, 022110 (2008); http://dx.doi.org/10.1063/1.2957983 (3 pages) | Cited 21 times

Online Publication Date: 17 July 2008

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Time-resolved photoluminescence measurements on polycrystalline Cu(In,Ga)Se2 (CIGS) thin films corresponding to high-efficiency solar cells indicate recombination lifetimes as long as 250 ns, far exceeding previous measurements for this material. The lifetime decreases by two orders of magnitude when exposed to air. Charge separation effects can be observed on CIGS/CdS/ZnO devices in low-intensity conditions. The ZnO layer forms a robust junction critical for charge separation, whereas the CdS layer alone forms a much weaker junction. Recombination at the CIGS/CdS interface is negligible. The results significantly adjust the previous picture of recombination in CIGS solar cells.
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84.60.Jt Photoelectric conversion

High field electron dynamics in dilute nitride Ga(AsN)

S. Spasov, G. Allison, A. Patanè, L. Eaves, M. Yu. Tretyakov, A. Ignatov, M. Hopkinson, and G. Hill

Appl. Phys. Lett. 93, 022111 (2008); http://dx.doi.org/10.1063/1.2960547 (3 pages) | Cited 2 times

Online Publication Date: 17 July 2008

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We investigate the high electric field dynamics of conduction electrons in dilute nitride GaAs1−xNx diodes. At low temperature (T<40 K), we show that the trapping of hot electrons at localized states leads to low frequency oscillations (<1 Hz) of the current at high bias. This slow dynamics is replaced at higher temperatures by a fast response of the current in the subterahertz frequency range, which we relate to the interaction of hot electrons with resonant nitrogen-related states in the conduction band.
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85.30.Kk Junction diodes

Charge carrier induced lattice strain and stress effects on As activation in Si

Chihak Ahn and Scott T. Dunham

Appl. Phys. Lett. 93, 022112 (2008); http://dx.doi.org/10.1063/1.2956401 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2008

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We studied lattice expansion coefficient due to As using density functional theory with particular attention to separating the impact of electrons and ions. Based on As deactivation mechanism under equilibrium conditions, the effect of stress on As activation is predicted. We find that biaxial stress results in minimal impact on As activation, which is consistent with experimental observations by Sugii et al. [J. Appl. Phys. 96, 261 (2004) ] and Bennett et al. [J. Vac. Sci. Technol. B 26, 391 (2008) ].
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62.20.-x Mechanical properties of solids
61.72.Bb Theories and models of crystal defects
61.72.uf Ge and Si
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Bi Elemental solids

Dependence of ferromagnetic properties on conductivity for As-doped p-type (Zn0.93Mn0.07)O layers

Sejoon Lee, Yoon Shon, Tae Won Kang, Chong S. Yoon, Eun Kyu Kim, and Deuk Young Kim

Appl. Phys. Lett. 93, 022113 (2008); http://dx.doi.org/10.1063/1.2957027 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2008

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The As-doped p-type (Zn0.93Mn0.07)O layers show a strong dependence of their ferromagnetic properties on the hole conductivity that were controlled through the modification of negative background-charge density by changing the oxygen partial pressure during the initial growth stage before As doping. Curie temperature and spontaneous magnetization were observed to be increased as the hole conductivity increases. This result was confirmed to originate from stabilizations of incorporated Mn2+ ions and doped As acceptors, which can give rise to long-range ferromagnetic coupling.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
75.47.Pq Other materials
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