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23 Feb 2009

Volume 94, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 94, 082501 (2009); http://dx.doi.org/10.1063/1.3085971 (3 pages)

Chunghee Nam, B. G. Ng, F. J. Castaño, M. D. Mascaro, and C. A. Ross
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Strong field hole transport in 6H-SiC

V. I. Sankin, P. P. Shkrebiy, and R. Yakimova

Appl. Phys. Lett. 94, 082101 (2009); http://dx.doi.org/10.1063/1.3089233 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2009

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In materials with a small degree of ionicity ranging 10%–15%, such as in SiC, carrier scattering on polar optical potential is plausible. J-F characteristics of hot hole transport in 6H-SiC with Na−Nd ∼ 5×1017 cm−3 are studied at electrical fields of 1–150 kV/cm and temperatures from 300 to 600 K. In this work possible mechanisms contributing to the J-F characteristics are considered: scattering on ionized impurities, impurity breakdown due to Al acceptors, hole transport in the light valence subband formed due to splitting by crystal field, and dielectric breakdown related to polar optical scattering.
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72.20.Ht High-field and nonlinear effects
71.70.Ch Crystal and ligand fields
72.80.Jc Other crystalline inorganic semiconductors
77.22.Jp Dielectric breakdown and space-charge effects

Reversible changes of epitaxial thin films from perovskite LaNiO3 to infinite-layer structure LaNiO2

Masanori Kawai, Satoru Inoue, Masaichiro Mizumaki, Naomi Kawamura, Noriya Ichikawa, and Yuichi Shimakawa

Appl. Phys. Lett. 94, 082102 (2009); http://dx.doi.org/10.1063/1.3078276 (3 pages) | Cited 10 times

Online Publication Date: 24 February 2009

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An infinite-layer-structure epitaxial thin film of LaNiO2 was prepared by low-temperature reduction with CaH2 from a LaNiO3 epitaxial thin film grown on a SrTiO3(100) substrate. The oxygen content changed reversibly from the perovskite LaNiO3 to the infinite-layer LaNiO2 without losing the structural framework and the topotactic relationship. Consequently, the oxidation state of Ni ions in the film changed from trivalent to divalent to monovalent.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
82.30.-b Specific chemical reactions; reaction mechanisms

Pulse stress frequency dependence of negative bias temperature instability in SiON gate transistors

Jingfeng Yang, Jiaqi Yang, Baoguang Yan, Gang Du, Xiaoyan Liu, Ruqi Han, Jinfeng Kang, C. C. Liao, Z. H. Gan, M. Liao, J. P. Wang, and W. Wong

Appl. Phys. Lett. 94, 082103 (2009); http://dx.doi.org/10.1063/1.3079406 (3 pages) | Cited 1 time

Online Publication Date: 24 February 2009

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Dependence of negative bias temperature instability (NBTI) on the frequency of the pulsed stress applied on p-channel transistors with plasma nitrided SiON gate dielectrics is studied. The threshold voltage shift (ΔVth) decrease is observed with increase in frequency. The fractional relaxation is found to be more remarkable after a pulse stress with higher frequency. A phenomenological model based on the dispersive transport of hydrogen in the gate dielectrics is proposed to explain the pulse based NBTI characteristics. The frequency dependence of NBTI is attributed to the existence of deep level hydrogen traps in the gate dielectrics. The model predicts reduced frequency dependence in the ultrahigh frequency range. The results and discussion also confirm the overall correctness of the dispersive transport framework in interpreting the NBTI mechanisms.
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85.30.Tv Field effect devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

A low-cost method of forming epitaxy SiGe on Si substrate by laser annealing

C. Y. Ong, K. L. Pey, K. K. Ong, D. X. M. Tan, X. C. Wang, H. Y. Zheng, C. M. Ng, and L. Chan

Appl. Phys. Lett. 94, 082104 (2009); http://dx.doi.org/10.1063/1.3086881 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2009

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In this letter, a low-cost alternative for forming high grade silicon germanium (SiGe) by a laser-induced crystallization of an amorphous Ge layer deposited directly on Si+ preamorphized implantation Si substrate is demonstrated. The results show that a fully strained epitaxial SiGe layer on the Si (100) substrate can be obtained at laser fluence above the epitaxial threshold. This is due to a liquid-phase epitaxial regrowth process of the laser annealing induced melted layer. Below the epitaxial threshold, polycrystalline SiGe is formed due to explosive recrystallization process. Simultaneous boron activation is achieved with the SiGe formation, a result due to the high temperature induced by the laser annealing.
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81.05.Hd Other semiconductors
81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Lattice strain in bulk GaN epilayers grown on CrN/sapphire template

S. W. Lee, Jun-Seok Ha, Hyun-Jae Lee, Hyo-Jong Lee, H. Goto, T. Hanada, T. Goto, Katsushi Fujii, M. W. Cho, and T. Yao

Appl. Phys. Lett. 94, 082105 (2009); http://dx.doi.org/10.1063/1.3086890 (3 pages) | Cited 20 times

Online Publication Date: 24 February 2009

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Microphotoluminescence spectroscopy is used to investigate local strain in GaN films grown on c-sapphire with CrN buffer, where the CrN buffer is partly etched. Biaxial compressive strain dominates GaN films grown on CrN buffer/c-plane sapphire. The emission energies of D0X, FXA, and FXA-1LO emission lines shift gradually from a high value to a low one, as the excitation laser beam scans from the unetched side of the sample to the etched side, while the emission intensities show only a slight change. No cracking occurs in the GaN film during etching except a change in bending of the detached part of the GaN film from convex to concave as determined by surface profiler. Both the lattice parameter and the energy position of the bound exciton emission peaks from a completely detached GaN are almost the same as those reported for strain-free GaN. The line width of the (0002) ω scan of a GaN film is narrowed from 352 to 331 arc sec through detaching presumably due to decrease in bending. Those properties suggest that gradual lattice strain relaxation takes place in GaN layers grown on CrN buffer as etching of CrN buffer proceeds and that the chemical lift-off enables to detach a GaN film from a sapphire substrate without generating defects.
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81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
81.65.Cf Surface cleaning, etching, patterning
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

To change transport gap of semiconducting nanoparticles without disturbing the optical one: Core-shell approach

Bikas C. Das and Amlan J. Pal

Appl. Phys. Lett. 94, 082106 (2009); http://dx.doi.org/10.1063/1.3088861 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2009

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We show that transport gap of semiconducting nanoparticles can be changed without disturbing the optical gap. This is achieved through inorganic-organic hybrid core-shell approach. Different inorganic nanoparticles with a bandgap in the UV to NIR range are used as the core; as a shell to the nanoparticles, a monolayer of different organic molecules is used. With the inclusion of the shell layer, optical gap of the nanoparticles does not change. Transport gap, as obtained from current-voltage characteristics of a single nanoparticle with scanning tunneling microscope tip, changes to that of the shell-material irrespective of the bandgap of core nanoparticles.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors

Fabrication of graphene nanoribbon by local anodic oxidation lithography using atomic force microscope

S. Masubuchi, M. Ono, K. Yoshida, K. Hirakawa, and T. Machida

Appl. Phys. Lett. 94, 082107 (2009); http://dx.doi.org/10.1063/1.3089693 (3 pages) | Cited 39 times

Online Publication Date: 26 February 2009

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We conducted local anodic oxidation (LAO) lithography in single-layer, bilayer, and multilayer graphenes using tapping-mode atomic force microscope. The width of insulating oxidized area depends systematically on the number of graphene layers. An 800-nm-wide bar-shaped device fabricated in single-layer graphene exhibits the half-integer quantum Hall effect. We also fabricated a 55-nm-wide graphene nanoribbon (GNR). The conductance of the GNR at the charge neutrality point was suppressed at low temperature, which suggests the opening of an energy gap due to lateral confinement of charge carriers. These results show that LAO lithography is an effective technique for the fabrication of graphene nanodevices.
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81.16.Nd Micro- and nanolithography
81.65.Mq Oxidation
73.43.Lp Collective excitations
68.37.Ps Atomic force microscopy (AFM)
73.21.Ac Multilayers

Electronic properties of a metallic nanoparticle coupled to a graphene nanoribbon: A single-electron field effect transistor

M. Mizuno and Eugene H. Kim

Appl. Phys. Lett. 94, 082108 (2009); http://dx.doi.org/10.1063/1.3089819 (3 pages)

Online Publication Date: 26 February 2009

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The electronic properties of a metallic nanoparticle coupled to a graphene nanoribbon are discussed. Results for the nanoribbon’s electronic structure as well as the system’s transport properties are presented. This device is shown to behave as a field effect transistor operating at the single-electron level; its properties could be of utility in a variety of applications such as charge sensing and terahertz photonics.
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85.35.Gv Single electron devices
81.07.Bc Nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems

Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates

G. R. Yazdi, M. Beckers, F. Giuliani, M. Syväjärvi, L. Hultman, and R. Yakimova

Appl. Phys. Lett. 94, 082109 (2009); http://dx.doi.org/10.1063/1.3085958 (3 pages) | Cited 5 times

Online Publication Date: 27 February 2009

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A sublimation-recondensation process is presented for high quality AlN (0001) crystals at a high growth rate by employing 4H-SiC substrates with a predeposited epilayer. It is based on the coalescence of well oriented AlN microrods, which evolve from the apex of 2H-SiC pyramids grown out of hexagonal pits formed by thermal etching of the substrate during a temperature ramp up. This process yields stress-free 120-μm-thick AlN single crystals with a dislocation density as low as 2×106 cm−2.
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81.10.Bk Growth from vapor
81.65.Cf Surface cleaning, etching, patterning
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Study of boron diffusion in MgO in CoFeB∣MgO film stacks using parallel electron energy loss spectroscopy

Sankha S. Mukherjee, David MacMahon, Feiming Bai, Chih-Ling Lee, and Santosh K. Kurinec

Appl. Phys. Lett. 94, 082110 (2009); http://dx.doi.org/10.1063/1.3090035 (3 pages) | Cited 11 times

Online Publication Date: 27 February 2009

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Boron diffusion in MgO has been investigated in annealed film stacks of sputtered CoFeB∣MgO using transmission electron microscopy and parallel electron energy loss spectroscopy. The analyses show significant B movement when the films are annealed, with the formation of BOx complexes. Characteristic diffusion lengths have been estimated in films annealed at the commonly employed temperature range of 300–400 °C for the fabrication of magnetic tunnel junctions. An activation energy of 1.3 eV (±0.4 eV) has been extracted from these data that represent B diffusion in MgO through vacancies and defect states mediated by the formation of BOx complexes.
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68.35.Fx Diffusion; interface formation
79.20.Uv Electron energy loss spectroscopy
61.72.jd Vacancies
68.37.Og High-resolution transmission electron microscopy (HRTEM)
66.30.H- Self-diffusion and ionic conduction in nonmetals
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Pq Other materials
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