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21 Dec 2009

Volume 95, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 251105 (2009); http://dx.doi.org/10.1063/1.3275666 (3 pages)

D. Stehr, C. M. Morris, D. Talbayev, M. Wagner, H. C. Kim, A. J. Taylor, H. Schneider, P. M. Petroff, and M. S. Sherwin
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Demonstration of Raman gain at 800 nm in single-mode fiber and its potential application to biological sensing and imaging

Keisuke Goda, Ata Mahjoubfar, and Bahram Jalali

Appl. Phys. Lett. 95, 251101 (2009); http://dx.doi.org/10.1063/1.3275739 (3 pages) | Cited 2 times

Online Publication Date: 21 December 2009

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Optical amplification prior to photon-to-electron conversion improves detection sensitivity in spectroscopic and imaging applications. Here we report the first experimental demonstration of Raman amplification in a single-mode fiber at wavelengths near 800 nm. This approach can potentially enable fast real-time optical sensing and imaging in the wavelength band that benefits from both low water absorption and the availability of high-power Ti:Sapphire lasers.
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87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics
42.81.Pa Sensors, gyros
42.55.Wd Fiber lasers

Enhanced photoluminescence of strained Ge with a δ-doping SiGe layer on silicon and silicon-on-insulator

Cheng Li, Yanghua Chen, Zhiwen Zhou, Hongkai Lai, and Songyan Chen

Appl. Phys. Lett. 95, 251102 (2009); http://dx.doi.org/10.1063/1.3275863 (3 pages) | Cited 5 times

Online Publication Date: 21 December 2009

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An enhancement of the direct bandgap photoluminescence from Ge layer on silicon with boron or phosphorous δ-doping SiGe layers at room temperature is reported. The n-type δ-doping SiGe layer is proposed to transfer extra electrons to L valley in Ge, which decreases the possibility of the excited electrons in the Γ valley to be scattered to the L valley, and improve the photoluminescence of the direct band transition in the Ge layer. Additionally, 2.5 fold enhancement of luminescence from the strained Ge layer on a silicon-on-insulator substrate is demonstrated due to the resonant effect. This investigation is very promising for efficient Si-based Ge light emitting diodes compatible with silicon technology.
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78.66.-w Optical properties of specific thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
78.55.-m Photoluminescence, properties and materials
85.60.Jb Light-emitting devices

Emission wavelength tuning of interband cascade lasers in the 3–4 μm spectral range

A. Bauer, F. Langer, M. Dallner, M. Kamp, M. Motyka, G. Sęk, K. Ryczko, J. Misiewicz, S. Höfling, and A. Forchel

Appl. Phys. Lett. 95, 251103 (2009); http://dx.doi.org/10.1063/1.3270002 (3 pages) | Cited 7 times

Online Publication Date: 21 December 2009

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GaSb-based type-II quantum well (QW) structures and interband cascade lasers (ICLs) are investigated with regards to the dependence of emission wavelength on active QW thicknesses. Experimentally derived photoluminescence data and electrically driven ICL device data accompanied by theoretical calculations yield an average tuning rate of 0.55 μm per monolayer InAs in the range between 2.97 and 4.16 μm. Together with a temperature dependent ICL tuning behavior of 1.88 nm/K, the presented results provide the means for reliable and accurate emission wavelength control of ICLs in the 3–4 μm wavelength span which is of major importance for gas sensing applications.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Tuning micropillar cavity birefringence by laser induced surface defects

Cristian Bonato, Dapeng Ding, Jan Gudat, Susanna Thon, Hyochul Kim, Pierre M. Petroff, Martin P. van Exter, and Dirk Bouwmeester

Appl. Phys. Lett. 95, 251104 (2009); http://dx.doi.org/10.1063/1.3276550 (3 pages) | Cited 6 times

Online Publication Date: 22 December 2009

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We demonstrate a technique to tune the optical properties of micropillar cavities by creating small defects on the sample surface near the cavity region with an intense focused laser beam. Such defects modify strain in the structure, changing the birefringence in a controllable way. We apply the technique to make the fundamental cavity mode polarization-degenerate and to fine tune the overall mode frequencies, as needed for applications in quantum information science.
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42.55.Sa Microcavity and microdisk lasers
42.50.Pq Cavity quantum electrodynamics; micromasers
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Ultrafast carrier capture in InGaAs quantum posts

D. Stehr, C. M. Morris, D. Talbayev, M. Wagner, H. C. Kim, A. J. Taylor, H. Schneider, P. M. Petroff, and M. S. Sherwin

Appl. Phys. Lett. 95, 251105 (2009); http://dx.doi.org/10.1063/1.3275666 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2009

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To explore the capture dynamics of photoexcited carriers in semiconductor quantum posts, optical pump terahertz (THz) probe and time-resolved photoluminescence spectroscopy were performed. The results of the THz experiment show that after ultrafast excitation, electrons relax within a few picoseconds into the quantum posts, which act as efficient traps. The saturation of the quantum post states, probed by photoluminescence, was reached at approximately ten times the quantum post density in the samples. The results imply that quantum posts are highly attractive nanostructures for future device applications.
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73.63.Kv Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.47.jd Time resolved luminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors

Surface plasmon lasers with quantum dots as gain media

A. Banerjee, R. Li, and H. Grebel

Appl. Phys. Lett. 95, 251106 (2009); http://dx.doi.org/10.1063/1.3276273 (3 pages) | Cited 6 times

Online Publication Date: 22 December 2009

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As surface plasmons waveguides enter the electronic circuitry, surface plasmon (SP) sources are required. Here we demonstrate following attributes of optically pumped SPs laser: threshold, gain, spectral line narrowing, and feedback at 630 nm. The distinction between these attributes and those exhibited by amplified spontaneous emission source are discussed.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
42.79.Gn Optical waveguides and couplers
42.55.Px Semiconductor lasers; laser diodes

Terahertz metamaterials fabricated by inkjet printing

Markus Walther, Alex Ortner, Henning Meier, Ute Löffelmann, Patrick J. Smith, and Jan G. Korvink

Appl. Phys. Lett. 95, 251107 (2009); http://dx.doi.org/10.1063/1.3276544 (3 pages) | Cited 22 times

Online Publication Date: 23 December 2009

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Metamaterial layers designed for gigahertz to terahertz (THz)-frequencies have been fabricated by inkjet printing. The spectral response of the structures consisting of periodically arranged metallic split-ring resonators is characterized by THz-time-domain spectroscopy and compared with identical structures produced by conventional photolithography and etching techniques. The broader linewidth of their resonances is shown to originate mainly from structural inhomogeneities. Our study shows that inkjet printing is a viable route for producing metamaterial structures, allowing for rapid processing and flexibility in the choice of substrates.
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84.40.Az Waveguides, transmission lines, striplines
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Hybrid states of Tamm plasmons and exciton polaritons

M. Kaliteevski, S. Brand, R. A. Abram, I. Iorsh, A. V. Kavokin, and I. A. Shelykh

Appl. Phys. Lett. 95, 251108 (2009); http://dx.doi.org/10.1063/1.3266841 (3 pages) | Cited 10 times

Online Publication Date: 23 December 2009

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Channeling of exciton polaritons in the plane of semiconductor microcavities can be achieved by the deposition of metallic mesas on the top of the semiconductor structure. We show theoretically that the regime of strong coupling between cavity polaritons and Tamm surface plasmons is possible in such structures. The effect is favorable for the spatial confinement of polaritons and the formation of hybrid one-dimensional plasmon-polariton modes.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.22.Lp Collective excitations

Study of laser-plasma interaction using a physics-based model for understanding the physical mechanism of double-pulse effect in nanosecond laser ablation

Benxin Wu, Yun Zhou, and Andrew Forsman

Appl. Phys. Lett. 95, 251109 (2009); http://dx.doi.org/10.1063/1.3276695 (3 pages) | Cited 1 time

Online Publication Date: 23 December 2009

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This paper studies the double-pulse effect in high-intensity ( ≥ ∼ GW/cm2) nanosecond (ns) laser ablation, which refers to the significant material removal rate enhancement for ablation by two ns laser pulses (often separated by a delay time of ∼ 10 to 100 ns). The early-stage interaction of the second laser pulse with the plasma plume created by the first pulse is very important for understanding the physical mechanism of the double pulse effect. However, the plasma properties in the early stage (during a laser pulse or within 20 to 30 ns after the completion of the pulse) are very difficult to measure experimentally. In this letter, a physics-based predictive model is used as the investigation tool, which was previously verified based on experiments on plasma properties in the late stage, which are relatively easy to measure. The study shows that the second laser pulse does not directly strike the target condensed phase. Instead, it mainly interacts with the plasma plume created by the first laser pulse, heats and accelerates the ablated material in the plume lingering above the target surface.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
52.25.-b Plasma properties

Ultrahigh contrast light valve driven by electrocapillarity of liquid gallium

Jeff T. H. Tsai, Chih-Ming Ho, Fu-Cheng Wang, and Chi-Te Liang

Appl. Phys. Lett. 95, 251110 (2009); http://dx.doi.org/10.1063/1.3278441 (3 pages) | Cited 2 times

Online Publication Date: 23 December 2009

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This letter describes an ultrahigh contrast valve driven by the electrocapillarity of liquid gallium. We demonstrate that a micrometer-sized gallium droplet can be used to fabricate a prototype backlight transmissive pixel cell by transforming the droplet into a flat thin film. This light valve exhibits significantly high backlight utility (96%), an exceptional contrast ratio (106:1), and fast response time (0.49 ms). The high contrast ratio originated from the exceptional reflectivity of gallium, which can block backlight to prevent any transmission in the off state of our device. Without using any polarizer, the backlight utility can be improved dramatically compared to a conventional liquid crystal display. The backlight utility and switching time obtained from this prototype light valve is higher than that of commercial liquid crystal displays. This concept is also applicable to a wide variety of electro-optical devices.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Two-color quantum dot laser with tunable wavelength gap

S. G. Li, Q. Gong, Y. F. Lao, H. D. Yang, S. Gao, P. Chen, Y. G. Zhang, S. L. Feng, and H. L. Wang

Appl. Phys. Lett. 95, 251111 (2009); http://dx.doi.org/10.1063/1.3278594 (3 pages) | Cited 8 times

Online Publication Date: 23 December 2009

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We report on two-color InAs/InP(100) quantum dot lasers with tunable wavelength gap. Two peaks of lasing emission were observed simultaneously, while the high energy peak undergoes continuous blueshift with the increase in the injection current, and the low energy peak is somewhat fixed. Sophisticated studies of the wavelength gap as a function of the laser power prove that the two-peak lasing and shifting is not caused by the effect of Rabi oscillation. Moreover, comparison of electroluminescence and lasing spectra under different injection currents reveal the blueshift of the high energy peak is most likely related to the state-filling effect.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Plume composition control in double pulse ultrafast laser ablation of metals

Salvatore Amoruso, Riccardo Bruzzese, and Xuan Wang

Appl. Phys. Lett. 95, 251501 (2009); http://dx.doi.org/10.1063/1.3276690 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2009

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Ultrafast laser ablation of a metallic target induced by a pair of identical laser pulses temporally delayed from ≈ 1 to 2000 ps was studied by optical emission spectroscopy, imaging, and ion probe. Our experimental results demonstrate that plume excitation/ionization enhancement or nanoparticles reduction is achieved by properly delaying the two pulses. This possibility of controlling plume composition via an efficient coupling of the energy of the second pulse to the various ablation components produced by the first pulse is of particular interest in the process of material deposition and film growth.
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81.05.Bx Metals, semimetals, and alloys
78.47.J- Ultrafast spectroscopy (<1 psec)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
78.66.Bz Metals and metallic alloys
68.55.at Other materials
81.15.Fg Pulsed laser ablation deposition
78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Magnetohydrodynamic energy conversion by using convexly divergent channel

Tomoyuki Murakami and Yoshihiro Okuno

Appl. Phys. Lett. 95, 251502 (2009); http://dx.doi.org/10.1063/1.3272014 (3 pages) | Cited 3 times

Online Publication Date: 23 December 2009

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We describe a magnetohydrodynamic (MHD) electrical power generator equipped with a convexly divergent channel, as determined through shock-tunnel-based experiments. The quality of MHD power-generating plasma and the energy conversion efficiency in the convexly divergent channel are compared with those from previous linearly divergent channel. The divergence enhancement in the channel upstream is effective for suppressing an excessive increase in static pressure, whereby notably high isentropic efficiency is achieved.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
84.60.Lw Magnetohydrodynamic conversion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
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On the symmetry of the morphotropic phase boundary in ferroelectric BiScO3–PbTiO3 system

K. Datta, S. Gorfman, and P. A. Thomas

Appl. Phys. Lett. 95, 251901 (2009); http://dx.doi.org/10.1063/1.3268478 (3 pages) | Cited 2 times

Online Publication Date: 21 December 2009

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A single crystal of (1−x)BiScO3−xPbTiO3 at x = 0.64, which is the morphotropic phase boundary composition for this system, has been investigated utilizing two different types of diffractometry. A total of twenty different reciprocal space maps for different Bragg reflections {hkl} were collected to study their individual splittings. It has been shown that to explain the 2θ splittings observed, a two-phase model is necessary. The best model found consists of either two primitive orthorhombic or two primitive monoclinic lattices and the models previously proposed based on powder diffraction data, consisting rhombohedral or tetragonal symmetries, can be rejected.
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77.84.Cg PZT ceramics and other titanates
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Altering the nucleation of thermally annealed hydrogenated amorphous silicon with laser processing

M. S. Dabney, P. A. Parilla, L. M. Gedvilas, A. H. Mahan, and D. S. Ginley

Appl. Phys. Lett. 95, 251902 (2009); http://dx.doi.org/10.1063/1.3259654 (3 pages) | Cited 3 times

Online Publication Date: 22 December 2009

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We demonstrate the use of laser processing to affect the nucleation of crystallites in thermally annealed hydrogenated amorphous silicon (a-Si:H) thin films. The influence of film H content and subcrystallization threshold laser fluence are investigated by x-ray diffraction measurements during in situ thermal annealing at 600 °C. All laser-treated films show a reduced incubation time for crystallization compared to as-grown films, with the largest differences exhibited for samples with higher film H and higher laser fluences. These results are consistent with multivacancy annihilation by laser processing, based upon a recently developed model for a nucleation center in a-Si:H.
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68.55.A- Nucleation and growth
64.60.Q- Nucleation
81.40.Gh Other heat and thermomechanical treatments
81.05.Gc Amorphous semiconductors

Solid-state dewetting of patterned thin films

Donghyun Kim, Amanda L. Giermann, and Carl V. Thompson

Appl. Phys. Lett. 95, 251903 (2009); http://dx.doi.org/10.1063/1.3268477 (3 pages) | Cited 22 times

Online Publication Date: 22 December 2009

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Gold particle arrays have been produced through solid-state dewetting of patterned gold thin films. Patterns included rectangles and terminated lines of different widths, lengths, and film thickness. The particle spacing in long lines followed a Rayleigh-like dependence on the cross-sectional area of the line. Shorter lines had lower numbers of particles, indicating line-end effects. In some cases, ordered particle arrays were obtained. The probability of forming ordered particle arrays was shown to depend on the relative magnitudes of the length, width, and thickness of patterned structures. These trends are captured in design maps.
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68.55.J- Morphology of films
68.08.Bc Wetting
68.55.jd Thickness

Tactile objects based on an amplitude disturbed diffraction pattern method

Yuan Liu, Jean-Pierre Nikolovski, Nazih Mechbal, Moustapha Hafez, and Michel Vergé

Appl. Phys. Lett. 95, 251904 (2009); http://dx.doi.org/10.1063/1.3276549 (3 pages)

Online Publication Date: 23 December 2009

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Tactile sensing is becoming widely used in human-computer interfaces. Recent advances in acoustic approaches demonstrated the possibilities to transform ordinary solid objects into interactive interfaces. This letter proposes a static finger contact localization process using an amplitude disturbed diffraction pattern method. The localization method is based on the following physical phenomenon: a finger contact modifies the energy distribution of acoustic wave in a solid; these variations depend on the wave frequency and the contact position. The presented method first consists of exciting the object with an acoustic signal with plural frequency components. In a second step, a measured acoustic signal is compared with prerecorded values to deduce the contact position. This position is then used for human-machine interaction (e.g., finger tracking on computer screen). The selection of excitation signals is discussed and a frequency choice criterion based on contrast value is proposed. Tests on a sandwich plate (liquid crystal display screen) prove the simplicity and easiness to apply the process in various solids.
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62.65.+k Acoustical properties of solids

Partial strain relaxation via misfit dislocation generation at heterointerfaces in (Al,In)GaN epitaxial layers grown on semipolar (11math2) GaN free standing substrates

Anurag Tyagi, Feng Wu, Erin C. Young, Arpan Chakraborty, Hiroaki Ohta, Rajaram Bhat, Kenji Fujito, Steven P. DenBaars, Shuji Nakamura, and James S. Speck

Appl. Phys. Lett. 95, 251905 (2009); http://dx.doi.org/10.1063/1.3275717 (3 pages) | Cited 36 times

Online Publication Date: 23 December 2009

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Misfit strain relaxation via misfit dislocation (MD) generation was observed in heteroepitaxially grown (Al,In)GaN layers on free-standing semipolar (11math2) GaN substrates. Cross-section transmission electron microscope images revealed MD arrays at alloy heterointerfaces, with the MD line direction and Burgers vector parallel to [1math00] and [11math0], respectively. The MD structure is consistent with plastic relaxation by dislocation glide on the (0001) plane. Since (0001) is the only slip plane, the plastic relaxation is associated with tilt of the epitaxial (Al,In)GaN layers. The tilt, measured via high-resolution x-ray diffraction, can be used to quantify the relaxation.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.ag Semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Atomic structure evolution in bulk metallic glass under compressive stress

G. Wang, N. Mattern, S. Pauly, J. Bednarčik, and J. Eckert

Appl. Phys. Lett. 95, 251906 (2009); http://dx.doi.org/10.1063/1.3276274 (3 pages) | Cited 8 times

Online Publication Date: 23 December 2009

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The structural behavior of Cu64.5Zr35.5 bulk metallic glass under compressive stress was investigated by means of in situ high energy x-ray synchrotron diffraction. The topological and chemical short-range order of the glass changes reversible upon loading within the elastic range. The number density of Cu–(Zr,Cu) and Zr–Zr nearest neighbor atomic pairs becomes oriented along the loading direction. The macroscopic stress state is reflected by the medium-range order. The determination of the components of the strain tensor from the shift of the positions of the nearest neighbor distances is not possible due to the structure changes.
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61.43.Dq Amorphous semiconductors, metals, and alloys
64.70.Nd Structural transitions in nanoscale materials
61.46.-w Structure of nanoscale materials

Copolymer solution-based “smart window”

Xiuqing Gong, Jiaxing Li, Shuyu Chen, and Weijia Wen

Appl. Phys. Lett. 95, 251907 (2009); http://dx.doi.org/10.1063/1.3276289 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2009

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The authors report the design of a prototype smart window based on the phenomenon of the thermally induced aggregation of triblock copolymer poly (ethylene oxide)–poly (propylene oxide)–poly (ethylene oxide) (EPE). Fluorescein isothiocyanate was used to label EPE and study aggregation phenomenon at different temperatures. The cloud point could be tuned by mixing EPE with sodium dodecyl sulfate (SDS) and varying the concentration of the latter. The light transmittance at different temperatures was studied as a function of SDS concentration.
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82.35.Jk Copolymers, phase transitions, structure
64.70.Nd Structural transitions in nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
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Characteristics of surface states and charge neutrality level in Ge

Duygu Kuzum, Koen Martens, Tejas Krishnamohan, and Krishna C. Saraswat

Appl. Phys. Lett. 95, 252101 (2009); http://dx.doi.org/10.1063/1.3270529 (3 pages) | Cited 11 times

Online Publication Date: 21 December 2009

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The characteristics of surface states on Ge are investigated using metal/insulator/semiconductor structures and the conductance technique. Evidence of acceptor-like and donor-like surface states on the valence band side of the Ge bandgap is shown by trap time constant analysis. The dependency of trap time constants on trap energy separation from band edge, capture cross section, and temperature are studied through conductance measurements and simulations. The effect of surface states on the location of charge neutrality level at the Ge surface and the consequences such as surface conductivity and negative charge buildup at the interface are discussed.
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73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors
72.80.Cw Elemental semiconductors
68.47.Fg Semiconductor surfaces
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Enhancement of electroluminescence from TiO2/p+-Si heterostructure-based devices through engineering of oxygen vacancies in TiO2

Yuanyuan Zhang, Xiangyang Ma, Peiliang Chen, Dongsheng Li, Xiaodong Pi, Deren Yang, and P. G. Coleman

Appl. Phys. Lett. 95, 252102 (2009); http://dx.doi.org/10.1063/1.3276547 (3 pages) | Cited 3 times

Online Publication Date: 21 December 2009

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We report that electroluminescence (EL) from TiO2/p+-Si heterostructure-based devices can be significantly enhanced through a prior treatment of TiO2 films in argon (Ar) plasma. It is found that the Ar-plasma treatment introduces excess oxygen vacancies within a certain depth of TiO2 films. The increase in the concentration of oxygen vacancies leads to the enhancement of EL from TiO2/p+-Si heterostructure-based devices because oxygen vacancies are the light-emitting centers. This work demonstrates the use of defect engineering to improve the performance of oxide-based optoelectronic devices.
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78.60.Fi Electroluminescence
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.jd Vacancies
61.72.sd Impurity concentration
68.55.ag Semiconductors

Amorphous hafnium-indium-zinc oxide semiconductor thin film transistors

Chang-Jung Kim, Sangwook Kim, Je-Hun Lee, Jin-Seong Park, Sunil Kim, Jaechul Park, Eunha Lee, Jaechul Lee, Youngsoo Park, Joo Han Kim, Sung Tae Shin, and U-In Chung

Appl. Phys. Lett. 95, 252103 (2009); http://dx.doi.org/10.1063/1.3275801 (3 pages) | Cited 65 times

Online Publication Date: 21 December 2009

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We developed amorphous hafnium-indium-zinc oxide (HIZO) thin films as oxide semiconductors and investigated the films electrically and physically. Adding of hafnium (Hf) element can suppress growing the columnar structure and drastically decrease the carrier concentration and hall mobility in HIZO films. The thin film transistors (TFTs) with amorphous HIZO active channel exhibit good electrical properties with field effect mobility of around 10 cm2/Vs, S of 0.23 V/decade, and high Ion/off ratio of over 108, enough to operate the next electronic devices. In particular, under bias-temperature stress test, the HIZO TFTs with 0.3 mol % (Hf content) showed only 0.46 V shift in threshold voltage, compared with 3.25 V shift in HIZO TFT (0.1 mol %). The Hf ions may play a key role to improve the instability of TFTs due to high oxygen bonding ability. Therefore, the amorphous HIZO semiconductor will be a prominent candidate as an operation device for large area electronic applications.
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85.30.Tv Field effect devices
68.55.ag Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
72.20.Ee Mobility edges; hopping transport

Bandgap engineering of graphene: A density functional theory study

Lei Liu and Zexiang Shen

Appl. Phys. Lett. 95, 252104 (2009); http://dx.doi.org/10.1063/1.3276068 (3 pages) | Cited 24 times

Online Publication Date: 21 December 2009

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Three ways of engineering the bandgap of graphene, i.e., surface bonding, isoelectronic codoping, and alternating electrical/chemical environment, are analyzed with the effective mass approximation and density-functional theory calculations. Surface bonding on graphene would lift its top σ valence bands above π valence states, open a sp3 gap, but also bury the linearly dispersive bands into the valence σ bands. Isoelectronic codoping and asymmetric electrical or chemical environment may open the π−π∗ gap of graphene by breaking its sublattice equivalence. The calculated effective mass versus bandgap may provide useful guidance for the future experimental efforts to fabricate graphene-based semiconductors.
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71.20.Tx Fullerenes and related materials; intercalation compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Why nitrogen cannot lead to p-type conductivity in ZnO

J. L. Lyons, A. Janotti, and C. G. Van de Walle

Appl. Phys. Lett. 95, 252105 (2009); http://dx.doi.org/10.1063/1.3274043 (3 pages) | Cited 87 times

Online Publication Date: 22 December 2009

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Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.
Show PACS
72.20.Fr Low-field transport and mobility; piezoresistance
71.15.-m Methods of electronic structure calculations
61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
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