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11 Oct 2010

Volume 97, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 97, 154101 (2010); http://dx.doi.org/10.1063/1.3479052 (3 pages)

Younggeun Park, Yeonho Choi, Debkishore Mitra, Taewook Kang, and Luke P. Lee
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Highly temperature-stable modulation characteristics of multioxide-aperture high-speed 980 nm vertical cavity surface emitting lasers

A. Mutig, J. A. Lott, S. A. Blokhin, P. Wolf, P. Moser, W. Hofmann, A. M. Nadtochiy, A. Payusov, and D. Bimberg

Appl. Phys. Lett. 97, 151101 (2010); http://dx.doi.org/10.1063/1.3499361 (3 pages) | Cited 6 times

Online Publication Date: 11 October 2010

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We present multioxide-aperture 980 nm-range vertical cavity surface emitting lasers (VCSELs) with highly temperature stable modulation characteristics operating error-free at 25 Gbit/s at 25 and 85 °C. We perform small signal modulation experiments and extract the fundamental physical parameters including relaxation resonance frequency, damping factor, parasitic cut-off frequency, D-factor, and K-factor, leading to identification of thermal processes and damping as the main factors that presently limit high speed device operation. We obtain very temperature-insensitive bandwidths around 13–15 GHz. Presented results clearly demonstrate the suitability of our VCSELs for practical and reliable optical data transmission systems.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Effect of periodicity on optical forces between a one-dimensional periodic photonic crystal waveguide and an underlying substrate

Jing Ma and Michelle L. Povinelli

Appl. Phys. Lett. 97, 151102 (2010); http://dx.doi.org/10.1063/1.3493658 (3 pages) | Cited 8 times

Online Publication Date: 11 October 2010

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We numerically investigate the attractive optical force between a suspended one-dimensional periodic photonic crystal waveguide and underlying substrate in a silicon-on-insulator platform. We show that the optical force is enhanced by designing the waveguide cross section to make the mode approach the band edge or substrate light line. We show that for periodic waveguides, the optical force is nonmonotonic with waveguide-substrate separation. This effect may enable the design of compact, integrated optical power limiters.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Room-temperature photoresponse of Schottky photodiodes based on GaNxAs1−x synthesized by ion implantation and pulsed-laser melting

Wei Yi, Taeseok Kim, Ilan Shalish, Marko Loncar, Michael J. Aziz, and Venkatesh Narayanamurti

Appl. Phys. Lett. 97, 151103 (2010); http://dx.doi.org/10.1063/1.3500981 (3 pages) | Cited 1 time

Online Publication Date: 11 October 2010

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The spectral responsivity for Schottky photodiodes based on the GaNxAs1−x alloys synthesized using nitrogen (N) ion implantation followed by pulsed-laser melting and rapid thermal annealing is presented. An N-induced redshift up to 250 meV (180 nm) in the photocurrent onset energy (wavelength) is observed. The N concentration dependence agrees with the values measured by photomodulated reflectance and ballistic electron emission microscopy, and with the calculation by the band anticrossing model for the splitting of the conduction band in GaNxAs1−x.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes

Continuously tunable monomode mid-infrared vertical external cavity surface emitting laser on Si

A. Khiar, M. Rahim, M. Fill, F. Felder, F. Hobrecker, and H. Zogg

Appl. Phys. Lett. 97, 151104 (2010); http://dx.doi.org/10.1063/1.3501134 (3 pages) | Cited 9 times

Online Publication Date: 11 October 2010

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A tunable PbTe based mid-infrared vertical external cavity surface emitting laser is described. The active part is a ∼ 1 μm thick PbTe layer grown epitaxially on a Bragg mirror on the Si-substrate. The cavity is terminated with a curved Si/SiO Bragg top mirror and pumped optically with a 1.55 μm laser. Cavity length is <100 μm in order that only one longitudinal mode is supported. By changing the cavity length, up to 5% wavelength continuous and mode-hop free tuning is achieved at fixed temperature. The total tuning extends from 5.6 to 4.7 μm at 100–170 K operation temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Photonic crystal slot nanobeam slow light waveguides for refractive index sensing

Bowen Wang, Mehmet A. Dündar, Richard Nötzel, Fouad Karouta, Sailing He, and Rob W. van der Heijden

Appl. Phys. Lett. 97, 151105 (2010); http://dx.doi.org/10.1063/1.3497296 (3 pages) | Cited 14 times

Online Publication Date: 11 October 2010

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We present the design, fabrication, and photoluminescence experiment of InGaAsP photonic crystal slot nanobeam slow light waveguides with embedded InAs quantum dots. The strong confinement of electric field in the slot region is confirmed by the measured record high sensitivity of 7×102 nm per refractive index unit (RIU) to the refractive index change of the environment. A cavity, formed by locally deflecting the two beams toward each other, gives an even higher sensitivity of about 9×102 nm/RIU.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.15.Eq Optical system design

Carrier localization in m-plane InGaN/GaN quantum wells probed by scanning near field optical spectroscopy

V. Liuolia, A. Pinos, S. Marcinkevičius, Y. D. Lin, H. Ohta, S. P. DenBaars, and S. Nakamura

Appl. Phys. Lett. 97, 151106 (2010); http://dx.doi.org/10.1063/1.3502482 (3 pages) | Cited 7 times

Online Publication Date: 12 October 2010

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Scanning near field optical microscopy (SNOM) was applied to study the carrier localization in single InGaN/GaN quantum well structures grown on nonpolar m-plane GaN substrates. Dual localization potential consisting of hundreds of nanometers- to micrometer-size areas as well as smaller localization centers were identified from the SNOM scans and near field photoluminescence spectral widths. The localization areas were found to align along the [0001] direction, which was attributed to partial strain relaxation at the monolayer steps.
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78.67.De Quantum wells
81.07.St Quantum wells
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Cerenkov radiation in metallic metamaterials

Jin-Kyu So, Jong-Hyo Won, M. A. Sattorov, Seung-Ho Bak, Kyu-Ha Jang, Gun-Sik Park, D. S. Kim, and F. J. Garcia-Vidal

Appl. Phys. Lett. 97, 151107 (2010); http://dx.doi.org/10.1063/1.3492846 (3 pages) | Cited 3 times

Online Publication Date: 12 October 2010

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The electromagnetic response of a metallic metamaterial to fast-moving electrons is studied by numerical simulations. The considered metamaterial is a one-dimensional array of slits perforated on a metallic film and is found to generate Cerenkov wakes when the electron beam travels near its surface. There is no energy threshold for the generation of such wakes, which would be promising to lower the operation energy of the electron beam in compact Cerenkov free-electron-lasers. Moreover, by analyzing the spectral dependence of the Cerenkov light, it is possible to map the dispersion relation of the guided modes supported by the metamaterial.
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61.80.Fe Electron and positron radiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
41.60.Bq Cherenkov radiation
42.70.Hj Laser materials

Nanowire superconducting single-photon detectors on GaAs for integrated quantum photonic applications

A. Gaggero, S. Jahanmiri Nejad, F. Marsili, F. Mattioli, R. Leoni, D. Bitauld, D. Sahin, G. J. Hamhuis, R. Nötzel, R. Sanjines, and A. Fiore

Appl. Phys. Lett. 97, 151108 (2010); http://dx.doi.org/10.1063/1.3496457 (3 pages) | Cited 11 times

Online Publication Date: 12 October 2010

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We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350 °C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at λ = 1300 nm and T = 4.2 K.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Random laser action in GaN nanocolumns

Masaru Sakai, Yuta Inose, Kazuhiro Ema, Tomi Ohtsuki, Hiroto Sekiguchi, Akihiko Kikuchi, and Katsumi Kishino

Appl. Phys. Lett. 97, 151109 (2010); http://dx.doi.org/10.1063/1.3495993 (3 pages) | Cited 9 times

Online Publication Date: 13 October 2010

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We report observations of random laser action in self-organized GaN nanocolumns. We have measured three samples with different filling fractions and investigated the dependence of the lasing property on the random configuration of nanocolumns. Numerical calculations based on a finite-difference time-domain method have also been performed and the comparison with the experimental results shows a clear relationship between the strength of light localization and the occurrence of random laser action.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer

H. B. Dang, A. C. Maloof, and M. V. Romalis

Appl. Phys. Lett. 97, 151110 (2010); http://dx.doi.org/10.1063/1.3491215 (3 pages) | Cited 21 times

Online Publication Date: 14 October 2010

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We describe an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin-exchange relaxation free regime. We demonstrate magnetic field sensitivity of 160 aT/Hz1/2 in a gradiometer arrangement with a measurement volume of 0.45 cm3 and energy resolution per unit bandwidth of 44ℏ. As an example of an application enabled by such a magnetometer, we describe measurements of weak remnant rock magnetization as a function of temperature with a sensitivity on the order of 10−10 emu/cm3/Hz1/2 and temperatures up to 420°C.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
91.60.Pn Magnetic and electrical properties
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Design and optimization of a high-efficiency nanoscale ±90° light-bending structure by mode selection and tailoring

M. W. Maqsood, R. Mehfuz, and K. J. Chau

Appl. Phys. Lett. 97, 151111 (2010); http://dx.doi.org/10.1063/1.3501130 (3 pages)

Online Publication Date: 14 October 2010

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We tailor the dispersive properties of a nanoscale structure to enable ±90° visible light-bending. The geometry and constituent materials of the structure are selected such that two low-loss modes are available to channel light toward and away from a nanoscale 90°-bend. Based on numerical simulations of visible light propagation through the structure, we propose an optimized geometry that yields maximum field overlap between the mode propagating toward and the mode propagating away from the 90°-bend, resulting in a peak bending efficiency of 92%.
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42.79.Gn Optical waveguides and couplers
42.25.Bs Wave propagation, transmission and absorption

Poling-inhibited ridge waveguides in lithium niobate crystals

C. L. Sones, P. Ganguly, C. Y. J. Ying, E. Soergel, R. W. Eason, and S. Mailis

Appl. Phys. Lett. 97, 151112 (2010); http://dx.doi.org/10.1063/1.3504698 (3 pages) | Cited 3 times

Online Publication Date: 15 October 2010

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Ultraviolet laser irradiation of a lithium niobate +z polar surface enables the production of ridge waveguides. Ultraviolet laser induced inhibition of poling is used to define an inverted domain pattern which transforms into a ridge structure by differential etching in hydrofluoric acid. The laser irradiation step also induces a refractive index change that provides the vertical confinement within the ridge structure. Furthermore, it was observed that poling-inhibition results in a significant enhancement of the refractive index contrast between the bulk crystal and the ultraviolet irradiated tracks.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.60.-v Laser optical systems: design and operation

Silicon-photonics light source realized by III–V/Si-grating-mirror laser

Il-Sug Chung and Jesper Mørk

Appl. Phys. Lett. 97, 151113 (2010); http://dx.doi.org/10.1063/1.3503966 (3 pages) | Cited 5 times

Online Publication Date: 15 October 2010

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A III–V/Si vertical-cavity in-plane-emitting laser structure is suggested and numerically investigated. This hybrid laser consists of a distributed Bragg reflector, a III–V active region, and a high-index-contrast grating (HCG) connected to an in-plane output waveguide. The HCG and the output waveguide are made in the Si layer of a silicon-on-insulator wafer by using Si-electronics-compatible processing. The HCG works as a highly-reflective mirror for vertical resonance and at the same time routes light to the in-plane output waveguide. Numerical simulations show superior performance compared to existing silicon light sources.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.82.Et Waveguides, couplers, and arrays
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
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Gas flow dependence of ground state atomic oxygen in plasma needle discharge at atmospheric pressure

Yukinori Sakiyama, Nikolas Knake, Daniel Schröder, Jörg Winter, Volker Schulz-von der Gathen, and David B. Graves

Appl. Phys. Lett. 97, 151501 (2010); http://dx.doi.org/10.1063/1.3496041 (3 pages) | Cited 3 times

Online Publication Date: 11 October 2010

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We present clear evidence that ground state atomic oxygen shows two patterns near a surface in the helium plasma needle discharge. Two-photon absorption laser-induced fluorescence spectroscopy, combined with gas flow simulation, was employed to obtain spatially-resolved ground state atomic oxygen densities. When the feed gas flow rate is low, the radial density peaks along the axis of the needle. At high flow rate, a ring-shaped density distribution appears. The peak density is on the order of 1021 m−3 in both cases. The results are consistent with a previous report of the flow-dependent bacterial killing pattern observed under similar conditions.
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52.30.-q Plasma dynamics and flow
52.25.-b Plasma properties
52.80.Tn Other gas discharges
52.65.-y Plasma simulation

An analytical formulation for the modified Paschen’s curve

Rakshit Tirumala and David B. Go

Appl. Phys. Lett. 97, 151502 (2010); http://dx.doi.org/10.1063/1.3497231 (3 pages) | Cited 15 times

Online Publication Date: 11 October 2010

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The modified Paschen’s curve describes the gaseous breakdown potential (voltage) in microscale gaps, when deviations from the traditional Paschen’s curve occur [ F. Paschen, Ann. Phys. 273, 69 (1889) ]. The deviation is due to ion-enhanced field emission that occurs in the high electric field of microgaps and acts as an additional cathode electron source. The present work derives an analytical formulation for the effect of ion-enhanced field emission and the modified Paschen’s curve that uses a consistent, single breakdown criterion. The proposed model does not require the fitting factor required in prior models and constitutes a single analytical equation for microscale breakdown and the modified Paschen’s curve.
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51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption

Plasma-enabled growth of separated, vertically aligned copper-capped carbon nanocones on silicon

S. Kumar, I. Levchenko, M. Keidar, and K. Ostrikov

Appl. Phys. Lett. 97, 151503 (2010); http://dx.doi.org/10.1063/1.3502562 (3 pages) | Cited 9 times

Online Publication Date: 13 October 2010

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The formation of vertically aligned, clearly separated, copper-capped carbon nanocones with a length of up to 500 nm and base diameter of about 150 nm via three-stage process involving magnetron sputtering, N2 plasma treatment, and CH4+N2 plasma growth is studied. The width of gaps between the nanocones can be controlled by the gas composition. The nanocone formation mechanism is explained in terms of strong passivation of carbon in narrow gaps, where the access of plasma ions is hindered and the formation of large CnH2n+2 molecules is possible. This plasma-enabled approach can be used to fabricate nanoelectronic, nanofluidic, and optoelectronic components and devices.
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81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
81.65.Rv Passivation
61.46.-w Structure of nanoscale materials
52.77.Dq Plasma-based ion implantation and deposition
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Phase stability and decomposition products of Ti–Al–Ta–N thin films

R. Rachbauer, D. Holec, and P. H. Mayrhofer

Appl. Phys. Lett. 97, 151901 (2010); http://dx.doi.org/10.1063/1.3495783 (3 pages) | Cited 10 times

Online Publication Date: 11 October 2010

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Ab initio calculations of quaternary alloys were used to predict the phase stability of (Ti1−xAlx)1−yTayN. Experimental observation of a dual phase structure containing wurtzite AlN and cubic Ti1−yTayN after thermal decomposition of sputter deposited thin films by vacuum annealing to 1400 °C is in excellent agreement with the calculated phase stabilities of the investigated compositions. We found positive mixing enthalpies for Ti1−xAlxN and Al1−yTayN, with maximum values of 0.25 eV/atom and 0.30 eV/atom, respectively, but negative values for Ti1−yTayN over the whole composition range. The difference in lattice parameters obtained from experiments and ab initio calculations is within ∼ 1%.
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68.60.Dv Thermal stability; thermal effects
81.40.Gh Other heat and thermomechanical treatments
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
64.75.Ef Mixing
61.66.Fn Inorganic compounds

High oxidation state at the epitaxial interface of γ-Al2O3 thin films grown on Si(111) and Si(001)

M. El Kazzi, C. Merckling, G. Saint-Girons, G. Grenet, M. Silly, F. Sirotti, and G. Hollinger

Appl. Phys. Lett. 97, 151902 (2010); http://dx.doi.org/10.1063/1.3499280 (3 pages) | Cited 1 time

Online Publication Date: 11 October 2010

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High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial γ-Al2O3 and Si substrate. The experiments were performed on 1 nm thick epitaxial γ-Al2O3 layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si2+ and Si3+ species and the presence of two different Si4+ species. A microscopic model is proposed for the interface obtained with two incomplete SiO2 planes based on the Si 2p3/2 line shape.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.aj Insulators
61.50.Lt Crystal binding; cohesive energy

Coupled thermomechanics of single-wall carbon nanotubes

F. Scarpa, L. Boldrin, H. X. Peng, C. D. L. Remillat, and S. Adhikari

Appl. Phys. Lett. 97, 151903 (2010); http://dx.doi.org/10.1063/1.3499748 (3 pages) | Cited 6 times

Online Publication Date: 11 October 2010

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The temperature-dependent transverse mechanical properties of single-walled nanotubes are studied using a molecular mechanics approach. The stretching and bond angle force constants describing the mechanical behavior of the sp2 bonds are resolved in the temperature range between 0 and 1600 K, allowing to identify a temperature dependence of the nanotubes wall thickness. We observe a decrease of the stiffness properties (axial and shear Young’s modulus) with increasing temperatures, and an augmentation of the transverse Poisson’s ratio, with magnitudes depending on the chirality of the nanotube. Our closed-form predictions compare well with existing molecular dynamics simulations.
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62.20.dj Poisson's ratio
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.dq Other elastic constants
81.40.Gh Other heat and thermomechanical treatments

A shear thickening phenomenon in magnetic field controlled-dipolar suspensions

Yu Tian, Jile Jiang, Yonggang Meng, and Shizhu Wen

Appl. Phys. Lett. 97, 151904 (2010); http://dx.doi.org/10.1063/1.3501128 (3 pages) | Cited 10 times

Online Publication Date: 11 October 2010

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A shear thickening phenomenon in dipolar suspensions of magnetorheological (MR) fluid is reported. The stress of the MR fluid abruptly decreases when the applied magnetic field increases to above a critical value under a small constant shear rate. It abruptly increases when the shear rate is higher than a critical value under a constant magnetic field, accompanied by a change in normal stress during shear thickening or unshear thickening processes. A shear-thickened structure is important for an MR fluid to obtain a high yield stress, which is beyond the prediction of a traditional dipole or multipole interaction model.
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82.70.Kj Emulsions and suspensions
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
47.65.Cb Magnetic fluids and ferrofluids
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Si(100) surfaces in a hydrogen-based process ambient

Henning Döscher, Anja Dobrich, Sebastian Brückner, Peter Kleinschmidt, and Thomas Hannappel

Appl. Phys. Lett. 97, 151905 (2010); http://dx.doi.org/10.1063/1.3497992 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2010

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We studied the atomic surface properties of Si(100) during preparation in a (metal-organic) vapor phase epitaxy (VPE) reactor and the impact of the hydrogen ambient. Absorption lines in Fourier-transform infrared spectra were identified as stretch modes of coupled Si–H monohydrides, in agreement with Si-dimers observed by scanning tunneling microscopy. The polarization dependence of the antisymmetric stretch mode distinguished different dimer orientations and verified a clear preference for one of the (2×1)/(1×2) surface reconstruction domains. Tip-induced H-desorption proved the complete saturation of dangling bonds after VPE-preparation. In situ reflectance anisotropy spectroscopy showed the absence of Si–H bonds at elevated annealing temperature.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators

Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft x-ray reflectivity study

Sarab Preet Singh, Mohammed H. Modi, and P. Srivastava

Appl. Phys. Lett. 97, 151906 (2010); http://dx.doi.org/10.1063/1.3497284 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2010

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We report soft x-ray reflectivity measurements near the Si L2,3 absorption edge for Si-rich silicon nitride thin film obtained by Hg-sensitized photochemical vapor deposition. We demonstrate that the precise analysis of optical index profile derived over extended energy region gives compositional details of the film. This nondestructive approach is used in Si-rich silicon nitride film to reveal buried Si-rich interfacial layer. Further, the combined study of soft x-ray reflectivity and optical density obtained from the reflectivity fitting at various photon energies provide a qualitative estimation of the film composition and its growth.
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68.55.aj Insulators
68.55.Nq Composition and phase identification
82.50.-m Photochemistry
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

An empirical potential for silicon under conditions of strong electronic excitation

Lalit Shokeen and Patrick K. Schelling

Appl. Phys. Lett. 97, 151907 (2010); http://dx.doi.org/10.1063/1.3499296 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2010

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We present an empirical potential developed for silicon under conditions of strong electronic excitation. We show the essentially athermal nature of the melting transition when the electronic temperature is extremely high. The resulting liquid is shown to be distinct from ordinary liquid silicon. For less intense excitations, we determine the thermal melting temperature and demonstrate the possible existence of a regime where ordinary thermodynamic melting can occur but at a reduced temperature Tm. We show laser-induced softening of the lattice can lead to lattice cooling for very short time scales ( ∼ 100 fs), an effect never before recognized.
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64.70.dj Melting of specific substances
71.22.+i Electronic structure of liquid metals and semiconductors and their alloys
81.05.Cy Elemental semiconductors

Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy

X. Q. Wang, H. P. Sun, and X. Q. Pan

Appl. Phys. Lett. 97, 151908 (2010); http://dx.doi.org/10.1063/1.3502607 (3 pages) | Cited 3 times

Online Publication Date: 13 October 2010

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Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.35.Ct Interface structure and roughness
68.37.Og High-resolution transmission electron microscopy (HRTEM)
81.05.Dz II-VI semiconductors

Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

X. J. Chen, G. Perillat-Merceroz, D. Sam-Giao, C. Durand, and J. Eymery

Appl. Phys. Lett. 97, 151909 (2010); http://dx.doi.org/10.1063/1.3497078 (3 pages) | Cited 15 times

Online Publication Date: 13 October 2010

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The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([000math]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff’s plot points out the effect of surface polarity.
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81.07.Gf Nanowires
81.07.Vb Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.67.Uh Nanowires
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