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12 Mar 2012

Volume 100, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages)

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz
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Quantitative absorption spectra of quantum wires measured by analysis of attenuated internal emissions

Masahiro Yoshita, Takayuki Okada, Hidefumi Akiyama, Makoto Okano, Toshiyuki Ihara, Loren N. Pfeiffer, and Ken W. West

Appl. Phys. Lett. 100, 112101 (2012); http://dx.doi.org/10.1063/1.3693401 (4 pages) | Cited 1 time

Online Publication Date: 12 March 2012

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An absorption-spectroscopy method that utilizes internal emissions as the source of the probe light was used to measure the absorption spectra of quasi-one-dimensional (q-1D) excitons in T-shaped quantum wires embedded in an optical waveguide. The modal absorption area of the 1D ground-state excitons was estimated to be 0.39 eV cm−1 and was almost independent of temperature in the range 4–150 K. Quantitative evaluation using the absorption spectra revealed that the absorption cross-section per unit length at resonance peak and the spectrally integrated absorption cross-section area per unit length of the 1D ground-state excitons were 1.0 nm and 2.5 × 10−3 eV nm, respectively.
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78.67.Lt Quantum wires
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.55.-m Photoluminescence, properties and materials
73.22.Lp Collective excitations
71.35.-y Excitons and related phenomena

Physical understanding of cryogenic implant benefits for electrical junction stability

Fareen Adeni Khaja, Benjamin Colombeau, Thirumal Thanigaivelan, Deepak Ramappa, and Todd Henry

Appl. Phys. Lett. 100, 112102 (2012); http://dx.doi.org/10.1063/1.3694275 (4 pages)

Online Publication Date: 13 March 2012

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We investigate the effect of cryogenic temperature implants on electrical junction stability for ultra shallow junction applications for sub-32 nm technology nodes and beyond. A comprehensive study was conducted to gain physical understanding of the impact of cryogenic temperature implants on dopant-defect interactions. Carborane (C2B10H12) molecule, a potential alternative to monomer boron was implanted in carbon preamorphized silicon substrates at cryogenic implant temperatures. Results indicate implants at cryogenic temperatures increase dopant activation with reduced diffusion, resulting in lower sheet resistance for a lower junction depth. Further, this study emphasizes the benefits of co-implants performed at cryogenic temperatures as alternative to traditional preamorphizing implants.
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61.72.up Other materials
61.72.U- Doping and impurity implantation
85.40.Ry Impurity doping, diffusion and ion implantation technology
66.30.Ny Chemical interdiffusion; diffusion barriers
61.80.-x Physical radiation effects, radiation damage

Metal enhanced photoluminescence from Al-capped ZnMgO films: The roles of plasmonic coupling and non-radiative recombination

Yanjie Wang, Haiping He, Yalin Zhang, Luwei Sun, Liang Hu, Kewei Wu, Jingyun Huang, and Zhizhen Ye

Appl. Phys. Lett. 100, 112103 (2012); http://dx.doi.org/10.1063/1.3693396 (4 pages) | Cited 5 times

Online Publication Date: 13 March 2012

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Aluminium (Al) enhanced emission is investigated by temperature-dependent photoluminescence (PL) from ZnMgO films grown by metal-organic chemical vapor deposition. The PL enhancement is sensitive to both the thickness of Al film and the temperature. The enhancement ratio increases from 3.5 to ∼51 when temperature decreases from room temperature to 20 K. Increased surface plasmon (SP) coupling and decreased non-radiative recombination rate with decreasing temperature are suggested to account for the giant enhancement. The coupling between the ZnMgO excitons and the SP resonance is confirmed by time-resolved PL.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Dz II-VI semiconductors
68.55.ag Semiconductors

Simulation study of channel mobility and device performance dependence on gate stack in graphene field-effect transistors

Weinan Zhu, Jinyu Zhang, and Zhiping Yu

Appl. Phys. Lett. 100, 112104 (2012); http://dx.doi.org/10.1063/1.3693410 (5 pages) | Cited 1 time

Online Publication Date: 13 March 2012

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The channel mobility and device performance of graphene field-effect transistors (GFETs) were investigated using a theoretical model. Surface polarized phonon scattering and charged impurity Coulomb scattering are two dominant scattering mechanisms in carrier mobility calculation. Mobilities are used to calculate the drain current and transconductance of GFETs. Adding a polymer buffer layer (PBL) with low permittivity between graphene and gate dielectric can effectively improve GFETs performance at the expense of decreasing gate controllability. PBL thickness was optimized to achieve best device transconductance. Experimental results and the model calculations of both channel mobility and device transconductance are in agreement.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
73.61.Wp Fullerenes and related materials
72.20.Fr Low-field transport and mobility; piezoresistance

High-performance uncooled distributed-feedback quantum cascade laser without lateral regrowth

J. C. Zhang, F. Q. Liu, S. Tan, D. Y. Yao, L. J. Wang, L. Li, J. Q. Liu, and Z. G. Wang

Appl. Phys. Lett. 100, 112105 (2012); http://dx.doi.org/10.1063/1.3693425 (4 pages) | Cited 3 times

Online Publication Date: 13 March 2012

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We demonstrate, uncooled, room-temperature continuous-wave (cw) operation of single-mode distributed-feedback (DFB) quantum cascade lasers (QCLs) emitting around 4.6 μm without lateral regrowth. The effects of cavity length on device performance are studied. A record low threshold electrical power consumption of 2.3 W for the entire laser system with a 1.5-mm-long cavity is realized. For the 2-mm-long laser, high cw output power of 125 mW and very low threshold current density of 0.86 kA/cm2 are obtained. Our devices represent an important step towards using uncooled DFB QCLs in mid-infrared spectral range for practical applications.
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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

Optical investigation of degradation mechanisms in AlGaN/GaN high electron mobility transistors: Generation of non-radiative recombination centers

C. Hodges, N. Killat, S. W. Kaun, M. H. Wong, F. Gao, T. Palacios, U. K. Mishra, J. S. Speck, D. Wolverson, and M. Kuball

Appl. Phys. Lett. 100, 112106 (2012); http://dx.doi.org/10.1063/1.3693427 (4 pages) | Cited 2 times

Online Publication Date: 13 March 2012

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Degradation mechanisms in AlGaN/GaN high electron mobility transistors have been studied under pinch-off conditions. Sites of localized emission of electroluminescence (EL) in the form of hotspots, known to be related to gate leakage currents, are shown to be the result of the generation of non-radiative recombination centers in the AlGaN device layer during device stress. EL from the hotspot site contains both hot-carrier emission from the acceleration of charge carriers in the device channel and defect-related transitions. Gate leakage through the generated centers is the most likely mechanism for the observation of EL hotspots.
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85.30.Tv Field effect devices

Scanning tunneling microscopy reveals LiMnAs is a room temperature anti-ferromagnetic semiconductor

A. P. Wijnheijmer, X. Martí, V. Holý, M. Cukr, V. Novák, T. Jungwirth, and P. M. Koenraad

Appl. Phys. Lett. 100, 112107 (2012); http://dx.doi.org/10.1063/1.3693611 (4 pages)

Online Publication Date: 14 March 2012

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We performed scanning tunneling microscopy and spectroscopy on a LiMnAs(001) thin film epitaxially grown on an InAs(001) substrate by molecular beam epitaxy. While the in situ cleavage exposed only the InAs(110) non-polar planes, the cleavage continued into the LiMnAs thin layer across several facets. We combined both topography and current mappings to confirm that the facets correspond to LiMnAs. By spectroscopy we show that LiMnAs has a band gap. The band gap evidenced in this study, combined with the known Néel temperature well above room temperature, confirms that LiMnAs is a promising candidate for exploring the concepts of high temperature semiconductor spintronics based on antiferromagnets.
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68.35.bg Semiconductors
68.55.ag Semiconductors
75.50.Ee Antiferromagnetics
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Evolution of deep electronic states in ZnO during heat treatment in oxygen- and zinc-rich ambients

V. Quemener, L. Vines, E. V. Monakhov, and B. G. Svensson

Appl. Phys. Lett. 100, 112108 (2012); http://dx.doi.org/10.1063/1.3693612 (4 pages) | Cited 4 times

Online Publication Date: 14 March 2012

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Hydrothermally grown ZnO samples have been annealed in Ar, Zn-rich, and O-rich ambients and investigated by deep level transient spectroscopy (DLTS). The DLTS measurements reveal up to 6 different defect levels in the band gap after different annealing conditions. A clear correlation has been found between the annealing treatment and the formation/suppression of two deep defect levels at ∼0.2 and ∼0.5 eV below the conduction band edge (Ec). As a result, the Ec-0.5eV level is assigned to a Zn-rich defect while the Ec-0.2eV level is due to a O-rich defect, where the latter shows donor behavior as revealed by a distinct Poole-Frenkel effect.
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71.55.Gs II-VI semiconductors
72.20.Ht High-field and nonlinear effects
81.40.Gh Other heat and thermomechanical treatments
71.20.Nr Semiconductor compounds

Electrical characterization of a-InGaZnO thin-film transistors with Cu source/drain electrodes

Jaewook Jeong, Gwang Jun Lee, Joonwoo Kim, and Byeongdae Choi

Appl. Phys. Lett. 100, 112109 (2012); http://dx.doi.org/10.1063/1.3694273 (4 pages) | Cited 2 times

Online Publication Date: 15 March 2012

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We analyzed the effects of Cu source/drain (S/D) electrodes on the performance of a-InGaZnO (a-IGZO) thin-film transistors (TFTs). Owing to the Cu migration, the parasitic resistance was as low as 10 Ω cm with small current transfer length. Based on the transfer characteristics, we found that VDS dependent Cu migration creates donor-like deep and tail states in the sub-bandgap region. The feasibility of Cu S/D electrodes for a-IGZO TFTs using inverter circuits indicates that fabrication of high performance circuits is possible by controlling the Cu electro-migration.
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85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation
84.30.Jc Power electronics; power supply circuits

Effects of molecular beam epitaxy growth conditions on composition and optical properties of InxGa1−xBiyAs1−y

Y. Zhong, P. B. Dongmo, J. P. Petropoulos, and J. M. O. Zide

Appl. Phys. Lett. 100, 112110 (2012); http://dx.doi.org/10.1063/1.3695066 (4 pages) | Cited 4 times

Online Publication Date: 16 March 2012

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We describe the growth conditions of InxGa1−xBiyAs1−y (lattice-mismatched and matched) on InP substrates by molecular beam epitaxy and the resulting properties. Due to their anomalously narrow bandgaps and the presence of bismuth, these materials are promising for optoelectronics and thermoelectrics. Low growth temperature and moderate As/Bi beam equivalent pressure ratios are beneficial for Bi incorporation, in good qualitative agreement with GaBiyAs1−y on GaAs. Up to 6.75% bismuth is incorporated. High resolution x-ray diffraction and reciprocal space mapping show that InxGa1−xBiyAs1−y samples exhibit good crystalline quality and zero relaxation. The band gap is reduced in agreement with theoretical predictions. Lattice-matched samples have been produced with lattice mismatch ≤0.21%.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Large magnetothermopower effect in Dirac materials (Sr/Ca)MnBi2

Kefeng Wang, Limin Wang, and C. Petrovic

Appl. Phys. Lett. 100, 112111 (2012); http://dx.doi.org/10.1063/1.3695155 (3 pages) | Cited 1 time

Online Publication Date: 16 March 2012

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We report temperature and magnetic field dependence of the thermal transport properties in single crystals of (Sr/Ca)MnBi2 with linear energy dispersion. In SrMnBi2 thermopower is positive, indicating hole-type carriers and the magnetic field enhances the thermopower significantly. The maximum change of thermopower is about 1600% in 9 T field and at 10 K. A negative thermopower is observed in CaMnBi2 with dominant electron-type carriers, and, in contrast, the magnetic field suppresses the absolute value of thermopower. First-principle band structure shows that the chemical potential is close to the Dirac-cone-like points in linear bands. The magnetic field suppresses the apparent Hall carrier density of CaMnBi2 below 50 K. The large magnetothermopower effect in (Sr/Ca)MnBi2 is attributed to the magnetic field shift of chemical potential.
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72.15.Jf Thermoelectric and thermomagnetic effects
71.15.-m Methods of electronic structure calculations
72.15.Gd Galvanomagnetic and other magnetotransport effects
65.40.G- Other thermodynamical quantities
71.20.Lp Intermetallic compounds

Controlling dopant profiles in hyperdoped silicon by modifying dopant evaporation rates during pulsed laser melting

Daniel Recht, Joseph T. Sullivan, Robert Reedy, Tonio Buonassisi, and Michael J. Aziz

Appl. Phys. Lett. 100, 112112 (2012); http://dx.doi.org/10.1063/1.3695171 (3 pages) | Cited 2 times

Online Publication Date: 16 March 2012

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We describe a method to control the sub-surface dopant profile in “hyperdoped” silicon fabricated by ion implantation and pulsed laser melting. Dipping silicon ion implanted with sulfur into hydrofluoric acid prior to nanosecond pulsed laser melting leads to a tenfold increase in the rate of sulfur evaporation from the surface of the melt. This results in an 80% reduction of the near-surface dopant concentration, effectively embedding the hyperdoped region in a layer up to 180 nm beneath the surface. This method should facilitate the development of blocked impurity band devices.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
64.70.dj Melting of specific substances
68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors

A nitrogen-related deep level defect in ion implanted 4H-SiC pn junctions—A spin dependent recombination study

Thomas Aichinger, Patrick M. Lenahan, Blair R. Tuttle, and Dethard Peters

Appl. Phys. Lett. 100, 112113 (2012); http://dx.doi.org/10.1063/1.3695330 (4 pages) | Cited 1 time

Online Publication Date: 16 March 2012

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Nitrogen implantation creates a high density of recombination centers in SiC which can degrade the performance of ion implanted pn junctions. We use spin dependent recombination (SDR) to identify deep level defects associated with these centers. We find a dominating SDR spectrum with three strong lines of equal intensity. The SDR pattern indicates that the observed center is a defect complex involving nitrogen.
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71.55.Ht Other nonmetals
61.72.up Other materials
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