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14 Sep 2009

Volume 95, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 95, 113101 (2009); http://dx.doi.org/10.1063/1.3197646 (3 pages)

Jesse J. Cole, En-Chiang Lin, Chad R. Barry, and Heiko O. Jacobs
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E centers in ternary Si1−x−yGexSny random alloys

A. Chroneos, C. Jiang, R. W. Grimes, U. Schwingenschlögl, and H. Bracht

Appl. Phys. Lett. 95, 112101 (2009); http://dx.doi.org/10.1063/1.3224894 (3 pages) | Cited 21 times

Online Publication Date: 14 September 2009

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Density functional theory calculations are used to study the association of arsenic (As) atoms to lattice vacancies and the formation of As-vacancy pairs, known as E centers, in the random Si0.375Ge0.5Sn0.125 alloy. The local environments are described by 32-atom special quasirandom structures that represent random Si1−x−yGexSny alloys. It is predicted that the nearest-neighbor environment will exert a strong influence on the stability of E centers in ternary Si0.375Ge0.5Sn0.125.
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61.72.jn Color centers
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Bandgap and band offsets determination of semiconductor heterostructures using three-terminal ballistic carrier spectroscopy

Wei Yi, Venkatesh Narayanamurti, Hong Lu, Michael A. Scarpulla, Arthur C. Gossard, Yong Huang, Jae-Hyun Ryou, and Russell D. Dupuis

Appl. Phys. Lett. 95, 112102 (2009); http://dx.doi.org/10.1063/1.3224914 (3 pages) | Cited 2 times

Online Publication Date: 14 September 2009

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Utilizing ambipolar tunnel emission of ballistic electrons and holes, we have developed a model-independent method to self-consistently measure bandgaps of semiconductors and band offsets at semiconductor heterojunctions. Lattice-matched GaAs/AlxGa1−xAs and GaAs/(AlxGa1−x)0.51In0.49P (100) single-barrier heterostructures are studied at 4.2 K. For the GaAs/AlGaAs interface, the measured Γ band offset ratio is 60.4:39.6 (±2%). For the heteroanion GaAs/AlGaInP (100) interface, this ratio varies with the Al composition and is distributed more in the valence band. The indirect-gap X band offsets observed at the GaAs/AlGaInP interface deviates from predictions by the transitivity rule.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.80.Ey III-V and II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Nr Semiconductor compounds
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport

Photoluminescence-based measurements of the energy gap and diffusion length of Zn3P2

Gregory M. Kimball, Astrid M. Müller, Nathan S. Lewis, and Harry A. Atwater

Appl. Phys. Lett. 95, 112103 (2009); http://dx.doi.org/10.1063/1.3225151 (3 pages) | Cited 6 times

Online Publication Date: 14 September 2009

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The steady-state photoluminescence spectra of zinc phosphide (Zn3P2) wafers have revealed a fundamental indirect band gap at 1.38 eV, in close proximity to the direct band gap at 1.50 eV. These values are consistent with the values for the indirect and direct band gaps obtained from analysis of the complex dielectric function deduced from spectroscopic ellipsometric measurements. Bulk minority carrier lifetimes of 20 ns were observed by time-resolved photoluminescence decay measurements, implying minority-carrier diffusion lengths of ≥ 7 μm.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.jd Time resolved luminescence
72.80.Jc Other crystalline inorganic semiconductors

Electrical behavior of electrospun heterostructured Ag–ZnO nanofibers

Dandan Lin, Hui Wu, Xiaolu Qin, and Wei Pan

Appl. Phys. Lett. 95, 112104 (2009); http://dx.doi.org/10.1063/1.3227691 (3 pages) | Cited 2 times

Online Publication Date: 15 September 2009

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In this work, the electrical behavior of heterostructured Ag–ZnO nanofibers was studied by varying the Ag content. The electric conductivity of the hybrids follows the percolation theory and can reach as high as 115 S cm−1 due to the electron transfer highway provided by Ag phase. Typical low-voltage varistor behavior, with nonlinear coefficient of ∼ 10, was observed for samples with proper Ag concentration. Possible mechanism was elucidated by means of the morphology and distribution of Ag additives throughout the ZnO host.
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81.07.Bc Nanocrystalline materials
73.63.Bd Nanocrystalline materials
85.30.-z Semiconductor devices

Assessment of thermoelectric performance of Cu2ZnSnX4, X = S, Se, and Te

C. Sevik and T. Çağın

Appl. Phys. Lett. 95, 112105 (2009); http://dx.doi.org/10.1063/1.3222862 (3 pages) | Cited 18 times

Online Publication Date: 16 September 2009

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A recent experiment on In-doped Cu2ZnSnSe4 [ X. Y. Shi et al., Appl. Phys. Lett. 94, 122103 (2009) ] has shown promising thermoelectric performance characteristics. In this letter, we analyze relevant electronic and transport properties of Cu2ZnSnSe4 and similar compounds, Cu2ZnSnS4 and Cu2ZnSnTe4, to assess their potential as thermoelectric materials. Using density functional theory and Boltzmann transport equations, we determine Seebeck coefficients, conductivities, and power factors of closely related polymorphs with space groups, Imath, Imath2m, and Pmath2m for each compound. Based on their electronic structure and transport properties, we conclude that other two compounds could have similar potential as thermoelectric materials.
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72.15.Jf Thermoelectric and thermomagnetic effects
71.20.Be Transition metals and alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Transmission electron microscopy investigation of inversion domain boundary in Al0.65Ga0.35N grown on AlN/sapphire template

L. W. Sang, H. Fang, Z. X. Qin, X. Q. Wang, B. Shen, Z. J. Yang, G. Y. Zhang, X. P. Zhang, L. P. You, and D. P. Yu

Appl. Phys. Lett. 95, 112106 (2009); http://dx.doi.org/10.1063/1.3231443 (3 pages) | Cited 2 times

Online Publication Date: 17 September 2009

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A kind of inversion domains (IDs) which originated from the tips of threading dislocations were observed in the Al0.65Ga0.35N layer by transmission electron microscopy (TEM). The IDs showed columnar structures with diameters of 10–20 nm. We find that the dislocations evolved into V-shape boundaries then form IDs. By high resolution TEM analysis, the atomic structure at the boundary was proved to be the IDB∗ structure, in which each atom remains fourfold coordinated without the formation of Ga–Ga or N–N bonds.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Defect-free single-crystal Ge island arrays on insulator by rapid-melting-growth combined with seed-positioning technique

Kaoru Toko, Takashi Sakane, Takanori Tanaka, Taizoh Sadoh, and Masanobu Miyao

Appl. Phys. Lett. 95, 112107 (2009); http://dx.doi.org/10.1063/1.3231925 (3 pages) | Cited 9 times

Online Publication Date: 18 September 2009

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Single-crystal Ge island arrays on SiO2/Si structures are desired to merge advanced Ge devices into Si large scale integrated circuit (LSI). We have developed the rapid-melting-growth process of amorphous Ge by using Ni-imprint-induced Si (111) fine crystals ( ∼ 1 μmϕ) as the growth seed. Arrays of (111) oriented single-crystal Ge islands with device size ( ∼ 10 μmϕ) are uniformly fabricated on SiO2/Si substrates. The cross-sectional transmission electron microscopy observation reveals that Ge islands include no dislocation or stacking fault. This method opens up a possibility to achieve hybrid SiGe-LSI with multifunctions.
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81.10.Fq Growth from melts; zone melting and refining
61.72.Nn Stacking faults and other planar or extended defects

Time-resolved luminescence studies of proton-implanted GaN

A. Pinos, S. Marcinkevičius, M. Usman, and A. Hallén

Appl. Phys. Lett. 95, 112108 (2009); http://dx.doi.org/10.1063/1.3226108 (3 pages) | Cited 7 times

Online Publication Date: 18 September 2009

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Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose of 1×1015 cm−2, decreases down to a few picoseconds. With annealing at temperatures between 250 and 750 °C, carrier lifetime, contrary to electrical characteristics, is only slightly restored, indicating that electrical compensation and carrier dynamics are governed by different defects. Ga vacancies, free and bound at threading dislocations, are suggested as the most probable defects, responsible for electrical compensation and carrier lifetime quenching.
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78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence
61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Spectroscopic study of V doped Hg0.018Cd0.981Mn0.001Te bulk crystals as near-infrared materials for optical applications

Yu. P. Gnatenko, P. M. Bukivskij, Yu. P. Piryatinski, I. O. Faryna, O. A. Shigiltchoff, and R. V. Gamernyk

Appl. Phys. Lett. 95, 112109 (2009); http://dx.doi.org/10.1063/1.3226670 (3 pages) | Cited 2 times

Online Publication Date: 18 September 2009

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It was shown that the photosensitivity region of the semi-insulating V doped Hg0.018Cd0.981Mn0.001Te crystals extends up to 1800 nm and is caused by the electron photogeneration resulting in the transitions from the main 4T1(F) state to the excited 4A2(F)- and 4T1(P) states of V2+ ions, which are in resonance with the conduction band. The electronic processes in the crystals are fast and correspond to the nanosecond region. Codoping by the Mn atoms leads to considerable improvement their optical quality and increase the resistivity. The obtained results indicate that such crystals can be considered as promising near-infrared materials for various optical applications.
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78.30.Er Solid metals and alloys
71.20.Gj Other metals and alloys
61.72.up Other materials

The reason for the increased threshold switching voltage of SiO2 doped Ge2Sb2Te5 thin films for phase change random access memory

Seung Wook Ryu, Jong Ho Lee, Young Bae Ahn, Choon Hwan Kim, Bong Seob Yang, Gun Hwan Kim, Soo Gil Kim, Se-Ho Lee, Cheol Seong Hwang, and Hyeong Joon Kim

Appl. Phys. Lett. 95, 112110 (2009); http://dx.doi.org/10.1063/1.3232237 (3 pages) | Cited 7 times

Online Publication Date: 18 September 2009

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This study examined the threshold switching voltage (VT) of 150 nm thick SiO2 doped Ge2Sb2Te5 (SGST) films for phase change random access memory applications. The VT of the SGST films increased from ∼ 0.9 V (for GST) to ∼ 1.5 V with increasing SiO2 content. The optical band gap and Urbach edge of the SGST films were similar regardless of the SiO2 concentration. The dielectric constant decreased by ∼ 37% and the electrical resistivity increased by ∼ 19%. The increase in VT of SGST films is associated with an effective increase in electric field and the decreased generation rate caused by impact ionization.
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85.30.-z Semiconductor devices
84.30.Sk Pulse and digital circuits
73.61.Le Other inorganic semiconductors
73.50.Fq High-field and nonlinear effects
77.22.Ch Permittivity (dielectric function)

Ferromagnetism in Cu-doped AlN films

Fan-Yong Ran, M. Subramanian, Masaki Tanemura, Yasuhiko Hayashi, and Takehiko Hihara

Appl. Phys. Lett. 95, 112111 (2009); http://dx.doi.org/10.1063/1.3232238 (3 pages) | Cited 10 times

Online Publication Date: 18 September 2009

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AlN films doped with 3.2–8.2 at. % Cu were deposited by helicon magnetron sputtering. The films exhibited ferromagnetism with a Curie temperature above 360 K. The observed magnetic anisotropy and exclusion of ferromagnetic contamination indicated that the ferromagnetism was the intrinsic property of Cu-doped AlN films. Room-temperature (RT) saturation magnetization (Ms) tended to decrease with increasing Cu concentration and the maximum RT Ms obtained was about 8.5 emu/cm3 (0.6 μB/Cu). Vacuum annealing increased the RT Ms values and meanwhile reduced ratio of N/(Al+Cu), which suggested that Al interstitial and N vacancy might contribute to the observed ferromagnetic behavior.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
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