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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages)

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng
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Bipolar conductivity in nanocrystallized TiO2

D. R. Islamov, V. A. Gritsenko, C. H. Cheng, and A. Chin

Appl. Phys. Lett. 101, 032101 (2012); http://dx.doi.org/10.1063/1.4737016 (2 pages)

Online Publication Date: 16 July 2012

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This study calculated the contribution of electrons and holes to TiO2 conductivity in Si/TiO2/Ni structures by conducting experiments on the injection of minority carriers from n- and p-type silicon. Results show that electrons and holes contribute to the conductivity of TiO2, enabling two-band conductivity.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-efficiency heterojunction solar cells on crystalline germanium substrates

Bahman Hekmatshoar, Davood Shahrjerdi, Marinus Hopstaken, Keith Fogel, and Devendra K. Sadana

Appl. Phys. Lett. 101, 032102 (2012); http://dx.doi.org/10.1063/1.4737166 (4 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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We report stand-alone heterojunction (HJ) solar cells with conversion efficiencies of 5.9% and 7.2% on n-type and p-type crystalline germanium (c-Ge) substrates, respectively. The emitter of the HJ solar cells is formed by growing thin layers of highly doped hydrogenated microcrystalline silicon using plasma-enhanced chemical vapor deposition at temperatures close to 200 °C. The conversion efficiencies of the HJ solar cells are well-comparable with conventional devices fabricated at temperatures as high as 600 °C. We also study the surface passivation of c-Ge with hydrogenated amorphous and microcrystalline Si and correlate the passivation quality with the electrical performance of the HJ solar cells.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells

Nitrogen-polar core-shell GaN light-emitting diodes grown by selective area metalorganic vapor phase epitaxy

Shunfeng Li, Xue Wang, Sönke Fündling, Milena Erenburg, Johannes Ledig, Jiandong Wei, Hergo H. Wehmann, Andreas Waag, Werner Bergbauer, Martin Mandl, Martin Strassburg, Achim Trampert, Uwe Jahn, Henning Riechert, Holger Jönen, et al.

Appl. Phys. Lett. 101, 032103 (2012); http://dx.doi.org/10.1063/1.4737395 (4 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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Homogeneous nitrogen-polar GaN core-shell light emitting diode (LED) arrays were fabricated by selective area growth on patterned substrates. Transmission electron microscopy measurements prove the core-shell structure of the rod LEDs. Depending on the growth facets, the InGaN/GaN multi-quantum wells (MQWs) show different dimensions and morphology. Cathodoluminescence (CL) measurements reveal a MQWs emission centered at about 415 nm on sidewalls and another emission at 460 nm from top surfaces. CL line scans on cleaved rod also indicate the core-shell morphology. Finally, an internal quantum efficiency of about 28% at room temperature was determined by an all-optical method on a LED array.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Growth direction dependence of the electron spin dynamics in {111} GaAs quantum wells

H. Q. Ye, G. Wang, B. L. Liu, Z. W. Shi, W. X. Wang, C. Fontaine, A. Balocchi, T. Amand, D. Lagarde, P. Renucci, and X. Marie

Appl. Phys. Lett. 101, 032104 (2012); http://dx.doi.org/10.1063/1.4737007 (5 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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The electron spin dynamics is studied by time-resolved Kerr rotation in GaAs/AlGaAs quantum wells embedded in NIP structures grown on (111)A or (111)B-oriented substrates. In both cases the spin lifetimes are significantly increased by applying an external electric field, but this field has to point along the growth direction for structures grown on (111)A and opposite to it for the ones grown on (111)B. This extended electron spin lifetime is the result of the suppression of the D’yakonov-Perel spin relaxation mechanism [Sov. Phys. Solid State 13, 3023 (1972)] due to the cancellation effect of the internal Dresselhaus term [Phys. Rev. 100, 580 (1955)] with the external electric field induced Rashba one [J. Phys. C 17, 6039 (1984)], both governing the conduction band spin-orbit splitting. These results demonstrate the key role played by the growth direction in the design of spintronic devices.
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73.21.Fg Quantum wells
78.20.Jq Electro-optical effects
78.67.De Quantum wells
68.65.Fg Quantum wells

A higher-k tetragonal HfO2 formed by chlorine plasma treatment at interfacial layer for metal-oxide-semiconductor devices

Chung-Hao Fu, Kuei-Shu Chang-Liao, Chen-Chien Li, Zong-Hao Ye, Fang-Ming Hsu, Tien-Ko Wang, Yao-Jen Lee, and Ming-Jinn Tsai

Appl. Phys. Lett. 101, 032105 (2012); http://dx.doi.org/10.1063/1.4737393 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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A tetragonal HfO2 (t-HfO2) with higher-k value and large band gap is investigated in this work. X-ray diffraction analysis shows a t-HfO2 can be formed by using Cl2 plasma treatment at the HfO2/Si interface after a post deposition annealing at 650 °C. The mechanisms of t-HfO2 formation can be attributed to the Si diffusion and oxygen vacancy generation which are formed by Cl2 plasma treatment. From the cross-sectional transmission electron microscope and capacitance-voltage measurement, the k value of this t-HfO2 is estimated to be about 35. The optical band gap value for t-HfO2 is similar to that of the monoclinic.
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84.32.Tt Capacitors

Solitary acoustic pulses in quantum semiconductor plasmas

W. M. Moslem, I. Zeba, and P. K. Shukla

Appl. Phys. Lett. 101, 032106 (2012); http://dx.doi.org/10.1063/1.4736726 (5 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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We report properties of solitary acoustic pulses that propagate in electron-hole quantum semiconductor plasmas. We show that the dynamics of nonlinear acoustic pulses is governed by the Korteweg–de Vries equation, which includes contributions of the electron and hole quantum recoil effects, quantum statistical pressures of the plasma species, as well as exchange and correlation effects. Typical values for GaAs, GaSb, GaN, and InP semiconductors are used to estimate the speed and profiles of solitary acoustic pulses. The nonlinear solitary pulses depict intrinsic localization of electrostatic wave energies in semiconductor plasmas.
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72.30.+q High-frequency effects; plasma effects

Room temperature sub-bandgap photoluminescence from silicon containing oxide precipitates

K. Bothe, R. J. Falster, and J. D. Murphy

Appl. Phys. Lett. 101, 032107 (2012); http://dx.doi.org/10.1063/1.4737175 (4 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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Room temperature photoluminescence was measured from p-type Czochralski silicon processed to contain oxide precipitates. No detectable luminescence was associated with unstrained oxide precipitates. Strained oxide precipitates gave rise to a broad luminescence peak centred at ∼1600 nm. The intensity of the peak increased with the density of strained precipitates, with band-to-band luminescence being reduced correspondingly. Dislocations and stacking faults around the strained precipitates were found to introduce competing non-radiative recombination centres which reduced the sub-bandgap photoluminescence. A mechanism is proposed for the sub-bandgap luminescence due to strained precipitates in terms of a transition between defect bands.
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78.55.-m Photoluminescence, properties and materials
81.05.Cy Elemental semiconductors
81.10.Fq Growth from melts; zone melting and refining
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Applicability of continuum absorption in semiconductor quantum wells to absolute absorption-strength standards

Masahiro Yoshita, Kenji Kamide, Hidekatsu Suzuura, and Hidefumi Akiyama

Appl. Phys. Lett. 101, 032108 (2012); http://dx.doi.org/10.1063/1.4737900 (4 pages)

Online Publication Date: 19 July 2012

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The absolute strength of two-dimensional continuum absorption in semiconductor quantum wells (QWs) was investigated for application to an absorption-strength standard. We presented an equation for the continuum-state absorbance in a QW, showing that the absorbance near the band edge is essentially described by a universal value proportional to the fine-structure constant with correction terms for band-mixing effects and Coulomb enhancement effects. By using k·p equations with the established band parameters, we calculated the absorbance with quantitative estimations of the correction terms in typical semiconductor QWs. The results indicate that the absorbance of the QW is applicable to an absorption-strength standard.
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78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors

Ultra-low resistance ohmic contacts to GaN with high Si doping concentrations grown by molecular beam epitaxy

Faiza Afroz Faria, Jia Guo, Pei Zhao, Guowang Li, Prem Kumar Kandaswamy, Mark Wistey, Huili (Grace) Xing, and Debdeep Jena

Appl. Phys. Lett. 101, 032109 (2012); http://dx.doi.org/10.1063/1.4738768 (4 pages)

Online Publication Date: 20 July 2012

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Ti/Al/Ni/Au ohmic contacts were formed on heavily doped n+ metal-polar GaN samples with various Si doping concentrations grown by molecular beam epitaxy. The contact resistivity (RC) and sheet resistance (Rsh) as a function of corresponding GaN free carrier concentration (n) were measured. Very low RC values (<0.09 Ω mm) were obtained, with a minimum RC of 0.035 Ω mm on a sample with a room temperature carrier concentration of ∼5 × 1019 cm−3. Based on the systematic study, the role of RC and Rsh is discussed in the context of regrown n+ GaN ohmic contacts for GaN based high electron mobility transistors.
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73.40.Ns Metal-nonmetal contacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
73.40.Cg Contact resistance, contact potential
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