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21 Sep 2009

Volume 95, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 95, 121104 (2009); http://dx.doi.org/10.1063/1.3231448 (3 pages)

E. H. Khoo, I. Ahmed, and E. P. Li
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Theoretical design of GaN/ferroelectric heterostructure: Toward a strained semiconductor on ferroelectrics

Jihua Zhang (张继华), Chuanren Yang (杨传仁), Song Wu (吴松), Ying Liu (刘颖), Hongwei Chen (陈宏伟), Wanli Zhang (张万里), and Yanrong Li (李言荣)

Appl. Phys. Lett. 95, 122101 (2009); http://dx.doi.org/10.1063/1.3231072 (3 pages) | Cited 2 times

Online Publication Date: 21 September 2009

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Ferroelectric/semiconductor heterostructures are of great interest for future electronic devices. This letter examined the material parameters and carrier distributions of an AlGaN(0001)/GaN(0001)/BaTiO3(111) double heterostructure by combining first principles and charge control model. Results show that in the optimized case, there will appear two channels in GaN layer, and the sheet electron density will be doubled compared to conventional AlGaN/GaN heterojunction. A possible device structure was proposed to make the channel become switchable and reduce the source/drain resistance. This strained semiconductor on ferroelectric structure may be promising for high speed power devices.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.80.-e Ferroelectricity and antiferroelectricity
72.20.Dp General theory, scattering mechanisms
72.80.Ey III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds

Hall effect mobility of epitaxial graphene grown on silicon carbide

J. L. Tedesco, B. L. VanMil, R. L. Myers-Ward, J. M. McCrate, S. A. Kitt, P. M. Campbell, G. G. Jernigan, J. C. Culbertson, C. R. Eddy, Jr., and D. K. Gaskill

Appl. Phys. Lett. 95, 122102 (2009); http://dx.doi.org/10.1063/1.3224887 (3 pages) | Cited 36 times

Online Publication Date: 21 September 2009

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Epitaxial graphene (EG) films were grown in vacuo by silicon sublimation from the (0001) and (000math) faces of 4H-SiC and 6H-SiC. Hall effect mobilities and sheet carrier densities of the films were measured at 300 and 77 K and the data depended on the growth face. About 40% of the samples exhibited holes as the dominant carrier, independent of face. Generally, mobilities increased with decreasing carrier density, independent of carrier type and substrate polytype. The contributions of scattering mechanisms to the conductivities of the films are discussed. The results suggest that for near-intrinsic carrier densities at 300 K epitaxial graphene mobilities will be ∼ 150 000 cm2 V−1 s−1 on the (000math) face and ∼ 5800 cm2 V−1 s−1 on the (0001) face.
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68.55.at Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.25.+i Surface conductivity and carrier phenomena

Evidence for existence of deep acceptor levels in SiGe-on-insulator substrate fabricated using Ge condensation technique

Haigui Yang, Dong Wang, and Hiroshi Nakashima

Appl. Phys. Lett. 95, 122103 (2009); http://dx.doi.org/10.1063/1.3234373 (3 pages) | Cited 4 times

Online Publication Date: 21 September 2009

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By back-gate metal-oxide-semiconductor field-effect transistor method, we examined acceptor concentration (NA) in nondoped SiGe-on-insulator (SGOI) substrates fabricated using Ge condensation. We found NA’s were much higher than the hole concentration (p) measured by Hall effect for low-Ge% SGOI, while NA’s were almost the same as p for high-Ge% SGOI. Such different behaviors between NA and p as a function of Ge% are closely related to the existence of deep acceptor levels (ETA) in SGOI and ETA energy shift toward valence band with increasing in Ge%, which was confirmed from the temperature dependence of p.
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85.30.Tv Field effect devices
71.55.-i Impurity and defect levels
72.20.My Galvanomagnetic and other magnetotransport effects
73.20.At Surface states, band structure, electron density of states

Chemical structure of the (Zn1−x,Mgx)O/CuIn(S,Se)2 interface in thin film solar cells

F. Erfurth, B. Hußmann, A. Schöll, F. Reinert, A. Grimm, I. Lauermann, M. Bär, Th. Niesen, J. Palm, S. Visbeck, L. Weinhardt, and E. Umbach

Appl. Phys. Lett. 95, 122104 (2009); http://dx.doi.org/10.1063/1.3230071 (3 pages) | Cited 5 times

Online Publication Date: 21 September 2009

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The formation of the interface between a magnetron sputtered (Zn1−x,Mgx)O buffer layer and a CuIn(S,Se)2 absorber in thin film solar cells has been investigated by x-ray photoelectron spectroscopy and x-ray induced Auger electron spectroscopy. Detailed analysis of the spectra shows the incorporation of Zn into the absorber surface in the initial stage of the deposition process forming ZnS and/or ZnSe bonds. As a result we find the buffer layer to be Zn-depleted near the interface.
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84.60.Jt Photoelectric conversion
68.35.Ct Interface structure and roughness
79.20.Fv Electron impact: Auger emission
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Cd Deposition by sputtering

Application of secondary electron potential contrast on junction leakage isolation

Po-Tsun Liu, Jeng-Han Lee, Y. S. Huan, and David Su

Appl. Phys. Lett. 95, 122105 (2009); http://dx.doi.org/10.1063/1.3233963 (3 pages) | Cited 1 time

Online Publication Date: 23 September 2009

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Secondary electron potential contrast (SEPC) technology with an in situ dynamic trigger was studied to inspect P+/N-well junction leakage arising from P-well misalignment in a static random access memory cell. Combining SEPC with scanning electron microscopy observations allows direct identification of the junction shift. Furthermore, an in situ negative bias applied to the P-well can create a wider depletion region and eliminate the leakage path in P+/N-well contacts, allowing the P+/N well to operate normally. This proposed in situ dynamic trigger method is a promising and effective approach to investigating device physics under a dynamic scope.
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84.30.Sk Pulse and digital circuits

Electrical and thermoelectrical properties of SnTe-based films and superlattices

Akihiro Ishida, Tomohiro Yamada, Takuro Tsuchiya, Yoku Inoue, Sadao Takaoka, and Takuji Kita

Appl. Phys. Lett. 95, 122106 (2009); http://dx.doi.org/10.1063/1.3236541 (3 pages) | Cited 2 times

Online Publication Date: 23 September 2009

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SnTe-based films and superlattices (SLs) were prepared and their electrical properties were measured. A EuTe/SnTe SL exhibited a hole mobility of 2720 cm2/V s, which is the highest value reported for any semiconductor material at room temperature. The SnEuTe film also exhibited high hole mobility in contrast to the PbEuTe system. These properties are explained in terms of the band offsets of EuTe/SnTe heterojunction and a decrease in the number of Sn vacancies. In addition, SnTe/PbSe and SnTe/PbS SLs with thin SnTe layers displayed n-type conduction with Seebeck coefficients comparable to those for PbSe and PbS. These properties reflect the type II heterostructures.
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73.21.Cd Superlattices
68.55.ag Semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.61.Le Other inorganic semiconductors
72.80.Jc Other crystalline inorganic semiconductors
61.72.jd Vacancies

Enhanced charge-transport in surfactant-free PbSe quantum dot films grown by a laser-assisted spray process

G. Dedigamuwa, J. Lewis, J. Zhang, X. Jiang, P. Mukherjee, and S. Witanachchi

Appl. Phys. Lett. 95, 122107 (2009); http://dx.doi.org/10.1063/1.3233926 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2009

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A laser-assisted spray process was developed to deposit surfactant-free PbSe quantum dot (QD) films directly on a substrate. These QDs are in close contacts with each other, forming a percolation path for charge transport. Absorption spectroscopy confirmed the quantum confinement of the deposited particles. Room temperature current-voltage measurements across a 2 μm tunnel junction formed by the QDs produced a power-law dependence of the form I∝V2.25, which describes a percolation path of dimensionality slightly above two dimensions. Temperature dependent conductance studies showed thermally activated transport at high temperatures and temperature independent tunneling, followed by previously unobserved metallic conduction at low temperatures.
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68.55.ag Semiconductors
81.15.Rs Spray coating techniques
72.20.-i Conductivity phenomena in semiconductors and insulators
66.70.Df Metals, alloys, and semiconductors
73.40.Gk Tunneling
73.61.Le Other inorganic semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Three-dimensional simulations of a thin film heterojunction solar cell with a point contact/defect passivation structure at the heterointerface

N. Allsop, R. Nürnberg, M. Ch. Lux-Steiner, and Th. Schedel-Niedrig

Appl. Phys. Lett. 95, 122108 (2009); http://dx.doi.org/10.1063/1.3233962 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2009

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Thin film heterojunction solar cells such as those based on the chalcopyrites or amorphous silicon are often limited by interface recombination at the active heterointerface. A new strategy to overcome this limitation is described, replacing the conventional wider band gap contact material with a combination of a passivation layer plus the conventional contact in a point contact type structure. This is similar to the established method to minimize rear contact recombination in crystalline silicon solar cells. Here point contacts at the heterointerface of a CuInS2 based solar cell are modeled using the WIAS-TeSCA code. The importance of the donor defect energy level at the absorber/passivation interface is shown, and a way to improve the cell efficiency by >25% (relative) is outlined.
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84.60.Jt Photoelectric conversion
85.30.Hi Surface barrier, boundary, and point contact devices
81.65.Rv Passivation

Strain dependence of hole effective mass and scattering mechanism in strained Ge channel structures

K. Sawano, K. Toyama, R. Masutomi, T. Okamoto, N. Usami, K. Arimoto, K. Nakagawa, and Y. Shiraki

Appl. Phys. Lett. 95, 122109 (2009); http://dx.doi.org/10.1063/1.3229998 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2009

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Strain dependence of hole effective mass (m∗) in the strained Ge channel was systematically studied, and monotonic m∗ reduction by more than 20% was clearly observed when the strain increased from 0.8% up to 2.8%. The scattering mechanism, which strongly depended on the modulation-doping structure as well as strains, was also investigated based on the Dingle ratio evaluation, and the interface roughness scattering was found to be effectively suppressed by adopting the inverted structure even for the largely strained channels.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Ee Mobility edges; hopping transport
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
68.35.Ct Interface structure and roughness
72.80.Cw Elemental semiconductors

Phonons in Ge nanowires

H. Peelaers, B. Partoens, and F. M. Peeters

Appl. Phys. Lett. 95, 122110 (2009); http://dx.doi.org/10.1063/1.3236526 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2009

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The phonon spectra of thin freestanding, hydrogen passivated, Ge nanowires are calculated by ab initio techniques. The effect of confinement on the phonon modes as caused by the small diameters of the wires is investigated. Confinement causes a hardening of the optical modes and a softening of the longitudinal acoustic modes. The stability of the nanowires, undoped or doped with B or P atoms, is investigated using the obtained phonon spectra. All considered wires were stable, except for highly doped, very thin nanowires.
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63.22.Gh Nanotubes and nanowires
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
62.65.+k Acoustical properties of solids
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si

Quantum pumping with adiabatically modulated barriers in graphene

Rui Zhu and Huiming Chen

Appl. Phys. Lett. 95, 122111 (2009); http://dx.doi.org/10.1063/1.3236785 (3 pages) | Cited 22 times

Online Publication Date: 25 September 2009

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We study the adiabatic quantum pumping characteristics in graphene modulated by two oscillating gate potentials out of phase. The angular and energy dependence of the pumped current (PC) is presented. The direction of the PC can be reversed when a high potential barrier demonstrates stronger transparency than a low one, which results from the Klein paradox. The underlying physics of the pumping process is illuminated.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
73.23.Ad Ballistic transport
81.05.ub Fullerenes and related materials

Large 1/f noise of unipolar resistance switching and its percolating nature

S. B. Lee, S. Park, J. S. Lee, S. C. Chae, S. H. Chang, M. H. Jung, Y. Jo, B. Kahng, B. S. Kang, M.-J. Lee, and T. W. Noh

Appl. Phys. Lett. 95, 122112 (2009); http://dx.doi.org/10.1063/1.3237167 (3 pages) | Cited 14 times

Online Publication Date: 25 September 2009

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We investigated the 1/f noise of Pt/NiO/Pt capacitors that show unipolar resistance switching. When they were switched from the low to high resistance states, the power spectral density of the voltage fluctuation was increased by approximately five orders of magnitude. At 100 K, the relative resistance fluctuation SR/R2 in the low resistance state displayed a power law dependence on the resistance R: i.e., SR/R2∝Rw, where w = 1.6±0.2. This behavior can be explained by percolation theory; however, at higher temperatures or near the switching voltage, SR/R2 becomes enhanced further. This large 1/f noise can be therefore an important problem in the development of resistance random access memory devices.
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84.32.Tt Capacitors
72.70.+m Noise processes and phenomena
84.30.Sk Pulse and digital circuits

Homogeneous linewidth of the 31P bound exciton transition in silicon

A. Yang, M. Steger, T. Sekiguchi, M. L. W. Thewalt, J. W. Ager, III, and E. E. Haller

Appl. Phys. Lett. 95, 122113 (2009); http://dx.doi.org/10.1063/1.3238268 (3 pages) | Cited 5 times

Online Publication Date: 25 September 2009

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The optical transitions of the shallow donor bound exciton associated with phosphorus in silicon are a subject of renewed interest due to the recent discovery that these transitions can be used to both read out and initialize the donor electron and nuclear spin in highly enriched 28Si. The ultimate limit of these processes will be determined by the natural or homogeneous linewidth which we determine here using spectral hole burning. The observed 10 neV linewidth is only four times the limit set by the bound exciton lifetime.
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71.35.-y Excitons and related phenomena
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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