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10 Nov 2008

Volume 93, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages)

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton
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Diffusion of electron-hole pairs in disordered quantum wires

N. Moret, D. Y. Oberli, B. Dwir, A. Rudra, and E. Kapon

Appl. Phys. Lett. 93, 192101 (2008); http://dx.doi.org/10.1063/1.2970987 (3 pages) | Cited 7 times

Online Publication Date: 10 November 2008

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The diffusivity of photogenerated electron-hole pairs in weakly disordered GaAs/AlGaAs V-groove quantum wires was measured using a photoluminescence (PL) time-of-flight technique. It is shown that the electron-hole pair diffusion is thermally activated above about 50 K. Exciton localization is observed in micro-PL (μPL) spectra at low temperature. A reduction in the Stokes shift is found to accompany the increase in the diffusion coefficient. Nevertheless, localization-related features in the μPL spectra disappear at intermediate temperatures, before measurable diffusion occurs.
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71.35.-y Excitons and related phenomena
73.21.Hb Quantum wires
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Light transmittance memory effect of lead lanthanum zirconate titanate induced by the electrical imprint field

Toshinori Ohashi, Hiroshi Hosaka, and Takeshi Morita

Appl. Phys. Lett. 93, 192102 (2008); http://dx.doi.org/10.1063/1.3021068 (3 pages) | Cited 1 time

Online Publication Date: 10 November 2008

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The possibility of inducing a light transmittance memory effect in a ferroelectric material was investigated. Lead lanthanum zirconate titanate was examined for a light transmittance memory effect, and it was confirmed that the light transmittance had two stable values in the absence of an electrical field after control of the imprint electrical field. This memory effect was demonstrated as an optical shutter under pulsed voltage operation, resulting in decreased energy consumption and simple operation.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Reverse graded relaxed buffers for high Ge content SiGe virtual substrates

V. A. Shah, A. Dobbie, M. Myronov, D. J. F. Fulgoni, L. J. Nash, and D. R. Leadley

Appl. Phys. Lett. 93, 192103 (2008); http://dx.doi.org/10.1063/1.3023068 (3 pages) | Cited 21 times

Online Publication Date: 10 November 2008

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An innovative approach is proposed for epitaxial growth of high Ge content, relaxed Si1−xGex buffer layers on a Si(001) substrate. The advantages of the technique are demonstrated by growing such structures via chemical vapor deposition and their characterization. Relaxed Ge is first grown on the substrate followed by the reverse grading approach to reach a final buffer composition of 0.78. The optimized buffer structure is only 2.8 μm thick and demonstrates a low surface threading dislocation density of 4×106 cm−2, with a surface roughness of 2.6 nm. The buffers demonstrate a relaxation of up to 107%.
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68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.bg Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of structural anisotropy on electronic conduction in delafossite tin doped copper indium oxide thin films

Mandeep Singh and B. R. Mehta

Appl. Phys. Lett. 93, 192104 (2008); http://dx.doi.org/10.1063/1.2982915 (3 pages) | Cited 2 times

Online Publication Date: 11 November 2008

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Sn doped CuInO2 thin films having a single delafossite phase have been synthesized by magnetron sputtering technique. A gradual decrease in the activation energy from 0.43 to about 0.10 eV and a large increase in conductivity are observed in Sn doped samples with increasing fraction of crystallites having (006) orientation due to an increase in substrate temperature. Due to thermally activated carrier transport along O-A-O layers and activated carrier generation along BO6 layers, crystallite orientation becomes a crucial factor in controlling the conduction in delafossite thin films.
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73.61.Ng Insulators
61.72.up Other materials
68.55.J- Morphology of films
81.15.Cd Deposition by sputtering
73.50.Dn Low-field transport and mobility; piezoresistance

Band offsets between Si and epitaxial rare earth sesquioxides (RE2O3, RE = La,Nd,Gd,Lu): Effect of 4f-shell occupancy

V. V. Afanas’ev, M. Badylevich, A. Stesmans, A. Laha, H. J. Osten, A. Fissel, W. Tian, L. F. Edge, and D. G. Schlom

Appl. Phys. Lett. 93, 192105 (2008); http://dx.doi.org/10.1063/1.3003872 (3 pages) | Cited 3 times

Online Publication Date: 11 November 2008

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Internal photoemission of electrons and holes into cubic Nd2O3 epitaxially grown on (100)Si reveals a significant contribution of Nd 4f states to the spectrum of the oxide gap states. In contrast to oxides of other rare earth (RE) elements (Gd, Lu) epitaxially grown in the same cubic polymorph, to hexagonal LaLuO3, and to polycrystalline HfO2, the occupied Nd 4f states produce an additional filled band 0.8 eV above the O 2p derived valence band. The unoccupied portion of the Nd 4f shell leads to empty electron states in the energy range of 1 eV below the RE 5d derived oxide conduction band. The exposed Nd 4f states suggest the possibility to use this metal and, possibly, other REs with low f-shell occupancy to control the interface band offsets by selective interface doping.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Electrical characteristics of contacts to thin film N-polar n-type GaN

Hyunsoo Kim, Jae-Hyun Ryou, Russell D. Dupuis, Sung-Nam Lee, Yongjo Park, Joon-Woo Jeon, and Tae-Yeon Seong

Appl. Phys. Lett. 93, 192106 (2008); http://dx.doi.org/10.1063/1.3013838 (3 pages) | Cited 23 times

Online Publication Date: 11 November 2008

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The electrical characteristics of metallization contacts to a thin film N-polar n-type GaN layer fabricated by a laser lift-off process combined with a dry etching are investigated. It is shown that for Pt Schottky contacts, the Schottky barrier height of the N-polar GaN is 1.27 eV, which is larger than that (1.23 eV) of reference Ga-polar GaN. Ti/Al Ohmic contacts to the N-polar GaN experience thermal degradation even at 400 °C. Such annealing-induced degradation is explained in terms of the presence of the complex surface states of the N-polar GaN, which consists of impurities and process-induced donorlike and acceptorlike defects.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ey III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Defect passivation and homogenization of amorphous oxide thin-film transistor by wet O2 annealing

Kenji Nomura, Toshio Kamiya, Hiromichi Ohta, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 93, 192107 (2008); http://dx.doi.org/10.1063/1.3020714 (3 pages) | Cited 52 times

Online Publication Date: 11 November 2008

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Roles of H2O addition to an annealing atmosphere were investigated for amorphous In–Ga–Zn–O thin-film transistors fabricated at room temperature. Although dry O2 annealing improved saturation mobility (μsat) and subthreshold voltage swings (S), wet O2 annealing further improved them to μsat ∼ 12 cm2(V s)−1 and S<0.12 V  decade−1 along with improvement of their uniformity. Desorption of OH-related species caused conductivity increase during thermal annealing at <310 °C. Zn–O components started to desorb at ∼ 300 °C for the unannealed and the dry O2 annealed films, while these were suppressed remarkably by the wet O2 annealing.
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85.30.Tv Field effect devices

Effect of dislocations on electrical and optical properties of n-type Al0.34Ga0.66N

K. X. Chen, Q. Dai, W. Lee, J. K. Kim, E. F. Schubert, J. Grandusky, M. Mendrick, X. Li, and J. A. Smart

Appl. Phys. Lett. 93, 192108 (2008); http://dx.doi.org/10.1063/1.3021076 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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The effect of edge and screw dislocations on the electrical and optical properties of n-type Al0.34Ga0.66N is investigated. It is found that edge dislocations strongly affect the electrical properties of n-type Al0.34Ga0.66N. Both free carrier concentration and mobility decrease with increasing edge dislocation density. Edge dislocations also enhance nonradiative recombination, which is indicated by decreasing near-band-edge UV as well as parasitic blue photoluminescence. The UV/blue ratio is found to be independent of the edge dislocation density but strongly depends on the Si doping concentration.
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78.55.Cr III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors

In situ heat treatment of ultrathin MgO layer for giant magnetoresistance ratio with low resistance area product in CoFeB/MgO/CoFeB magnetic tunnel junctions

Shinji Isogami, Masakiyo Tsunoda, Kojiro Komagaki, Kazuyuki Sunaga, Yuji Uehara, Masashige Sato, Toyoo Miyajima, and Migaku Takahashi

Appl. Phys. Lett. 93, 192109 (2008); http://dx.doi.org/10.1063/1.3021372 (3 pages) | Cited 16 times

Online Publication Date: 11 November 2008

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In order to promote the grain growth of ultrathin MgO barrier deposited on a CoFeB layer, in situ infrared (IR) heat treatment just after the deposition of MgO barrier was examined. In case that IR heat treatment was not applied, tunneling magnetoresistance (TMR) ratio of CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) was significantly decreased with decreasing resistance area (RA) product to less than 10 Ω μm2. On the other hand, TMR ratio of 206% was achieved at the RA product of 2.1 Ω μm2 when the IR heat treatment was applied. According to the cross sectional transmission electron microscope images for the samples with 0.76-nm-thick ( ∼ 4 ML) MgO barrier, the (001) oriented well crystallized structure with smooth interface was observed for the IR heated sample. Moreover, it revealed that the lateral grain size of MgO was significantly enlarged compared to that for the sample without IR heating. The improvement of TMR properties at low RA product region by the heat treatment might be due to the decrease in grain boundaries of MgO layer where the coherent tunneling of Δ1 electrons is not restricted.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.72.Mm Grain and twin boundaries
75.47.De Giant magnetoresistance
81.40.Gh Other heat and thermomechanical treatments
75.70.Ak Magnetic properties of monolayers and thin films

Surface states and origin of the Fermi level pinning on nonpolar GaN(1math00) surfaces

L. Ivanova, S. Borisova, H. Eisele, M. Dähne, A. Laubsch, and Ph. Ebert

Appl. Phys. Lett. 93, 192110 (2008); http://dx.doi.org/10.1063/1.3026743 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2008

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GaN(1math00) cleavage surfaces were investigated by cross-sectional scanning tunneling microscopy and spectroscopy. It is found that both the N and Ga derived intrinsic dangling bond surface states are outside of the fundamental band gap. Their band edges are both located at the math point of the surface Brillouin zone. The observed Fermi level pinning at 1.0 eV below the conduction band edge is attributed to the high step and defect density at the surface but not to intrinsic surface states.
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73.20.At Surface states, band structure, electron density of states
68.47.Fg Semiconductor surfaces
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Carrier recombination lifetime characterization of molecular beam epitaxially grown HgCdTe

Y. Chang, C. H. Grein, J. Zhao, C. R. Becker, M. E. Flatte, P.-K. Liao, F. Aqariden, and S. Sivananthan

Appl. Phys. Lett. 93, 192111 (2008); http://dx.doi.org/10.1063/1.3001935 (3 pages) | Cited 6 times

Online Publication Date: 13 November 2008

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Carrier recombination lifetime measurements and analyses based on Shockley–Read–Hall, radiative, and Auger recombination mechanisms were utilized to characterize the material quality of HgCdTe grown by molecular beam epitaxy. The Auger recombination mechanism employed in this analysis is in the theoretical framework according to Beattie and Landsberg [Proc. R. Soc. London, Ser. A 249, 16 (1959) ], which we independently re-evaluated using the electronic band structures computed with a 14-band k⋅p methodology and direct evaluations of the transition rates. The Levenberg–Marquette method was used to fit the temperature-dependent carrier recombination lifetimes as measured by the photoconductive decay technique. Based on the above methods, carrier recombination lifetime measurements were developed as a routine characterization technique.
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71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

20-nm-gate-length erbium-/platinum-silicided n-/p-type Schottky barrier metal-oxide-semiconductor field-effect transistors

Moongyu Jang, Cheljong Choi, and Seongjae Lee

Appl. Phys. Lett. 93, 192112 (2008); http://dx.doi.org/10.1063/1.3025726 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2008

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20-nm-gate-length erbium-/platinum-silicided n-/p-type Schottky barrier metal-oxide-semiconductor field-effect transistors (SB-MOSFETs) were manufactured. The manufactured 20-nm-gate-length n-/p-type SB-MOSFETs showed large on/off current ratio (>106) with low leakage current less than 10−5 μA/μm due to the existence of the Schottky barrier between source and channel region. The saturation currents were 550 and −376 μA/μm when drain and gate voltages are 2/−2 and 3/−3 V, for the n-/p-type SB-MOSFET, respectively.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

The effect of TiO2 nanoparticle concentration on conduction mechanism for TiO2-polymer diode

K. H. Yoo, K. S. Kang, Y. Chen, K. J. Han, and Jaehwan Kim

Appl. Phys. Lett. 93, 192113 (2008); http://dx.doi.org/10.1063/1.3005591 (3 pages) | Cited 2 times

Online Publication Date: 14 November 2008

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Polymer Schottky diodes using p-type poly(3,4-ethylenedioxythiophene:poly (styrenesulfonate) (PEDOT:PSS) doped with various concentrations of n-type TiO2 nanoparticles have been fabricated. Although Al/PEDOT:PSS/Au Schottky diode does not show a clear diode characteristics, the Al/TiO2-PEDOT:PSS/Au Schottky diode exhibites excellent rectification characteristics. A Schottky diode with highly doped TiO2 nanoparticles (20 wt %) shows high forward current having more than three orders of magnitude with respect to pristine PEDOT:PSS Schottky diode. The conduction mechanism of the TiO2 doped Schottky diodes shows best fit of space charge limited conduction process compared to the other mechanisms including Schottky emission and Poole–Frenkel emission.
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85.30.Kk Junction diodes

Structural and transport properties of epitaxial niobium-doped BaTiO3 films

Y. Shao, R. A. Hughes, A. Dabkowski, G. Radtke, W. H. Gong, J. S. Preston, and G. A. Botton

Appl. Phys. Lett. 93, 192114 (2008); http://dx.doi.org/10.1063/1.3025434 (3 pages) | Cited 3 times

Online Publication Date: 14 November 2008

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BaTi1−xNbxO3 films, spanning the entire range of x, have been deposited on MgAl2O4 substrates. X-ray diffraction measurements indicate single phase films for all values of x, contrary to a previously reported niobium solubility limit. Films show extreme sensitivity to high temperature oxygen exposure, which destroys conductivity and severely disrupts crystallinity. Under optimum growth conditions increasing x gives rise to a Ti4+ to Ti3+ transformation in the oxidation state accompanied by increased conductivity with a semiconductor-metal transition near x = 0.2. Temperature dependent magnetic measurements show an anomalous rise in the spin moment, a feature supportive of the small singlet bipolaron model.
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73.61.Ng Insulators
68.55.-a Thin film structure and morphology
64.75.Bc Solubility
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Ak Magnetic properties of monolayers and thin films

Effective surface passivation methodologies for high performance germanium metal oxide semiconductor field effect transistors

H. J. Na, J. C. Lee, D. Heh, P. Sivasubramani, P. D. Kirsch, J. W. Oh, P. Majhi, S. Rivillon, Y. J. Chabal, B. H. Lee, and R. Choi

Appl. Phys. Lett. 93, 192115 (2008); http://dx.doi.org/10.1063/1.3028025 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2008

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We demonstrate methodologies to improve the interface characteristics between a germanium (Ge) substrate and high-k gate dielectrics. GeON and SiOx were investigated as passivating layers on a Ge surface. Smaller hysteresis and interface state density (Dit) were obtained using SiOx interface layer and p-type metal oxide semiconductor field effect transistors (MOSFETs) fabricated with a gate stack of Ge/SiOx/HfSiO/WN showed about two times higher effective mobility compared to universal Si/SiO2 MOSFET. Because the formation of GeOx at the interface resulted in higher hysteresis and equivalent oxide thickness, the effective suppression of growth of unstable GeOx by SiOx interface layer contributed to the good device characteristics of the fabricated devices.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
81.65.Rv Passivation

Single shot measurement of a silicon single electron transistor

D. G. Hasko, T. Ferrus, Q. R. Morrissey, S. R. Burge, E. J. Freeman, M. J. French, A. Lam, L. Creswell, R. J. Collier, D. A. Williams, and G. A. D. Briggs

Appl. Phys. Lett. 93, 192116 (2008); http://dx.doi.org/10.1063/1.3028344 (3 pages) | Cited 7 times

Online Publication Date: 14 November 2008

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We have fabricated a custom cryogenic complementary metal-oxide-semiconductor integrated circuit that has a higher measurement bandwidth compared to conventional room temperature electronics. This allowed implementing single shot operations and observe the real-time evolution of the current of a phosphorus-doped silicon single electron transistor that was irradiated with a microwave pulse. Relaxation times up to 90 μs are observed, suggesting the presence of well isolated electron excitations within the device. It is expected that these are associated with long decoherence time and the device may be suitable for quantum information processing.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
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