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21 Dec 2009

Volume 95, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 95, 251105 (2009); http://dx.doi.org/10.1063/1.3275666 (3 pages)

D. Stehr, C. M. Morris, D. Talbayev, M. Wagner, H. C. Kim, A. J. Taylor, H. Schneider, P. M. Petroff, and M. S. Sherwin
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Characteristics of surface states and charge neutrality level in Ge

Duygu Kuzum, Koen Martens, Tejas Krishnamohan, and Krishna C. Saraswat

Appl. Phys. Lett. 95, 252101 (2009); http://dx.doi.org/10.1063/1.3270529 (3 pages) | Cited 11 times

Online Publication Date: 21 December 2009

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The characteristics of surface states on Ge are investigated using metal/insulator/semiconductor structures and the conductance technique. Evidence of acceptor-like and donor-like surface states on the valence band side of the Ge bandgap is shown by trap time constant analysis. The dependency of trap time constants on trap energy separation from band edge, capture cross section, and temperature are studied through conductance measurements and simulations. The effect of surface states on the location of charge neutrality level at the Ge surface and the consequences such as surface conductivity and negative charge buildup at the interface are discussed.
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73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors
72.80.Cw Elemental semiconductors
68.47.Fg Semiconductor surfaces
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Enhancement of electroluminescence from TiO2/p+-Si heterostructure-based devices through engineering of oxygen vacancies in TiO2

Yuanyuan Zhang, Xiangyang Ma, Peiliang Chen, Dongsheng Li, Xiaodong Pi, Deren Yang, and P. G. Coleman

Appl. Phys. Lett. 95, 252102 (2009); http://dx.doi.org/10.1063/1.3276547 (3 pages) | Cited 3 times

Online Publication Date: 21 December 2009

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We report that electroluminescence (EL) from TiO2/p+-Si heterostructure-based devices can be significantly enhanced through a prior treatment of TiO2 films in argon (Ar) plasma. It is found that the Ar-plasma treatment introduces excess oxygen vacancies within a certain depth of TiO2 films. The increase in the concentration of oxygen vacancies leads to the enhancement of EL from TiO2/p+-Si heterostructure-based devices because oxygen vacancies are the light-emitting centers. This work demonstrates the use of defect engineering to improve the performance of oxide-based optoelectronic devices.
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78.60.Fi Electroluminescence
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.jd Vacancies
61.72.sd Impurity concentration
68.55.ag Semiconductors

Amorphous hafnium-indium-zinc oxide semiconductor thin film transistors

Chang-Jung Kim, Sangwook Kim, Je-Hun Lee, Jin-Seong Park, Sunil Kim, Jaechul Park, Eunha Lee, Jaechul Lee, Youngsoo Park, Joo Han Kim, Sung Tae Shin, and U-In Chung

Appl. Phys. Lett. 95, 252103 (2009); http://dx.doi.org/10.1063/1.3275801 (3 pages) | Cited 65 times

Online Publication Date: 21 December 2009

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We developed amorphous hafnium-indium-zinc oxide (HIZO) thin films as oxide semiconductors and investigated the films electrically and physically. Adding of hafnium (Hf) element can suppress growing the columnar structure and drastically decrease the carrier concentration and hall mobility in HIZO films. The thin film transistors (TFTs) with amorphous HIZO active channel exhibit good electrical properties with field effect mobility of around 10 cm2/Vs, S of 0.23 V/decade, and high Ion/off ratio of over 108, enough to operate the next electronic devices. In particular, under bias-temperature stress test, the HIZO TFTs with 0.3 mol % (Hf content) showed only 0.46 V shift in threshold voltage, compared with 3.25 V shift in HIZO TFT (0.1 mol %). The Hf ions may play a key role to improve the instability of TFTs due to high oxygen bonding ability. Therefore, the amorphous HIZO semiconductor will be a prominent candidate as an operation device for large area electronic applications.
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85.30.Tv Field effect devices
68.55.ag Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
72.20.Ee Mobility edges; hopping transport

Bandgap engineering of graphene: A density functional theory study

Lei Liu and Zexiang Shen

Appl. Phys. Lett. 95, 252104 (2009); http://dx.doi.org/10.1063/1.3276068 (3 pages) | Cited 24 times

Online Publication Date: 21 December 2009

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Three ways of engineering the bandgap of graphene, i.e., surface bonding, isoelectronic codoping, and alternating electrical/chemical environment, are analyzed with the effective mass approximation and density-functional theory calculations. Surface bonding on graphene would lift its top σ valence bands above π valence states, open a sp3 gap, but also bury the linearly dispersive bands into the valence σ bands. Isoelectronic codoping and asymmetric electrical or chemical environment may open the π−π∗ gap of graphene by breaking its sublattice equivalence. The calculated effective mass versus bandgap may provide useful guidance for the future experimental efforts to fabricate graphene-based semiconductors.
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71.20.Tx Fullerenes and related materials; intercalation compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Why nitrogen cannot lead to p-type conductivity in ZnO

J. L. Lyons, A. Janotti, and C. G. Van de Walle

Appl. Phys. Lett. 95, 252105 (2009); http://dx.doi.org/10.1063/1.3274043 (3 pages) | Cited 87 times

Online Publication Date: 22 December 2009

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Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.
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72.20.Fr Low-field transport and mobility; piezoresistance
71.15.-m Methods of electronic structure calculations
61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors

p-type conduction in beryllium-implanted hexagonal boron nitride films

B. He, W. J. Zhang, Z. Q. Yao, Y. M. Chong, Y. Yang, Q. Ye, X. J. Pan, J. A. Zapien, I. Bello, S. T. Lee, I. Gerhards, H. Zutz, and H. Hofsäss

Appl. Phys. Lett. 95, 252106 (2009); http://dx.doi.org/10.1063/1.3276065 (3 pages) | Cited 3 times

Online Publication Date: 22 December 2009

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p-type conduction in hexagonal boron nitride (hBN) films was achieved by beryllium implantation and subsequent rapid thermal annealing treatment. The dependence of phase composition and electrical properties of hBN films on the implantation fluence and annealing was studied. A maximum resistivity reduction by six orders of magnitude was demonstrated. Hall measurements revealed a corresponding hole concentration of 3×1019 cm−3 and mobility of 27 cm2/V s. The activation energy of Be ions was estimated to be 0.21 eV. It is suggested that hBN is a promising wide bandgap semiconductor for applications in high-temperature electronic devices and transparent conductive coatings.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
66.30.H- Self-diffusion and ionic conduction in nonmetals
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Millisecond flash lamp annealing of shallow implanted layers in Ge

C. Wündisch, M. Posselt, B. Schmidt, V. Heera, T. Schumann, A. Mücklich, R. Grötzschel, W. Skorupa, T. Clarysse, E. Simoen, and H. Hortenbach

Appl. Phys. Lett. 95, 252107 (2009); http://dx.doi.org/10.1063/1.3276770 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2009

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Shallow n+ layers in Ge are formed by phosphorus implantation and subsequent millisecond flash lamp annealing. Present investigations are focused on the dependence of P redistribution, diffusion and electrical activation on heat input into the sample and flash duration. In contrast to conventional annealing procedures an activation up to 6.5×1019 cm−3 is achieved without any dopant redistribution and noticeable diffusion. Present results suggest that independently of pretreatment the maximum activation should be obtained at a flash energy that corresponds to the onset of P diffusion. The deactivation of P is explained qualitatively by mass action analysis which takes into account the formation of phosphorus-vacancy clusters.
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61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.72.sh Impurity distribution
61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.jd Vacancies

Enhanced shot noise in carbon nanotube field-effect transistors

A. Betti, G. Fiori, and G. Iannaccone

Appl. Phys. Lett. 95, 252108 (2009); http://dx.doi.org/10.1063/1.3274128 (3 pages) | Cited 1 time

Online Publication Date: 23 December 2009

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We predict shot noise enhancement in defect-free carbon nanotube field-effect transistors through a numerical investigation based on the self-consistent solution of the Poisson and Schrödinger equations within the nonequilibrium Green’s functions formalism, and on a Monte Carlo approach to reproduce injection statistics. Noise enhancement is due to the correlation between trapping of holes from the drain into quasibound states in the channel and thermionic injection of electrons from the source, and can lead to an appreciable Fano factor of 1.22 at room temperature.
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61.46.Fg Nanotubes
85.30.Tv Field effect devices
03.65.Ge Solutions of wave equations: bound states
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Polarity-dependent resistance switching in GeSbTe phase-change thin films: The importance of excess Sb in filament formation

Ramanathaswamy Pandian, Bart J. Kooi, Jasper L. M. Oosthoek, Pim van den Dool, George Palasantzas, and Andrew Pauza

Appl. Phys. Lett. 95, 252109 (2009); http://dx.doi.org/10.1063/1.3276272 (3 pages) | Cited 10 times

Online Publication Date: 23 December 2009

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We show that polarity-dependent resistance switching in GeSbTe thin films depends strongly on Sb composition by comparing current-voltage characteristics in Sb-excess Ge2Sb2+xTe5 and stoichiometric Ge2Sb2Te5 samples. This type of switching in Ge2Sb2+xTe5 films is reversible with both continuous and pulsed dc voltages less than 1.5 V. Low and high resistance states of this switching can be attributed to formation and rupture, respectively, of electrically conductive Sb-bridges between the Ge2Sb2Te5 crystals and electrodes through the resistive amorphous phase. The coexistence of polarity-dependent resistance switching with amorphous-crystalline phase-changes renders great opportunities to expand the applicability of GeSbTe films for data storage applications.
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68.55.ag Semiconductors
81.05.Gc Amorphous semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
61.66.Bi Elemental solids
61.66.Dk Alloys
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