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13 Aug 2007

Volume 91, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 91, 071906 (2007); http://dx.doi.org/10.1063/1.2753092 (3 pages)

Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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p-type conduction in unintentional carbon-doped ZnO thin films

S. T. Tan, X. W. Sun, Z. G. Yu, P. Wu, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 91, 072101 (2007); http://dx.doi.org/10.1063/1.2768917 (3 pages) | Cited 36 times

Online Publication Date: 14 August 2007

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p-type conduction has been observed in unintentional carbon-doped ZnO thin films grown by metal organic chemical vapor deposition through postgrowth annealing treatment. The existence of carbon, which has been verified by secondary ion mass spectrometry and x-ray photoelectron spectroscopy, was predicted to immobilize the oxygen in the interstitial site in ZnO thin films after annealing. Using first principles calculations, the formation of carbon-oxygen cluster defect in ZnO was found to be favorable and acts as a shallow acceptor. The cryogenic photoluminescence of the p-type carbon-doped ZnO thin films shows an additional peak located at 3.3564 eV, which was attributed to the acceptor (carbon-oxygen cluster defect) bound exciton emission.
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73.61.Ga II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Et II-VI semiconductors
78.60.-b Other luminescence and radiative recombination
78.66.Hf II-VI semiconductors

Thermally driven defect formation and blocking layers at metal-ZnO interfaces

H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, D. C. Look, G. Cantwell, J. Zhang, J. J. Song, and L. J. Brillson

Appl. Phys. Lett. 91, 072102 (2007); http://dx.doi.org/10.1063/1.2772664 (3 pages) | Cited 11 times

Online Publication Date: 16 August 2007

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The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe the temperature-dependent formation of native point defects and reaction layers at metal-ZnO interfaces and their effect on transport properties. These results identify characteristic defect emissions corresponding to metal-Zn alloy versus oxide formation. Au alloys with Zn above its eutectic temperature, while Ta forms oxide blocking layers that reduce current by orders of magnitude at intermediate temperatures. Defects generated at higher temperatures and/or with higher initial defect densities for all interfaces produce Ohmic contacts. These reactions and defect formation with annealing reveal a thermodynamic control of blocking versus Ohmic contacts.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.60.Hk Cathodoluminescence, ionoluminescence

CO2 laser rapid-thermal-annealing SiOx based metal-oxide-semiconductor light emitting diode

Gong-Ru Lin and Chun-Jung Lin

Appl. Phys. Lett. 91, 072103 (2007); http://dx.doi.org/10.1063/1.2769962 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2007

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Structural damage enhanced near-infrared electroluminescence (EL) of a metal-oxide-semiconductor light emitting diode (MOSLED) made on SiOx film with buried nanocrystallite Si after CO2 laser rapid thermal annealing (RTA) at an optimized intensity of 6 kW/cm2 for 1 ms is demonstrated. CO2 laser RTA induced oxygen-related defects are capable of improving Fowler-Nordheim tunneling mechanism of carriers at metal/SiOx interface. The CO2 laser RTA SiOx film reduces Fowler-Nordheim tunneling threshold to 1.8 MV/cm, facilitating an enhanced EL power of an indium tin oxide/SiOx/p-Si/Al MOSLED up to 50 nW at a current density of 2.3 mA/cm2.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices

Electronic transport studies of a systematic series of GaAs/AlGaAs quantum wells

D. R. Luhman, D. C. Tsui, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 91, 072104 (2007); http://dx.doi.org/10.1063/1.2767978 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2007

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The results of experimental transport studies involving a series of five narrow Al0.1Ga0.9As/GaAs quantum wells with well widths ranging from 7.9 to 33.0 nm are reported. The total transport scattering rate measured in thin AlGaAs/GaAs quantum wells is typically limited by electron scattering from the interfacial roughness of the quantum well. For a relatively low constant electron density (ne ∼ 5.8×1010 cm−2), the authors find that interfacial roughness is the dominant scattering mechanism for L ⩽ 16.0 nm and describe the data using a finite quantum well model with adjustable interfacial roughness parameters. Temperature dependence data are also presented.
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73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
68.35.Ct Interface structure and roughness

Study on the synthesis of high quality single crystalline Si1−xGex nanowire and its transport properties

S. J. Whang, S. J. Lee, W. F. Yang, B. J. Cho, and D. L. Kwong

Appl. Phys. Lett. 91, 072105 (2007); http://dx.doi.org/10.1063/1.2772665 (3 pages) | Cited 11 times

Online Publication Date: 17 August 2007

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In this wok, the authors report a synthesis of high quality single crystalline homogeneous Si1−xGex nanowires and investigate the effects of growth temperature on the microstructures, morphologies, and properties of Si1−xGex nanowires. Fabricated phosphorus-doped Si1−xGex nanowire metal-oxide-semiconductor (MOS) field effect transistor integrated with 5 nm HfO2, TaN/Ta metal gate, and Pd source/drain electrode demonstrated enhancement mode p-MOS operation with Ion/Ioff ∼ 104, subthreshold swing of ∼ 136 mV/decade, and small hysteresis of 90 mV.
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81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
73.63.Nm Quantum wires
61.46.Hk Nanocrystals
81.16.-c Methods of micro- and nanofabrication and processing
85.30.Tv Field effect devices

Nitrogen passivation of (0001) 4H-SiC silicon-face dangling bonds

G. Pennington and C. R. Ashman

Appl. Phys. Lett. 91, 072106 (2007); http://dx.doi.org/10.1063/1.2770653 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2007

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The authors report a density functional theory study of nitrogen passivation of the (0001) Si face of 4H-SiC. Results indicate that (1) upon passivation dangling bond density is reduced near the conduction band and increased near the valence band and (2) stable nitrogen coverage is allowed only up to 1/3 of a monolayer. Although an oxygen environment is not considered, these findings concur with experimental studies of 4H-SiC metal-oxide-semiconductor field-effect transistors which have undergone gate oxide annealing in the presence of nitrogen. Simulations indicate that nitrogen may reduce interface state density by removing 4H-SiC Si-face dangling bonds.
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81.65.Rv Passivation
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states

In situ imaging of electromigration-induced nanogap formation by transmission electron microscopy

Hubert B. Heersche, Günther Lientschnig, Kevin O’Neill, Herre S. J. van der Zant, and Henny W. Zandbergen

Appl. Phys. Lett. 91, 072107 (2007); http://dx.doi.org/10.1063/1.2767149 (3 pages) | Cited 20 times

Online Publication Date: 17 August 2007

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The authors imaged electromigration-induced nanogap formation in situ by transmission electron microscopy. Real-time video recordings show that edge voids form near the cathode side. The polycrystalline gold wires narrow down until a single-grain boundary intersects the constriction along which the breaking continues. During the last 50 ms of the break, a relatively large deformation of the constriction’s geometry occurs. The shape of the anode (blunt) and the cathode (sharp) is asymmetric when the wire breaks with a bias voltage applied, but symmetric when a narrow constriction breaks spontaneously.
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66.30.Qa Electromigration
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries

Observation of type-I and type-II excitons in strained Si/SiGe quantum-well structures

K. Y. Wang, W. P. Huang, H. H. Cheng, G. Sun, R. A. Soref, R. J. Nicholas, and Y. W. Suen

Appl. Phys. Lett. 91, 072108 (2007); http://dx.doi.org/10.1063/1.2771094 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2007

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The authors report photoluminescence (PL) measurement on a series of Si/SiGe quantum-well structures that had different internal strain distributions. When each sample was placed in a high magnetic field, the field-dependent energy shift of the relevant PL peaks revealed either type-I or type-II exciton formation depending on the strain distribution. This observation is in agreement with theoretical modeling. The present investigation shows that type-I band alignment—desired for electroluminescent devices—can be achieved by strain engineering.
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78.55.Ap Elemental semiconductors
78.67.De Quantum wells
71.35.-y Excitons and related phenomena

Current transport mechanism of Au/Ni/GaN Schottky diodes at high temperatures

S. Huang, B. Shen, M. J. Wang, F. J. Xu, Y. Wang, H. Y. Yang, F. Lin, L. Lu, Z. P. Chen, Z. X. Qin, Z. J. Yang, and G. Y. Zhang

Appl. Phys. Lett. 91, 072109 (2007); http://dx.doi.org/10.1063/1.2772182 (3 pages) | Cited 14 times

Online Publication Date: 17 August 2007

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Current transport mechanism in Au/Ni/GaN Schottky diodes has been investigated using current-voltage characterization technique between 27 and 350 °C. It is found that the ideality factor n of the diode decreases with increasing temperature when the temperature is lower than 230 °C, and then increases with increasing temperature when the temperature is higher than 230 °C. The corresponding Schottky barrier height (SBH) increases all through the temperature range. Thermionic-emission model with a Gaussian distribution of SBHs is thought to be responsible for the electrical behavior at temperatures lower than 230 °C, while the generation-recombination (GR) process takes place in at temperatures above 230 °C. The effective Richardson constant is determined to be 24.08 A cm−2 K−2, in excellent agreement with the theoretical value. The extrapolated activation energy of the GR process is determined to be 1.157 eV. Based on the cathodoluminescence measurements, it is suggested that the deep level defects inducing yellow luminescence facilitate the GR process of the current transport in the diodes.
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85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions

Giant magnetoresistance in oxide-based metallic multilayers

Mara Granada, J. Carlos Rojas Sánchez, and Laura B. Steren

Appl. Phys. Lett. 91, 072110 (2007); http://dx.doi.org/10.1063/1.2772237 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2007

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The authors report on the first measurement of low-field giant magnetoresistance in metallic multilayers of perovskite oxides. The authors performed in-plane measurements of the magnetoelectric transport properties in La0.75Sr0.25MnO3/LaNiO3 trilayers and succeeded in distinguishing the giant magnetoresistance effect from other contributions to the total magnetoresistance. The samples were grown on single-crystalline SrTiO3 substrates by dc sputtering.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
81.15.Cd Deposition by sputtering
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