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17 Aug 2009

Volume 95, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 95, 073703 (2009); http://dx.doi.org/10.1063/1.3152768 (3 pages)

Mohammud R. Noor, Swati Goyal, Shawn M. Christensen, and Samir M. Iqbal
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Strong nonlinear optical response of graphene in the terahertz regime

A. R. Wright, X. G. Xu, J. C. Cao, and C. Zhang

Appl. Phys. Lett. 95, 072101 (2009); http://dx.doi.org/10.1063/1.3205115 (3 pages) | Cited 24 times

Online Publication Date: 17 August 2009

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We demonstrate that within the model of massless Dirac fermions, graphene has a strong nonlinear optical response in the terahertz regime. It is found that the nonlinear contribution significantly alters both the single frequency and frequency tripled optical response at experimentally relevant field strengths. The optical activity of single layer graphene is significantly enhanced by nonlinear effects, and the frequency tripled response opens the gateway to photonic and optoelectronic device applications.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Observation of negative differential transconductance in tunneling emitter bipolar transistors

Marc J. van Veenhuizen, Nicolas Locatelli, Jagadeesh Moodera, and Joonyeon Chang

Appl. Phys. Lett. 95, 072102 (2009); http://dx.doi.org/10.1063/1.3205104 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2009

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We report on measurement of negative differential transconductance (NDTC) of iron (Fe)/magnesium-oxide (MgO)/silicon tunneling emitter NPN bipolar transistors. Device simulations reveal that the NDTC is a consequence of an inversion layer at the tunneling-oxide/P-silicon interface for low base voltages. Electrons travel laterally through the inversion layer into the base and give rise to an increase in collector current. The NDTC results from the recombination of those electrons at the interface between emitter and base contact which is dependent on the base voltage. For larger base voltages, the inversion layer disappears marking the onset of normal bipolar transistor behavior.
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85.30.Pq Bipolar transistors

Experimental validation of a higher dimensional theory of electrical contact resistance

Matthew R. Gomez, David M. French, Wilkin Tang, Peng Zhang, Y. Y. Lau, and R. M. Gilgenbach

Appl. Phys. Lett. 95, 072103 (2009); http://dx.doi.org/10.1063/1.3205116 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2009

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The increased resistance of a cylindrical conducting channel due to constrictions of various radii and axial lengths was measured experimentally. The experimental data corroborate the higher dimensional contact resistance theory that was recently developed.
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73.40.Cg Contact resistance, contact potential

High performance thin film transistor with cosputtered amorphous Zn–In–Sn–O channel: Combinatorial approach

Min Ki Ryu, Shinhyuk Yang, Sang-Hee Ko Park, Chi-Sun Hwang, and Jae Kyeong Jeong

Appl. Phys. Lett. 95, 072104 (2009); http://dx.doi.org/10.1063/1.3206948 (3 pages) | Cited 26 times

Online Publication Date: 18 August 2009

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Thin film transistors with a channel of Zn–In–Sn–O were fabricated via a combinatorial rf sputtering method. It was found that the role of the In atoms is to enhance the mobility and to shift the threshold voltage (Vth) negatively. On the other hand, the Sn fraction is critical for improving the overall trap density including the density-of-states of the bulk channel layer and the interfacial trap density at the ZnInSnO interface. The optimized transistor was obtained at a compositional ratio of Zn:In:Sn = 40:20:40, which exhibited an excellent subthreshold gate swing of 0.12 V/decade, Vth of −0.4 V, and high Ion/off ratio of >109 as well as a high field-effect mobility of 24.6 cm2/V s.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

The polarity origin of the bipolar resistance switching behaviors in metal/La0.7Ca0.3MnO3/Pt junctions

R. Yang, X. M. Li, W. D. Yu, X. D. Gao, D. S. Shang, X. J. Liu, X. Cao, Q. Wang, and L. D. Chen

Appl. Phys. Lett. 95, 072105 (2009); http://dx.doi.org/10.1063/1.3203999 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2009

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Bipolar resistance switching behaviors in the M/La0.7Ca0.3MnO3/Pt (M = Pt, Ag, Cu, Al, Ti, and W) junctions were investigated. We found that the switching polarities of the junctions for M = Pt, Ag, and Cu were opposite to those for M = Al, Ti, and W. This phenomenon was attributed to the different Gibbs free energy of the metal oxide formation. Based on Auger electron spectroscopy measurement of the M/La0.7Ca0.3MnO3 interfaces, the switching mechanisms were further discussed in terms of metal electrode redox reaction for M = Al, Ti, and W and oxygen vacancy generation/annihilation in the La0.7Ca0.3MnO3 film for M = Pt, Ag, and Cu, respectively.
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73.40.Rw Metal-insulator-metal structures
79.20.Fv Electron impact: Auger emission
82.45.Fk Electrodes
61.72.jd Vacancies

Terahertz radiation detection by field effect transistor in magnetic field

S. Boubanga-Tombet, M. Sakowicz, D. Coquillat, F. Teppe, W. Knap, M. I. Dyakonov, K. Karpierz, J. Łusakowski, and M. Grynberg

Appl. Phys. Lett. 95, 072106 (2009); http://dx.doi.org/10.1063/1.3207886 (3 pages) | Cited 5 times

Online Publication Date: 19 August 2009

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We report on terahertz radiation detection with InGaAs/InAlAs field effect transistors in quantizing magnetic field. The photovoltaic detection signal was investigated as a function of the gate voltage and magnetic field. Oscillations analogous to Shubnikov–de Haas oscillations as well as their strong enhancement at the cyclotron resonance were observed. The results are quantitatively described by a recent theory, showing that the detection is due to rectification of the terahertz radiation by plasma waves related nonlinearities in the gated part of the channel.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.Tv Field effect devices

Origin of nanoscale potential fluctuations in two-dimensional semiconductors

S. Landrock, Y. Jiang, K. H. Wu, E. G. Wang, K. Urban, and Ph. Ebert

Appl. Phys. Lett. 95, 072107 (2009); http://dx.doi.org/10.1063/1.3177329 (3 pages) | Cited 9 times

Online Publication Date: 19 August 2009

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We demonstrate a direct atomically resolved visualization and quantification of the impact of inhomogeneities in the dopant distribution on the nanoscale potential fluctuations in a two-dimensional semiconducting math×math Ga overlayer on Si(111) using scanning tunneling microscopy. By a quantitative analysis, two regimes of the potential at nanometer scale are found, which arise from the local distribution of charge carriers in the bands and from electron-electron interactions.
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81.05.Cy Elemental semiconductors
72.20.Dp General theory, scattering mechanisms
73.61.Cw Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.A- Nucleation and growth
68.55.ag Semiconductors

Nanoscale doping of InAs via sulfur monolayers

Johnny C. Ho, Alexandra C. Ford, Yu-Lun Chueh, Paul W. Leu, Onur Ergen, Kuniharu Takei, Gregory Smith, Prashant Majhi, Joseph Bennett, and Ali Javey

Appl. Phys. Lett. 95, 072108 (2009); http://dx.doi.org/10.1063/1.3205113 (3 pages) | Cited 14 times

Online Publication Date: 20 August 2009

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One of the challenges for the nanoscale device fabrication of III-V semiconductors is controllable postdeposition doping techniques to create ultrashallow junctions. Here, we demonstrate nanoscale, sulfur doping of InAs planar substrates with high dopant areal dose and uniformity by using a self-limiting monolayer doping approach. From transmission electron microscopy and secondary ion mass spectrometry, a dopant profile abruptness of ∼ 3.5 nm/decade is observed without significant defect density. The n+/p+ junctions fabricated by using this doping scheme exhibit negative differential resistance characteristics, further demonstrating the utility of this approach for device fabrication with high electrically active sulfur concentrations of ∼ 8×1018 cm−3.
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61.72.uj III-V and II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Compensation of interfacial states located inside the “buffer-free” GaSb/GaAs (001) heterojunction via δ-doping

A. Jallipalli, K. Nunna, M. N. Kutty, G. Balakrishnan, G. B. Lush, L. R. Dawson, and D. L. Huffaker

Appl. Phys. Lett. 95, 072109 (2009); http://dx.doi.org/10.1063/1.3210783 (3 pages) | Cited 2 times

Online Publication Date: 20 August 2009

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We report the compensation of interfacial states formed by interfacial misfit dislocation (IMF) arrays via δ-doping. The IMF arrays are located inside the “buffer-free” heterojunction of GaSb/GaAs (001). The interfacial states are measured using surface photovoltage measurements and are positioned at 0.41, 0.49, and 0.61 eV. A higher reverse bias leakage current (IRB) was observed in the heterogeneous GaSb/GaAs IMF sample (73 μA at −5 V) compared to the homogeneous GaAs control sample (3.9 μA), which does not contain IMF. This increase in IRB is attributed to the interfacial states. Hence, the interfacial states are compensated by δ-doping the GaSb/GaAs interface using Te atoms. A low turn-on voltage of 0.85 V and a very low IRB of 0.1 nA were achieved for the δ-doped sample compared to the control and IMF samples. Hence, for optoelectronic applications, such as lasers, solar cells, and detectors, this compensated IMF technology is useful for integration of buffer-free III-Sb devices on an inexpensive GaAs platform.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors

Current-induced spin polarization in gallium nitride

W. F. Koehl, M. H. Wong, C. Poblenz, B. Swenson, U. K. Mishra, J. S. Speck, and D. D. Awschalom

Appl. Phys. Lett. 95, 072110 (2009); http://dx.doi.org/10.1063/1.3194781 (3 pages) | Cited 5 times

Online Publication Date: 20 August 2009

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Electrically generated spin polarization is probed directly in bulk GaN using Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the wurtzite phase both by molecular beam epitaxy and metalorganic chemical vapor deposition with a variety of doping densities chosen to broadly modulate the transverse spin lifetime, T2∗. The spin polarization is characterized as a function of electrical excitation energy over a range of temperatures. Despite weak spin-orbit interactions in GaN, a current-induced spin polarization is observed in the material at temperatures of up to 200 K.
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73.61.Ey III-V semiconductors
72.25.Dc Spin polarized transport in semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ek Optical activity

Correlation between a threshold failure time and void nucleation for describing the bimodal electromigration behavior of copper interconnects

R. G. Filippi, P.-C. Wang, A. Brendler, and J. R. Lloyd

Appl. Phys. Lett. 95, 072111 (2009); http://dx.doi.org/10.1063/1.3200233 (3 pages) | Cited 3 times

Online Publication Date: 21 August 2009

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Electromigration testing of an interconnect system comprised of copper metallization and a low-k dielectric material gives rise to bimodal lognormal statistics with early and late fails. When separated from one another, we observed failure modes characterized by a three-parameter lognormal distribution and the same threshold failure time. It is shown that the threshold failure time corresponds to damage (presumably voids) nucleation of the electromigration process. The dependence of the threshold failure time and the median time to failure on current density suggests that both void nucleation and void growth need to be considered for accurate modeling of the electromigration lifetime.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
02.50.Ng Distribution theory and Monte Carlo studies

High performance ZnO-thin-film transistor with Ta2O5 dielectrics fabricated at room temperature

L. Zhang, J. Li, X. W. Zhang, X. Y. Jiang, and Z. L. Zhang

Appl. Phys. Lett. 95, 072112 (2009); http://dx.doi.org/10.1063/1.3206917 (3 pages) | Cited 21 times

Online Publication Date: 21 August 2009

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The authors report on the fabrication of low-driven-voltage and high mobility ZnO thin-film transistor with sputtering Ta2O5 film as the dielectric. The device shows a field effect mobility of 60.4 cm2/V s, a threshold voltage of 1.1 V, an on/off ratio of 1.22×107, and a subthreshold swing of 0.23 V/decade. The high mobility partially resulted from the fringing-electric-field effect due to the undefined active layer. Therefore, considering our device geometry, the actual mobility is about 40.5 cm2/V s. We contribute the high performance to the proper dielectric thickness, smooth insulator surface, and relatively low trap state densities in the insulator/channel interface.
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85.30.Tv Field effect devices
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