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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Proposal for an electrical spin cell with single barrier

B. H. Wu and Kang-Hun Ahn

Appl. Phys. Lett. 88, 142101 (2006); http://dx.doi.org/10.1063/1.2182069 (3 pages)

Online Publication Date: 3 April 2006

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We propose a spin cell based on photon-assisted tunneling through a conventional semiconductor barrier. The Dresselhaus spin-orbit interaction is included to break the spin rotation symmetry. Due to the in-plane electric field induced asymmetric momentum distribution in one lead, continuous flows of spin currents are driven through a barrier by an ac field. The net charge current remains zero. The spin current via photon-assisted tunneling can be readily adjusted via tuning the ac frequency or the in-plane electric field. This device may function as an ideal spin cell to supply spin currents in the spintronics circuit.
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72.25.-b Spin polarized transport
73.40.Gk Tunneling
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Analysis of graphene nanoribbons as a channel material for field-effect transistors

B. Obradovic, R. Kotlyar, F. Heinz, P. Matagne, T. Rakshit, M. D. Giles, M. A. Stettler, and D. E. Nikonov

Appl. Phys. Lett. 88, 142102 (2006); http://dx.doi.org/10.1063/1.2191420 (3 pages) | Cited 103 times

Online Publication Date: 3 April 2006

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Electronic properties of graphene (carbon) nanoribbons are studied and compared to those of carbon nanotubes. The nanoribbons are found to have qualitatively similar electron band structure which depends on chirality but with a significantly narrower band gap. The low- and high-field mobilities of the nanoribbons are evaluated and found to be higher than those of carbon nanotubes for the same unit cell but lower at matched band gap or carrier concentration. Due to the inverse relationship between mobility and band gap, it is concluded that graphene nanoribbons operated as field-effect transistors must have band gaps <0.5 eV to achieve mobilities significantly higher than those of silicon and thus may be better suited for low power applications.
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85.30.Tv Field effect devices
71.20.Tx Fullerenes and related materials; intercalation compounds
73.22.-f Electronic structure of nanoscale materials and related systems

On-chip photoconductive excitation and detection of pulsed terahertz radiation at cryogenic temperatures

C. Wood, J. Cunningham, P. C. Upadhya, E. H. Linfield, I. C. Hunter, A. G. Davies, and M. Missous

Appl. Phys. Lett. 88, 142103 (2006); http://dx.doi.org/10.1063/1.2191423 (3 pages) | Cited 4 times

Online Publication Date: 3 April 2006

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We report on measurements of the excitation, propagation, and detection of picosecond duration electrical pulses at cryogenic ( ∼ 4 K) temperatures in a microstrip circuit. A reduction is observed in the measured excitation and propagating pulse widths at low temperatures, compared with room temperature. The results indicate both that the electrical properties of low-temperature-grown GaAs make it suitable for photoconductive excitation and detection in cryogenic optoelectric circuits and that an organic polymer is a good transmissive medium for terahertz (THZ) frequency range excitations at low temperatures. This work will prove an invaluable starting point for future guided wave terahertz experiments at cryogenic temperatures.
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85.60.-q Optoelectronic devices
84.40.Dc Microwave circuits
84.40.Az Waveguides, transmission lines, striplines

Defects in silicon nanowires

R. P. Wang

Appl. Phys. Lett. 88, 142104 (2006); http://dx.doi.org/10.1063/1.2191830 (3 pages) | Cited 7 times

Online Publication Date: 4 April 2006

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Defects in silicon nanowires have been investigated using the electron spin resonance (ESR) method. The ESR signals consist of three features: a strong resonance at g = 2.002 49, a weak line at g = 2.000 48, and a broad feature at g = 2.005 41. From the saturation behavior and oxidation-related and temperature dependence analysis, we ascribe that the strong resonance corresponds to the EX center and the weak line to the well-assigned E′ center. We argue that the assignment of the broad feature to Pb centers [ A. Baumer et al., Appl. Phys. Lett. 85, 943 (2004) ] is oversimplified, and its physical origins may include dangling bonds in amorphous silicon.
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81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
71.55.Cn Elemental semiconductors
76.30.-v Electron paramagnetic resonance and relaxation
81.65.Mq Oxidation

Highly strain-relaxed ultrathin SiGe-on-insulator structure by Ge condensation process combined with H+ irradiation and postannealing

Masanobu Miyao, Masanori Tanaka, Isao Tsunoda, Taizoh Sadoh, Toyotsugu Enokida, Hiroyasu Hagino, Masaharu Ninomiya, and Masahiko Nakamae

Appl. Phys. Lett. 88, 142105 (2006); http://dx.doi.org/10.1063/1.2192644 (3 pages) | Cited 10 times

Online Publication Date: 4 April 2006

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Strain-relaxation process of SiGe-on-insulator (SGOI) structures in the oxidation induced Ge condensation method has been investigated as a function of the SiGe thickness. Complete relaxation was obtained for thick SGOI layers (>100 nm). However, the relaxation rates abruptly decreased with decreasing SiGe thickness below 50 nm, i.e., the relaxation rate of 30% at 30 nm SiGe thickness. In order to improve this phenomenon, a method combined with H+ irradiation with a medium dose (5×1015 cm−2) and postannealing (1200 °C) has been developed. This successfully achieved the high relaxation rate (70%) in the ultrathin SGOI (30 nm).
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81.05.Hd Other semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Quantitative mobility spectrum analysis of AlGaN/GaN heterostructures using variable-field hall measurements

N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, H. Morkoç, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 88, 142106 (2006); http://dx.doi.org/10.1063/1.2195011 (3 pages) | Cited 8 times

Online Publication Date: 5 April 2006

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Carrier transport properties of AlGaN/GaN heterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally undoped Al0.08Ga0.92N/GaN sample was grown by plasma-assisted molecular beam epitaxy on a GaN/sapphire template prepared with hydride vapor phase epitaxy. Variable-magnetic-field Hall measurements were carried out in the temperature range of 5–300 K and magnetic field range of 0.01–7 T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility two-dimensional electron gas and the relatively low-mobility bulk electrons for the temperature range investigated. The mobilities at T = 80 K are found to be 7100 and 880 cm2/V s, respectively, while the corresponding carrier densities are 7.0×1011 and 8×1014 cm−3. Any conclusions drawn from conventional Hall measurements at a single magnetic field would have been highly misleading.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

InGaAs dual channel transistors with negative differential resistance

Takeyoshi Sugaya, Kazuhiro Komori, Takashi Yamane, Souichirou Hori, and Kenji Yonei

Appl. Phys. Lett. 88, 142107 (2006); http://dx.doi.org/10.1063/1.2193728 (3 pages) | Cited 3 times

Online Publication Date: 5 April 2006

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We demonstrate InGaAs dual channel transistors (DCTs) with negative differential resistance (NDR) fabricated on an InP (001) substrate. The dual channel structure consists of high and low mobility InGaAs quantum wells combined with an InAlAs barrier layer. NDR characteristics of the DCTs depend on the thicknesses of the low mobility and barrier layers and the indium content of the high mobility channel. The NDR mechanism is thought to be the carrier transfer from the high mobility channel to the low mobility channel.
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85.30.Pq Bipolar transistors
73.21.Fg Quantum wells
73.63.Hs Quantum wells
72.20.Fr Low-field transport and mobility; piezoresistance

Fabrication of silicon-on-SiO2/diamondlike-carbon dual insulator using ion cutting and mitigation of self-heating effects

Zengfeng Di, Paul K. Chu, Ming Zhu, Ricky K. Y. Fu, Suhua Luo, Lin Shao, M. Nastasi, Peng Chen, T. L. Alford, J. W. Mayer, Miao Zhang, Weili Liu, Zhitang Song, and Chenglu Lin

Appl. Phys. Lett. 88, 142108 (2006); http://dx.doi.org/10.1063/1.2192981 (3 pages) | Cited 3 times

Online Publication Date: 5 April 2006

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A diamondlike-carbon (DLC) layer was used to substitute for the buried SiO2 layer in silicon on insulator (SOI) to mitigate the self-heating effects in our previous study. However, we discovered drawbacks associated with the inferior Si/DLC interface, inadequate thermal stability as well as carbon-silicon interdiffusion at the Si/DLC interface that could hamper future application of this silicon-on-diamond structure to microelectronic devices. In this work, we introduced a silicon dioxide barrier layer between the Si film and DLC buried layer to form a silicon-on-SiO2/DLC dual-insulator structure to tackle these problems. Cross-sectional high-resolution transmission electron microscopy reveals that the Si/insulator interface is atomically flat and the top Si layer has nearly perfect crystalline quality. The SiO2/DLC dual-insulator layer retains excellent insulating properties at typical complementary metal oxide silicon processing temperatures. Numerical simulation reveals that the negative differential resistance and channel temperature are significantly reduced compared with those of the same metal oxide semiconductor field effect transistors fabricated in conventional SiO2-based SOI, suggesting that the silicon-on-dual-insulator structure can alleviate the self-heating penalty effectively.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.60.Dv Thermal stability; thermal effects

Electrical properties of n-type GaPN grown by molecular-beam epitaxy

Yuzo Furukawa, Hiroo Yonezu, Akihiro Wakahara, Yusuke Yoshizumi, Yoshiro Morita, and Atsushi Sato

Appl. Phys. Lett. 88, 142109 (2006); http://dx.doi.org/10.1063/1.2193350 (3 pages) | Cited 4 times

Online Publication Date: 6 April 2006

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We have investigated electrical properties of n-GaPN layers grown by molecular-beam epitaxy with an rf-plasma source using sulfur and tellurium as dopants. The electron concentration in n-GaPN was about 10 times lower than that in n-GaP. Desorption of dopants from the grown surface by impinging N atoms may be one of the possible causes for the reduced electron concentration. In addition, electron mobilities in GaPN were restricted by ionized impurity scattering even at room temperature (RT). N atoms at N-related levels could trap the electrons, and these ionized N could act as a Columb scattering center for free electrons even at RT.
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73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.77.Dq Plasma-based ion implantation and deposition
61.72.uj III-V and II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

Thermionic emission perpendicular to bulk and multiquantum AlxGa1−xInP barriers

J. Ní Chróinín and A. P. Morrison

Appl. Phys. Lett. 88, 142110 (2006); http://dx.doi.org/10.1063/1.2181648 (3 pages)

Online Publication Date: 7 April 2006

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A study on thermally activated currents across the bulk and multiquantum barrier (MQB) AlxGa1−xInP/GaInP has been carried out and compared to experimental results from a series of n-i-n diodes over a range of temperatures. By considering the true quantum mechanical nature of the barriers, in contrast to the classical Richardson formalism, it is found that the alloy crossover strongly affects the transport properties of the material. The measured prefactor is found to decrease as Al content is increased. When applied to the MQB structures, the existing model fails to capture the experimental results.
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79.40.+z Thermionic emission
85.30.Kk Junction diodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Rectifying NdNiO3/Nb:SrTiO3 junctions as a probe of the surface electronic structure of NdNiO3

Y. Kozuka, T. Susaki, and H. Y. Hwang

Appl. Phys. Lett. 88, 142111 (2006); http://dx.doi.org/10.1063/1.2193800 (3 pages) | Cited 12 times

Online Publication Date: 7 April 2006

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We have studied the electronic properties of junctions formed between Nb-doped SrTiO3 substrates, an n-type semiconductor, and NdNiO3 films, which exhibit a strong first-order phase transition from a high temperature paramagnetic metal to a low temperature antiferromagnetic insulator. Although the junctions are rectifying at all temperatures, the current-voltage and capacitance characteristics show no indication of the metal-insulator transition clearly observed in the films. This suggests that the surface electronic structure of NdNiO3 is distinct from the interior of the film and does not undergo the bulk transition.
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73.40.Ei Rectification
73.20.At Surface states, band structure, electron density of states
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Hydrogen self-trapping near silicon atoms in Ge-rich SiGe alloys

R. N. Pereira, B. Bech Nielsen, J. Coutinho, V. J. B. Torres, and P. R. Briddon

Appl. Phys. Lett. 88, 142112 (2006); http://dx.doi.org/10.1063/1.2193802 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2006

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Infrared absorption spectroscopy and ab initio density functional modeling are used to investigate hydrogen defects that are stable at and above room temperature in proton-implanted Ge-rich SiGe alloys. We find that Si atoms are effective nucleation sites for hydrogen, leading to the formation of a dominant defect closely related to the H2* dimer in pure Si and Ge. The minority Si species in the alloys stabilizes the new complex, and strongly reduces the trapping efficiency of hydrogen by vacancies and self-interstitials.
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71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
78.30.Hv Other nonmetallic inorganics

Evaluation of titanium silicon nitride as gate electrodes for complementary metal-oxide semiconductor

H. Luan, H. N. Alshareef, H. R. Harris, H. C. Wen, K. Choi, Y. Senzaki, P. Majhi, and B.- H. Lee

Appl. Phys. Lett. 88, 142113 (2006); http://dx.doi.org/10.1063/1.2188380 (3 pages) | Cited 4 times

Online Publication Date: 7 April 2006

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The effect of deposition temperature and film thickness on the work function of TiSiN gate electrodes has been studied. It is shown that the work function of TiSiN can be tuned from 4.28–4.74 eV on SiO2, 4.40–4.79 eV on HfO2, and 4.44–4.83 eV on HfSiOx. For high-k dielectrics, the work function can be tuned by 200 meV on each side of the band gap, making it a suitable electrode for fully depleted silicon-on-insulator devices. Furthermore, TiSiN deposition at high temperature increases the work function to 4.87 eV while Si implantation increases it to 4.93 eV, making TiSiN a good p-type metal candidate.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
71.20.-b Electron density of states and band structure of crystalline solids
77.55.-g Dielectric thin films
85.30.Tv Field effect devices

Robust, scalable self-aligned platinum silicide process

Z. Zhang, S.-L. Zhang, M. Östling, and J. Lu

Appl. Phys. Lett. 88, 142114 (2006); http://dx.doi.org/10.1063/1.2194313 (3 pages) | Cited 5 times

Online Publication Date: 7 April 2006

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A robust, scalable PtSix process is developed. The process consists of two consecutive annealing steps in a single run; the first is silicidation of Pt films on Si substrates carried out in N2, whereas the second is surface oxidation of the resultant PtSix in O2. By adequately adjusting the temperature during the oxidation step, a protective SiOx hard mask forms on PtSix of different thicknesses and compositions. Such a surface oxidation is absent for Pt on SiO2 isolation, which is crucial for the subsequent selective wet etch for a self-aligned process. Ultralong PtSix nanowires are fabricated using this robust self-aligned process.
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68.65.La Quantum wires (patterned in quantum wells)
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Band offsets in the Sc2O3/GaN heterojunction system

J.-J. Chen, B. P. Gila, M. Hlad, A. Gerger, F. Ren, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 88, 142115 (2006); http://dx.doi.org/10.1063/1.2194314 (3 pages) | Cited 9 times

Online Publication Date: 7 April 2006

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The Sc2O3/GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN/GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3/GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv = 0.42±0.07 eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0 eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14 eV in this system.
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71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
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