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13 Feb 2006

Volume 88, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 88, 072905 (2006); http://dx.doi.org/10.1063/1.2172744 (3 pages)

Y. L. Li and L. Q. Chen
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Low-voltage and high-field-effect mobility organic transistors with a polymer insulator

Yunseok Jang, Do Hwan Kim, Yeong Don Park, Jeong Ho Cho, Minkyu Hwang, and Kilwon Cho

Appl. Phys. Lett. 88, 072101 (2006); http://dx.doi.org/10.1063/1.2173633 (3 pages) | Cited 55 times

Online Publication Date: 13 February 2006

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A key issue in research into organic thin-film transistors (OTFTs) is low-voltage operation. In this study, we fabricated a pentacene thin-film transistor with an ultrathin layer of polyvinyl alcohol (9 nm) as a gate insulator, and obtained a device with excellent electrical characteristics at low operating voltages (below 2 V). This device was found to have a field-effect mobility of 1.1 cm2/V s, a threshold voltage of −0.98 V, an exceptionally low subthreshold slope of 180 mV/decade, and an on/off current ratio of 106. This favorable combination of properties means that such OTFTs can be operated successfully at voltages below 2 V.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Current crowding-induced electromigration in SnAg3.0Cu0.5 microbumps

Kuo Ning Chiang, Chien Chen Lee, Chang Chun Lee, and Kuo Ming Chen

Appl. Phys. Lett. 88, 072102 (2006); http://dx.doi.org/10.1063/1.2173710 (3 pages) | Cited 18 times

Online Publication Date: 13 February 2006

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To determine the relevance of current crowding to electromigration in the SnAg3.0Cu0.5 solder bump, a three-dimensional dual bumps simulation model was designed to demonstrate how current crowding can enhance the local atomic flux along the electron flow path. The finding of void formation occurred at the entrance points to the cathode sides and the enhancement of the growth and clustering of the intermetallic compound at the outgoing points of the anode sides along the electron flow path were verified experimentally. The tilting effect is obvious at the anode/chip side. The experimental mean-time-to-failure was observed, and Black’s equation with Joule heating effect were investigated as well.
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66.30.Qa Electromigration
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Fabrication and characterization of vertical-type double-gate metal-oxide-semiconductor field-effect transistor with ultrathin Si channel and self-aligned source and drain

Meishoku Masahara, Yongxun Liu, Kazuhiko Endo, Takashi Matsukawa, Kunihiro Sakamoto, Kenichi Ishii, Shinichi O’uchi, Etsuro Sugimata, Hiromi Yamauchi, and Eiichi Suzuki

Appl. Phys. Lett. 88, 072103 (2006); http://dx.doi.org/10.1063/1.2173715 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2006

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A fabrication technique for a vertical double-gate metal-oxide-semiconductor field-effect transistor (DG MOSFET) with a standing-up ultrathin channel (UTC) and self-aligned source and drain (S/D) is proposed. A 20 nm thick vertical UTC with low channel thickness fluctuation was formed on a (110)-oriented Si substrate using orientation-dependent wet etching. The top and bottom S/D were self-aligned to the DGs by using a combination of ion implantation and solid-phase diffusion. The fabricated vertical DG MOSFETs revealed that the channel thickness less influences the threshold voltage. Furthermore, a low sub-threshold slope of 68.8 mV/decade was achieved with a channel thickness of 20 nm.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning

Metalorganic chemical vapor deposition growth of high-quality InAs/GaSb type II superlattices on (001) GaAs substrates

X. B. Zhang, J. H. Ryou, R. D. Dupuis, A. Petschke, S. Mou, S. L. Chuang, C. Xu, and K. C. Hsieh

Appl. Phys. Lett. 88, 072104 (2006); http://dx.doi.org/10.1063/1.2168668 (3 pages) | Cited 12 times

Online Publication Date: 14 February 2006

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InAs layers and InAs/GaSb type II superlattices (SLs) were grown on (001) GaAs substrates by metalorganic chemical vapor deposition. A thin low-temperature GaSb nucleation layer and a thicker high-temperature metamorphic GaSb buffer layer were introduced before the growth of InAs or the SLs. By optimizing the growth temperature, the interface gas switching and the growth rate, morphology, and structural properties of the grown structures are significantly improved. In some cases, nanopipes are found in these structures. Morphology studies of the InAs heteroepitaxial layers show that (1) the diameter of these nanopipes decreases with the growth temperature; (2) nanopipes are nucleated from the interface of GaSb/InAs; and (3) the density of nanopipes depends on the passivation of GaSb surface before the growth of the InAs. In growing InAs/GaSb SLs, we show that the growth rate of GaSb has a strong effect on the morphology and that the unintentional interfacial InSb layer formed at the InAs/GaSb interfaces is the origin of the nanopipes. Through the optimization of the growth parameters, high-quality 100-period SLs without nanopipes and with good optical absorption in 3–8 μm infrared region have been realized.
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81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation
78.30.Fs III-V and II-VI semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

High-field magnetoresistance in p-(In,Mn)As/n-InAs heterojunctions

S. J. May and B. W. Wessels

Appl. Phys. Lett. 88, 072105 (2006); http://dx.doi.org/10.1063/1.2174108 (3 pages) | Cited 9 times

Online Publication Date: 15 February 2006

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The high-field magnetoresistive properties of a p-In0.96Mn0.04As/n-InAs junction have been measured. The heterojunction was formed by epitaxially depositing an InMnAs thin film on an InAs substrate using metalorganic vapor phase epitaxy. Under forward bias, a large nonsaturating magnetoresistance is observed at temperatures from 25 to 295 K in fields up to 9 T. At room temperature, the magnetoresistance increases linearly with magnetic field from 1.5 to 9 T and is greater than 700% at 9 T. The magnetoresistance can be simulated using a modified diode equation, including a field-dependent series magnetoresistance.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
75.47.Pq Other materials

Electric-field effects on persistent photoconductivity in undoped n-type epitaxial GaN

Jintong Xu, Da You, Yingwen Tang, Yong Kang, Xue Li, Xiangyang Li, and Haimei Gong

Appl. Phys. Lett. 88, 072106 (2006); http://dx.doi.org/10.1063/1.2174841 (3 pages) | Cited 3 times

Online Publication Date: 15 February 2006

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Investigations of electric-field effects on persistent photoconductivity (PPC) in undoped n-type epitaxial GaN are presented. We have observed that, by applying a high-voltage pulse, the course of PPC was effectively accelerated. Moreover, the current relative responsivity changed with biases across the GaN region, which was not seen in normal photoconductivity phenomena. Experiments were also conducted to indicate notable differences between heating effects and electric-field effects on PPC decay course. Our results show that field-associated changes in trapping parameters are responsible for the above abnormal phenomena.
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72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

Ordering of high-quality InAs quantum dots on defect-free nanoholes

Jong Su Kim, Mitsuo Kawabe, and Nobuyuki Koguchi

Appl. Phys. Lett. 88, 072107 (2006); http://dx.doi.org/10.1063/1.2174097 (3 pages) | Cited 18 times

Online Publication Date: 16 February 2006

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We demonstrate a promising way for the fabrication of high-quality InAs quantum dot (QD) arrays by combining atomic force microscope (AFM) tip-induced nano-oxidation, atomic-hydrogen etching/cleaning (AHE/C), and droplet epitaxy method. The highly aligned defect-free nanoholes as nucleation sites were fabricated by using AFM tip-induced nano-oxidation and subsequent AHE/C. Using the droplet epitaxy on the artificially patterned nanoholes, we fabricated laterally arrayed InAs QDs with an interdot distance of 100 nm. The photoluminescence from the InAs QD arrays showed strong emission at 1.22 eV, even though the processed interface directly faced the base of the InAs QDs, indicating that the process can reduce the physical and chemical defects/contaminants at the nanoholes and interface.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
81.65.Cf Surface cleaning, etching, patterning
78.67.Hc Quantum dots

Composition dependence of the work function of Ta1−xAlxNy metal gates

H. N. Alshareef, K. Choi, H. C. Wen, H. Luan, H. Harris, Y. Senzaki, P. Majhi, B. H. Lee, R. Jammy, S. Aguirre-Tostado, B. E. Gnade, and R. M. Wallace

Appl. Phys. Lett. 88, 072108 (2006); http://dx.doi.org/10.1063/1.2174836 (3 pages) | Cited 12 times

Online Publication Date: 16 February 2006

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It is shown that the work function of Ta1−xAlxNy depends on the electrode and gate dielectric compositions. Specifically, the work function of Ta1−xAlxNy increased with SiO2 content in the gate dielectric, reaching as high as 5.0 eV on SiO2; the work function was nearly 400 mV smaller on HfO2. In addition, the work function decreased with increasing nitrogen content in the Ta1−xAlxNy metal gate. Increasing Al concentration increased the work function up to about 15% Al, but the work function decreased for higher Al concentrations. Chemical analysis shows that Al–O bonding at the interface correlates with the observed work function values.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Effects of polymer gate dielectrics roughness on pentacene field-effect transistors

Kwonwoo Shin, Chanwoo Yang, Sang Yoon Yang, Hayoung Jeon, and Chan Eon Park

Appl. Phys. Lett. 88, 072109 (2006); http://dx.doi.org/10.1063/1.2176858 (3 pages) | Cited 28 times

Online Publication Date: 17 February 2006

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The effects of the surface roughness of the polymer gate dielectrics on pentacene field-effect transistors were investigated. Using a poly(methylmethacrylate)/anodized Al2O3 dual-layer gate dielectric, the root-mean-square roughness of the gate dielectrics varied from 0.45 to 1.51 nm, independently of other gate dielectric properties such as the capacitance and surface energy. This range of root-mean-square roughnesses had little effect on the carrier mobility. X-ray diffraction analyses further revealed that the roughness of poly(methylmethacrylate) neither decreased the degree of crystallinity nor distorted the crystalline structure of pentacene.
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85.30.Tv Field effect devices
77.84.Jd Polymers; organic compounds

Nonlinear current-voltage characteristics of bismuth nanodot structures

Pit Ho Patrio Chiu and Ishiang Shih

Appl. Phys. Lett. 88, 072110 (2006); http://dx.doi.org/10.1063/1.2177539 (3 pages) | Cited 3 times

Online Publication Date: 17 February 2006

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Bismuth (Bi) nanodot structures have been fabricated using the proximity effects of electron-beam writing technique. Bi nanodots, each 100 nm in diameter, were fabricated on an oxidized silicon substrate with a 200 nm thick silicon oxide layer. Current-voltage (I-V) measurements were performed under low vacuum condition at temperatures from 77 to 300 K. The measurement results showed significant nonlinearities with symmetric resistance peaks, indicating the existence of energy level spacing within the nanodot structures. The successful observation of energy level spacing in such a large nanodot is due to the small effective mass of Bi material, which leads to measurable energy level spacing.
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73.63.-b Electronic transport in nanoscale materials and structures
73.63.Kv Quantum dots

Electronic conduction in GaN nanowires

B. S. Simpkins, P. E. Pehrsson, and A. R. Laracuente

Appl. Phys. Lett. 88, 072111 (2006); http://dx.doi.org/10.1063/1.2177629 (3 pages) | Cited 11 times

Online Publication Date: 17 February 2006

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Conductivity mechanisms in unintentionally doped GaN nanowires (NWs) are studied. Gated current-voltage measurements and threshold voltage modeling demonstrate the unique impact of device parameters on NW field-effect transistors as compared to conventional systems. Temperature-dependent resistivity results, acquired with a scanning tunneling microscope equipped with multiple tips, reveal only mild temperature dependence at higher temperatures, with temperature-independent resistivity observed below ∼ 100 K indicating impurity band conduction. The likely origins and implications of these results are discussed.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
71.55.Eq III-V semiconductors
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