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15 Oct 2007

Volume 102, Issue 8, Articles (08xxxx)

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J. Appl. Phys. 102, 081301 (2007); http://dx.doi.org/10.1063/1.2799091 (28 pages)

V. V. Afanas’ev and A. Stesmans
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Hole mobility in silicon inversion layers: Stress and surface orientation

Guangyu Sun, Yongke Sun, Toshikazu Nishida, and Scott E. Thompson

J. Appl. Phys. 102, 084501 (2007); http://dx.doi.org/10.1063/1.2795649 (7 pages) | Cited 27 times

Online Publication Date: 18 October 2007

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Hole transport in the p-type metal-oxide-semiconductor field-effect-transistor (p-MOSFET) inversion layer under arbitrary stress, surface, and channel orientation is investigated by employing a six-band k∙p model and finite difference formalism. The piezoresistance coefficients are calculated and measured at stresses up to 300 MPa via wafer-bending experiments for stresses of technological importance: uniaxial and biaxial stresses on (001) and (110) surface oriented p-MOSFETs with ⟨110⟩ and ⟨111⟩ channels. With good agreement in the measured and calculated small stress piezoresistance coefficients, k∙p calculations are used to give physical insights into hole mobility enhancement at large stress ( ∼ 3 GPa). The results show that the maximum hole mobility is similar for (001)/〈110〉, (110)/〈110〉, and (110)/〈111〉 p-MOSFETs under uniaxial stress, although the enhancement factor is different. Strong quantum confinement and a low density of states cause less stress-induced mobility enhancement for (110) p-MOSFETs. For (001) p-MOSFETs, the dominant factor for the improved hole mobility is reduced conductivity effective mass at small stress and lower phonon scattering rate at large stress.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Realization of dot- and antidot-type two-dimensional photonic crystals by double holographic method

Jong-Bin Yeo, Sang-Don Yun, and Hyun-Yong Lee

J. Appl. Phys. 102, 084502 (2007); http://dx.doi.org/10.1063/1.2799077 (5 pages) | Cited 5 times

Online Publication Date: 18 October 2007

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Two-dimensional photonic crystals (2D PCs) were fabricated on a 1.18-μm-thick polymer resist (DMI-150) by a double-exposure holographic method using a HeCd laser with a wavelength of 442 nm. The 2D PC arrays exhibited various primitive lattice structures from triangle to square according to the change of the rotation angle (γ) of the double-exposure beams. In addition, the period, filling factor, and form (dot or antidot) of the PCs could be controlled by the experimental conditions such as the incident interference angle (θ), the exposure power, and duration. The following exposure procedure was applied: first holographic exposure, followed by sample rotation, and finally, second holographic exposure. The first and second holographic exposures were carried out at a fixed angle (θ = 11°) and the rotation was performed in the range of γ = 45°–90°. The variation of diffraction efficiency (η) during the exposure process and after the development was monitored using a HeNe laser in real time. The images of the prepared 2D PCs were observed by scanning electron microscopy and atomic force microscopy, and the data on their reciprocal lattices were obtained by the diffracted patterns. We believe that the double holographic method is a suitable tool to realize the dot- and antidot-type 2D PCs with a periodic array of a large area.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Jk Polymers and organics
42.40.My Applications
42.62.Cf Industrial applications
42.70.Qs Photonic bandgap materials

Light output improvement of InGaN ultraviolet light-emitting diodes by using wet-etched stripe-patterned sapphire substrates

Chang-Chi Pan, Chi-Hsun Hsieh, Chih-Wei Lin, and Jen-Inn Chyi

J. Appl. Phys. 102, 084503 (2007); http://dx.doi.org/10.1063/1.2798537 (5 pages) | Cited 10 times

Online Publication Date: 19 October 2007

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GaN-based epilayers are grown on wet-etched stripe-patterned sapphire substrates, with stripes along the 〈11−20〉sapphire and 〈1−100〉sapphire directions, for 400 nm ultraviolet light-emitting diodes (LEDs). The effects of the etching depth and stripe orientation on the structural and optical properties of the GaN layer as well as on the LEDs are investigated. Much better material quality and light output power are obtained when the GaN and the LEDs are grown on a 0.9 μm deep patterned sapphire substrate with stripes along the 〈1−100〉sapphire direction. Stripe-orientation dependent growth modes accounting for the observed experimental results are proposed.
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85.60.Jb Light-emitting devices

Finite element analysis of high-pressure anvils according to the principle of lateral support

Qigang Han, Hongan Ma, Rui Li, Lin Zhou, Yu Tian, Zhongzhu Liang, and Xiaopeng Jia

J. Appl. Phys. 102, 084504 (2007); http://dx.doi.org/10.1063/1.2785970 (4 pages) | Cited 4 times

Online Publication Date: 22 October 2007

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In order to extend the lifetime of an anvil made of tungsten carbide used in a large volume cubic high-pressure apparatus (CHPA), we analyzed the properties of an anvil with different magnitudes of interference, matching the steel supporting ring under high pressure using finite element method. It is found that the peak value and distribution of the von Mises stress does not change obviously when the magnitude of interference is smaller than 0.3 mm. When the magnitude of interference reaches 0.3 mm, the peak value of the von Mises stress and its distribution changes substantially, due to which the performance of the anvil can be significantly affected. Thus, the magnitude of interference ought to be between 0.1 and 0.25 mm. The simulated results have been approved in many high-pressure experiments in CHPA.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells

Annealing properties of vacancy-type defects in ion-implanted GaN studied by monoenergetic positron beams

A. Uedono, K. Ito, H. Nakamori, K. Mori, Y. Nakano, T. Kachi, S. Ishibashi, T. Ohdaira, and R. Suzuki

J. Appl. Phys. 102, 084505 (2007); http://dx.doi.org/10.1063/1.2798586 (7 pages) | Cited 11 times

Online Publication Date: 23 October 2007

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Defects in ion-implanted GaN and their annealing properties were studied by using monoenergetic positron beams. Doppler broadening spectra of the annihilation radiation and the positron lifetimes were measured for Si+, O+, and Be+-implanted GaN grown by the metal-organic chemical vapor deposition technique. First-principles calculations were also used to identify defect species introduced by the implantation. For as-implanted samples, the major defect species was identified as Ga vacancies and/or divacancies. An agglomeration of defects starts after annealing at 400 °C, and the defect profile shifted toward the surface with the open volumes of the defects increasing. The annealing properties of defects were found to depend on the ion species, and they are discussed here in terms of defect concentrations and interactions between impurities and defects.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.70.Bj Positron annihilation
61.72.uj III-V and II-VI semiconductors

Polysilane based organic light emitting diodes: Simultaneous ultraviolet and visible emission

Asha Sharma, Monica Katiyar, Deepak, and Shu Seki

J. Appl. Phys. 102, 084506 (2007); http://dx.doi.org/10.1063/1.2800173 (7 pages) | Cited 4 times

Online Publication Date: 24 October 2007

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While most organic light emitting diodes are designed to emit in the visible region, we report a series of polysilane based diodes for developing ultraviolet emitters at room temperature. These reported devices can also be controlled to simultaneously emit both ultraviolet and visible light, very close to the equienergy white point [Commission Internationale de l’Eclairage coordinate (0.33,0.33)]. Furthermore, the color coordinate of the visible emission is independent of the applied voltage. Therefore, the reported polysilane organic light emitting diodes can also be used as a white light source in which the ultraviolet emission from the same device provides an opportunity to modulate the color. While the origin of ultraviolet emission in electroluminescence is ascribed to an excitonic emission from the σ-σ* transition, consistent with its presence in the photoluminescence spectrum, we assign visible emission to defects states, based on degradation studies of the electroluminescent device.
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85.60.Jb Light-emitting devices

Effect of Li2CO3 addition on the dielectric and piezoelectric responses in the low-temperature sintered 0.5PZN–0.5PZT systems

Yu-Dong Hou, Li-Min Chang, Man-Kang Zhu, Xue-Mei Song, and Hui Yan

J. Appl. Phys. 102, 084507 (2007); http://dx.doi.org/10.1063/1.2800264 (7 pages) | Cited 13 times

Online Publication Date: 24 October 2007

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Low-temperature sintering of 0.5Pb(Zn1/3Nb2/3)O3–0.5Pb(Zr0.47Ti0.53)O3 ceramics (0.5PZN–0.5PZT) was investigated using Li2CO3 as sintering aids. The addition of Li2CO3 significantly improved the sinterability of 0.5PZN–0.5PZT ceramics, resulting in a reduction of sintering temperature from 1100 to 950 °C. Moreover, the effect of Li2CO3 addition on the dielectric and piezoelectric responses in 0.5PZN–0.5PZT systems was systematically studied in this work. The analysis of x-ray diffraction patterns and scanning electron microscopy indicated that the solubility limit of Li ions in perovskite structures was near 0.5 wt % in Li2CO3 form. Below the solubility limit, Li+ ions entered the six-fold coordinated B sites of oxygenic octahedral center and enhanced the compositional fluctuation in nanoscale, resulting in the increase of the degree of diffuseness γ. While at high doping level above the solubility limit, γ decreased subsequently, which was attributed to the formation of pyrochlore phase. Raman analysis on the B-site cation order correlates well with the dielectric measurement results. The large improvements in the piezoelectric properties such as the coupling factor and piezoelectric constant were also observed for doped specimens. Optimized parameters, such as d33 = 278 pC/N, kp = 0.50, and εmax = 8800, were achieved by doping 0.5 wt % Li2CO3 in low-temperature sintered 0.5PZN–0.5PZT systems, which shows great promise as practical materials for multilayered piezoelectric device applications. The observed improvement in the electric properties can be attributed to the grain size effect. After doping, the clamping effect caused by oxygen vacancies and grain boundary phases on domain wall motion was largely reduced due to the increase of grain size; therefore, a significant reduced coercive field and an increased remanent polarization were observed in doped 0.5PZN–0.5PZT systems.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ej Polarization and depolarization

Channel-length and gate-bias dependence of contact resistance and mobility for In2O3 nanowire field effect transistors

Gunho Jo, Jongsun Maeng, Tae-Wook Kim, Woong-Ki Hong, Byung-Sang Choi, and Takhee Lee

J. Appl. Phys. 102, 084508 (2007); http://dx.doi.org/10.1063/1.2799960 (7 pages) | Cited 11 times

Online Publication Date: 26 October 2007

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We demonstrate the scaling properties of the gate-bias-dependent transfer characteristics of In2O3 nanowire field effect transistors (FETs) studied using a conducting atomic force microscope. The contact resistance was extracted from the scaling of the resistance of an In2O3 nanowire FET with respect to its channel length. This contact resistance was found to be significant for short channel devices and decreased as the gate bias increased. We also investigated the apparent and intrinsic mobilities of the nanowire FET as a function of channel length and gate bias. It was determined that the intrinsic mobility could be corrected by considering the non-negligible contact resistance.
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85.30.Tv Field effect devices

Discrete-dopant-induced characteristic fluctuations in 16 nm multiple-gate silicon-on-insulator devices

Yiming Li and Chih-Hong Hwang

J. Appl. Phys. 102, 084509 (2007); http://dx.doi.org/10.1063/1.2801013 (6 pages) | Cited 16 times

Online Publication Date: 26 October 2007

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The impact of the number and position of discrete dopants on device characteristics is crucial in determining the behavior of nanoscale semiconductor devices. This study explores discrete-dopant-induced characteristic fluctuations in 16 nm single-, double-, triple-, and (square shape) surrounding-gate silicon-on-insulator (SOI) devices. Discrete dopants are statistically positioned in the three-dimensional channel region to examine associated carrier transportation characteristics, concurrently capturing “dopant concentration variation” and “dopant position fluctuation.” An experimentally validated simulation was conducted to investigate the threshold voltage (Vth) fluctuation and the variation of the on- and off-state currents of the four explored structures. The fluctuations of Vth of the double-, triple- and surrounding-gate devices are 2.2, 3.3 and 4 times smaller, respectively, than that of planar SOI. Results of this study provide further insight into the problem of fluctuation and the mechanism of immunity against fluctuation in ultrasmall field effect transistors (FETs) with vertical channel structures, such as fin-typed FETs.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Analysis of limitations of terahertz p-i-n uni-traveling-carrier photodiodes

Michael N. Feiginov

J. Appl. Phys. 102, 084510 (2007); http://dx.doi.org/10.1063/1.2801400 (12 pages) | Cited 3 times

Online Publication Date: 30 October 2007

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The uni-traveling-carrier p-i-n photodiodes have been analyzed both in the ballistic and drift modes of operation. The analytical expressions for the terahertz (THz) power achievable with the photodiodes have been derived in the drift-diffusion approximation, the optimum photodiode parameters have been identified and different THz-power limitation mechanisms (space-charge effects, heating, absorption saturation, etc.) have been considered. It has been shown that the THz powers on the level of 300 μW at ≳1 THz, 10 mW at 0.3 THz and 30 mW at 0.1 THz should be achievable. That would give more than an order of magnitude improvement as compared to the present state-of-the-art results. At the lower end of the THz-frequency range, the main limitation mechanisms are the heating and space-charge effects. At the higher frequencies, at ≳1 THz, the latter mechanism should play the major role.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Bt Optoelectronic device characterization, design, and modeling

An improved process for fabricating high-mobility organic molecular crystal field-effect transistors

A. P. Micolich, L. L. Bell, and A. R. Hamilton

J. Appl. Phys. 102, 084511 (2007); http://dx.doi.org/10.1063/1.2802284 (5 pages) | Cited 2 times

Online Publication Date: 30 October 2007

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In this paper we present an improved process for producing elastomer transistor stamps and high-mobility organic field-effect transistors (FETs) based on semiconducting acene molecular crystals. In particular, we have removed the need to use a silanized Si wafer for curing the stamps and to handle a fragile micron thickness polydimethylsiloxane (PDMS) insulating film and laminate it, bubble-free, against the PDMS transistor stamp. We find that despite the altered design, rougher PDMS surface, and lamination and measurement of the device in air, we still achieve electrical mobilities of the order of 10 cm2/V s, comparable to the current state of the art in organic FETs. Our device shows hole conduction with a threshold voltage of the order of −9 V, which corresponds to a trap density of 1.4×1010 cm−2.
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85.30.Tv Field effect devices
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