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2 Jan 2006

Volume 88, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 88, 011112 (2006); http://dx.doi.org/10.1063/1.2161387 (3 pages)

Yoshinori Tanaka, Takashi Asano, Ranko Hatsuta, and Susumu Noda
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GaInN light-emitting diode with conductive omnidirectional reflector having a low-refractive-index indium-tin oxide layer

Jong Kyu Kim, Thomas Gessmann, E. Fred Schubert, J.-Q. Xi, Hong Luo, Jaehee Cho, Cheolsoo Sone, and Yongjo Park

Appl. Phys. Lett. 88, 013501 (2006); http://dx.doi.org/10.1063/1.2159097 (3 pages) | Cited 51 times

Online Publication Date: 3 January 2006

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Enhancement of light extraction in a GaInN light-emitting diode (LED) employing a conductive omnidirectional reflector (ODR) consisting of GaN, an indium-tin oxide (ITO) nanorod low-refractive-index layer, and an Ag layer is presented. An array of ITO nanorods is deposited on p-type GaN by oblique-angle electron-beam deposition. The refractive index of the nanorod ITO layer is 1.34 at 461 nm, significantly lower than that of dense ITO layer, which is n = 2.06. The GaInN LEDs with GaN/low-n ITO/Ag ODR show a lower forward voltage and a 31.6% higher light-extraction efficiency than LEDs with Ag reflector. This is attributed to enhanced reflectivity of the ODR that employs the low-n ITO layer.
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85.60.Jb Light-emitting devices

Synthesis of electron transmission in nanoscale semiconductor devices

Petra Schmidt, Stephan Haas, and A. F. J. Levi

Appl. Phys. Lett. 88, 013502 (2006); http://dx.doi.org/10.1063/1.2159102 (3 pages) | Cited 5 times

Online Publication Date: 3 January 2006

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Adaptive design may be used to synthesize a conduction band potential profile to obtain desired nonequilibrium electron transmission-voltage characteristics. Our methodology is illustrated by designing a two-terminal linear element in which electron motion is limited by quantum mechanical transmission through a potential profile.
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85.30.De Semiconductor-device characterization, design, and modeling
85.35.-p Nanoelectronic devices

Evolution of luminance by voltage in organic light-emitting diodes

Byung Mook Weon, Soo Young Kim, Jong-Lam Lee, and Jung Ho Je

Appl. Phys. Lett. 88, 013503 (2006); http://dx.doi.org/10.1063/1.2159563 (3 pages)

Online Publication Date: 3 January 2006

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We study degradation behaviors of luminance and voltage in organic light-emitting diodes. We find that normalized luminance and inverse normalized voltage with time, L(t) and V(t)−1, follow the stretched exponential decay. On this basis, we derive a general relation of luminance and voltage with time as L(t) = V(t)−δ(t), where δ(t) indicates a decay exponent, which is attributed to time-dependent space-charge limitation. Here the observation of higher δ(t) at higher initial luminance explains why luminance decay is faster at higher initial luminance.
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85.60.Jb Light-emitting devices

Ozone passivation of slow transient current collapse in AlGaN/GaN field-effect transistors: The role of threading dislocations and the passivation mechanism

D. W. DiSanto, H. F. Sun, and C. R. Bolognesi

Appl. Phys. Lett. 88, 013504 (2006); http://dx.doi.org/10.1063/1.2161810 (3 pages) | Cited 9 times

Online Publication Date: 4 January 2006

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Current collapse in AlGaN/GaN field-effect transistors subjected high rf drive levels and/or to bias stresses is attributed to the presence of surface trapping levels whose nature remains to be identified. Although current collapse manifestations can be alleviated with various surface films, the exact passivation mechanism remains a matter of debate. We show that slow transient current collapse can be eliminated by a short ozone exposure, unambiguously tying current collapse to the sample surface, without invoking strain or dielectric encapsulation arguments. We assert that the surface states responsible for slow collapse arise where dislocations intersect the sample surface, and propose an alternative current collapse mechanism wherein individual dislocation lines result in multiple discrete virtual gates that locally deplete the transistor channel access regions.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Effect of hydrostatic pressure on the dc characteristics of AlGaN/GaN heterojunction field effect transistors

Y. Liu, P. P. Ruden, J. Xie, H. Morkoç, and K.-A. Son

Appl. Phys. Lett. 88, 013505 (2006); http://dx.doi.org/10.1063/1.2161812 (3 pages) | Cited 13 times

Online Publication Date: 4 January 2006

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We report the effect of compressive hydrostatic pressure on the current-voltage characteristics of AlGaN/GaN heterojunction field effect transistors (HFETs) on a sapphire substrate. The drain current increases with hydrostatic pressure and the maximum relative increase occurs when the gate bias is near threshold and drain bias is slightly larger than saturation bias. The increase of the drain current is associated with a pressure induced shift of the threshold voltage by −8.0 mV/kbar that is attributed to an increase of the polarization charge density at the AlGaN/GaN interface due to the piezoelectric effect. The results demonstrate the considerable potential of AlGaN/GaN HFETs for strain sensor applications.
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85.30.Tv Field effect devices

Surface oxide relationships to band bending in GaN

Michael A. Garcia, Scott D. Wolter, Tong-Ho Kim, Soojeong Choi, Jamie Baier, April Brown, Maria Losurdo, and Giovanni Bruno

Appl. Phys. Lett. 88, 013506 (2006); http://dx.doi.org/10.1063/1.2158701 (3 pages) | Cited 13 times

Online Publication Date: 4 January 2006

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A trend of increased near-surface valence band maximum band bending with increasing O/Ga relative fraction was observed, extrapolating to 2.7 eV±0.1 eV for pristine GaN surfaces (0% O 1s peak area). This trend of apparent oxide overlayer coverage affecting the band bending linearly could lead to better understanding and characterization of oxidized GaN surfaces to control band bending for sensors or other devices.
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73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds

Strain dependence of Si–Ge interdiffusion in epitaxial Si/Si1−yGey/Si heterostructures on relaxed Si1−xGex substrates

Guangrui Xia, Oluwamuyiwa O. Olubuyide, Judy L. Hoyt, and Michael Canonico

Appl. Phys. Lett. 88, 013507 (2006); http://dx.doi.org/10.1063/1.2158706 (3 pages) | Cited 13 times

Online Publication Date: 4 January 2006

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The strain dependence of Si–Ge interdiffusion in epitaxial Si/Si1−yGey/Si heterostructures on relaxed Si1−xGex substrates has been studied using secondary ion mass spectrometry, Raman spectroscopy, and simulations. At 800 and 880 °C, significantly enhanced Si–Ge interdiffusion is observed in Si/Si1−yGey/Si heterostructures (y = 0.56, 0.45, and 0.3) with Si1−yGey layers under compressive strain of −1%, compared to those under no strain. In contrast, tensile strain of 1% in Si0.70Ge0.30 layer has no observable effect on interdiffusion in Si/Si0.70Ge0.30/Si heterostructures. These results are relevant to the device and process design of high mobility dual channel and heterostructure-on-insulator metal oxide semiconductor field effect transistors.
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68.35.Fx Diffusion; interface formation
78.66.Db Elemental semiconductors and insulators
68.60.Bs Mechanical and acoustical properties
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
78.30.Hv Other nonmetallic inorganics

Carbon-nanotube-based single-electron/hole transistors

Hong Li, Qing Zhang, and Jingqi Li

Appl. Phys. Lett. 88, 013508 (2006); http://dx.doi.org/10.1063/1.2161017 (3 pages) | Cited 7 times

Online Publication Date: 4 January 2006

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Single-walled-carbon-nanotube (SWNT)-based single-electron/hole devices are fabricated with long SWNT channel surrounded by several short SWNTs on the electrodes. The channel current of the device is suggested to be controlled by the Schottky barriers, which are very sensitive to the electrostatic potential at the SWNT/electrode contacts. Coulomb blockade phenomena in the channel current below 70 K suggest two-fold effects caused by single electron/hole charging the short SWNTs: (1) The charged short SWNTs have a significant characteristic of Coulomb blockade, and (2) the electrostatic potential of charged short SWNTs modify the Schottky barrier, and hence the channel current.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
85.35.Kt Nanotube devices

Vertically integrated thin-film color sensor arrays for advanced sensing applications

H. Steibig, R. A. Street, D. Knipp, M. Krause, and J. Ho

Appl. Phys. Lett. 88, 013509 (2006); http://dx.doi.org/10.1063/1.2140072 (3 pages) | Cited 4 times

Online Publication Date: 5 January 2006

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A three-color sensor array based on a vertically integrated thin-film structure is reported. The complete color information can be detected at the same position of a sensor array without using optical filters. The sensors consist of a multilayer thin-film system utilizing amorphous silicon and its alloys. The spectral sensitivity of the sensors is controlled by the optical properties of the materials and the applied bias voltage. The color sensors were integrated with amorphous silicon readout electronics to realize a large area thin-film three color sensor array. The working principle of the thin-film sensor arrays is presented with a discussion of the spectral sensitivity and the pixel cross talk.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.82.-m Integrated optics
85.60.-q Optoelectronic devices

Influence of dehydrated nanotubed titanic acid on polymer light-emitting diodes with phosphorescent dye

L. Qian, T. Zhang, Y. S. Wang, X. R. Xu, Z. S. Jin, and Z. L. Du

Appl. Phys. Lett. 88, 013510 (2006); http://dx.doi.org/10.1063/1.2163987 (3 pages) | Cited 5 times

Online Publication Date: 6 January 2006

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In this letter, we demonstrate that hole injection and transport in polymer light-emitting diodes with phosphorescent dye Ir(ppy)3 can be significantly enhanced by doping p-type conductive dehydrated nanotubed titanic acid into poly(vinylcarbazole) (PVK) films at 2 wt. %. At the same time, both energy transfer and exciton recombination efficiency are improved because of the open and straight conformation of the PVK molecule in the nanocomposite. The performance of these devices was greatly improved, showing higher luminance, enhanced efficiency, and a lower turn-on voltage.
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85.60.Jb Light-emitting devices
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