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23 Apr 2007

Volume 90, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 90, 173502 (2007); http://dx.doi.org/10.1063/1.2732163 (3 pages)

Matthias Imboden, Pritiraj Mohanty, Alexei Gaidarzhy, Janet Rankin, and Brian W. Sheldon
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High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

Sung Hyun Kim, Jyongsik Jang, Jae-Min Hong, and Jun Yeob Lee

Appl. Phys. Lett. 90, 173501 (2007); http://dx.doi.org/10.1063/1.2731435 (3 pages) | Cited 22 times

Online Publication Date: 23 April 2007

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Light emission in phosphorescent quantum well structure which can confine excitons within an emitting layer was investigated. A multilayer quantum well structure which has a narrow triplet band gap host material sandwiched between wide triplet band gap host materials was designed, and device performances were studied. The multilayer emitting structure gave high efficiency of 47 cd/A compared with 11 cd/A of standard green devices.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Scaling of dissipation in megahertz-range micromechanical diamond oscillators

Matthias Imboden, Pritiraj Mohanty, Alexei Gaidarzhy, Janet Rankin, and Brian W. Sheldon

Appl. Phys. Lett. 90, 173502 (2007); http://dx.doi.org/10.1063/1.2732163 (3 pages) | Cited 24 times

Online Publication Date: 23 April 2007

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The authors report frequency and dissipation scaling laws for doubly clamped diamond resonators. The device lengths range from 10 to 19 μm corresponding to frequency and quality-factor ranges of 17 to 66 MHz and 600–2400, respectively. The authors find that the resonance frequency scales as 1/L2 confirming the validity of the thin-beam approximation. The dominant dissipation comes from two sources: for the shorter beams, clamping loss is the dominant dissipation mechanism, while for the longer beams, surface losses provide a significant source of dissipation. The authors compare and contrast these mechanisms with other dissipation mechanisms to describe the data.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Ring waveguide resonator on surface acoustic waves

S. V. Biryukov, G. Martin, and M. Weihnacht

Appl. Phys. Lett. 90, 173503 (2007); http://dx.doi.org/10.1063/1.2731683 (2 pages) | Cited 1 time

Online Publication Date: 23 April 2007

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A simple regular electrode structure for surface acoustic wave (SAW) devices is proposed. The structure consists of an interdigital transducer in the form of a ring placed on the Z cut of a hexagonal piezoelectric crystal. Finite thickness electrodes produce the known slowing effect for a SAW in comparison with this SAW on a free surface. The closed “slow” electrode region with the “fast” surrounding region forms an open waveguide resonator structure with the acoustic field concentrated in the electrode region. If the radius of the structure is large enough for a given wavelength, an acceptable level of radiation losses can be reached. The electrical admittance of such resonator does not have sidelobes.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effect of gate-source and gate-drain Si3N4 passivation on current collapse in AlGaN/GaN high-electron-mobility transistors on silicon

S. Arulkumaran, G. I. Ng, and Z. H. Liu

Appl. Phys. Lett. 90, 173504 (2007); http://dx.doi.org/10.1063/1.2730748 (3 pages) | Cited 10 times

Online Publication Date: 24 April 2007

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The effects of gate-source (GS) and gate-drain (GD) region passivation on the drain current (ID) collapse in AlGaN/GaN high-electron-mobility transistors (HEMTs) were studied. Electrical stresses were applied to the GS and GD regions of HEMTs, (1) unpassivated (device A), (2) fully passivated (device B), (3) GD passivated only (device C), and (4) device C with additional full passivation (device D). An increase of ID density and the extrinsic transconductance was observed in devices with full Si3N4 passivation. Due to the increase of gate leakage current by Si3N4 passivation, breakdown voltage decreases. Device A exhibited severe (96%) ID collapse when it was electrically stressed in both the GS and GD regions. Devices C and D have suppressed only 14% of ID collapse after passivation. However, HEMTs with full Si3N4 passivation (device B) have suppressed more than 80% of the ID collapse. Full passivation is required to suppress the ID collapse effectively for AlGaN/GaN HEMTs. The remaining ID collapse (19%) of device B is affected primarily by bulk/buffer related traps rather than surface related traps.
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85.30.Tv Field effect devices

Improved hole-injection contact for top-emitting polymeric diodes

Juo-Hao Li, Jinsong Huang, and Yang Yang

Appl. Phys. Lett. 90, 173505 (2007); http://dx.doi.org/10.1063/1.2731684 (3 pages) | Cited 25 times

Online Publication Date: 24 April 2007

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In this letter, an efficient hole-injection contact was achieved for the top-emitting polymeric light-emitting diodes (PLEDs). The anode has a structure of metal/molybdenum oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). It has been found that hole injection was significantly improved by inserting a thin layer of MoO3 between aluminum and PEDOT:PSS. An ultraviolet photoelectron spectroscopy (UPS) was used to investigate the change of work function, and photovoltaic measurement confirmed that the improved hole injection is due to the reduction of barrier height, resulted from the addition of transition metal oxide. PEDOT:PSS layer was found necessary in anode structure to further enhance the hole injection and electroluminance efficiency. A peak power efficiency of 11.42 lm/W was achieved at current density of 1.2 mA/cm2 for the white emission top-emitting PLEDs.
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85.60.Jb Light-emitting devices

AlN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor on 4 in. silicon substrate for high breakdown characteristics

S. Lawrence Selvaraj, Tsuneo Ito, Yutaka Terada, and Takashi Egawa

Appl. Phys. Lett. 90, 173506 (2007); http://dx.doi.org/10.1063/1.2730751 (3 pages) | Cited 12 times

Online Publication Date: 25 April 2007

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AlN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) grown on 4 in. silicon substrate have been demonstrated. The heterostructure exhibited high sheet carrier density with small surface roughness. AlN/AlGaN/GaN MIS-HEMT exhibited maximum drain current density (IDS max) of 361 mA/mm and maximum extrinsic transconductance (gm max) of 152 mS/mm. Due to the increase of sheet carrier density, the 2DEG channel shifts towards the AlGaN/GaN interface resulting in positive shift of the threshold voltage (−2.6 to −1.8 V). Two orders of magnitude low gate leakage current and reduced drain current collapse with high breakdown voltage of 230 V have been observed on AlN/AlGaN/GaN MIS-HEMTs.
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85.30.Tv Field effect devices

Organic light-emitting devices integrated with solar cells: High contrast and energy recycling

Chih-Jen Yang, Ting-Yi Cho, Chun-Liang Lin, and Chung-Chih Wu

Appl. Phys. Lett. 90, 173507 (2007); http://dx.doi.org/10.1063/1.2732181 (3 pages) | Cited 20 times

Online Publication Date: 25 April 2007

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In this letter, the authors report that by integrating organic light-emitting devices (OLEDs) with solar cells, luminous ambient-light reflection as low as 1.4% (even superior to that achieved with polarizers) can be achieved without compromising the electroluminescence efficiency for high-contrast display applications. Furthermore, in such a configuration, the photon energies of the incident ambient light and the portion of OLED emission not getting outside of the device can be recycled into useful electrical power via the photovoltaic action, instead of being totally wasted as in other reported contrast-enhancement techniques. These features, the authors believe, shall make this technique attractive for high-contrast display applications and portable/mobile electronics that are highly power aware.
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85.60.Jb Light-emitting devices
84.60.Jt Photoelectric conversion
85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices

Precise frequency estimation in a microelectromechanical parametric resonator

Michael V. Requa and Kimberly L. Turner

Appl. Phys. Lett. 90, 173508 (2007); http://dx.doi.org/10.1063/1.2732172 (3 pages) | Cited 9 times

Online Publication Date: 25 April 2007

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The authors report here on precise resonant frequency estimation using the nonlinear spectral features of parametric resonance. Demonstration of 100 parts per 109 frequency resolution at room temperature is accompanied by a technique to observe the phase trajectories of escape in bistable parametrically resonant systems. The system offers an expanded dynamic range over similar linear resonators. Precise frequency estimation has implications in resonant mass sensing.
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07.10.Cm Micromechanical devices and systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.-e Optical elements, devices, and systems

Electronic properties of a 3C/4H SiC polytype heterojunction formed on the Si face

M. V. S. Chandrashekhar, Christopher I. Thomas, Jie Lu, and M. G. Spencer

Appl. Phys. Lett. 90, 173509 (2007); http://dx.doi.org/10.1063/1.2730738 (3 pages) | Cited 7 times

Online Publication Date: 26 April 2007

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The authors report on the electronic properties of a rectifying Si face 3C/4H SiC heteropolytype junction on n+ 4H SiC. Capacitance-voltage profiling of the junction at temperatures from 4–300 K showed high apparent carrier concentration. A semiclassical model was used to explain the behavior. The model predicted a spontaneous polarization-induced valence band quantum well in the 3C, indicating a polarization charge of 9.7×1012 cm−2 for 4H SiC, in good agreement with theory. The formation of a two-dimensional hole gas was predicted. Using a Poisson-Schrödinger solver to analyze the measurements, it was found that large ( ∼ 3.5×1012 cm−2) mobile hole charge was induced in the n-doped 3C SiC.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
73.63.Hs Quantum wells

Quantum dot structures grown on Al containing quaternary material for infrared photodetection beyond 10 μm

P. L. Souza, A. J. Lopes, T. Gebhard, K. Unterrainer, M. P. Pires, J. M. Villas-Boas, G. S. Vieira, P. S. S. Guimarães, and Nelson Studart

Appl. Phys. Lett. 90, 173510 (2007); http://dx.doi.org/10.1063/1.2733603 (3 pages) | Cited 4 times

Online Publication Date: 26 April 2007

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Different InAs quantum dot structures grown on InGaAlAs lattice matched to InP were investigated for quantum dot infrared photodetectors. Extremely narrow photocurrent peaks were observed, demonstrating great potential for fine wavelength selection. Structures which can detect radiation beyond 10 μm were developed. Polarization dependence measurements showed that the structures have a zero-dimensional character and are suitable for detection of normal incident light. On the other hand, structures containing coupled quantum wells showed a hybrid two-dimensional/zero-dimensional behavior.
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78.67.Hc Quantum dots
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects

Low voltage complementary thin-film transistor inverters with pentacene-ZnO hybrid channels on AlOx dielectric

Min Suk Oh, D. K. Hwang, Kimoon Lee, Seongil Im, and S. Yi

Appl. Phys. Lett. 90, 173511 (2007); http://dx.doi.org/10.1063/1.2732819 (3 pages) | Cited 18 times

Online Publication Date: 26 April 2007

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The authors report on the fabrication of complementary thin-film transistor (CTFT) inverters with pentacene (p type) and ZnO (n type) hybrid channels on rf-deposited AlOx dielectrics. All deposition processes were carried out on glass substrates at low temperatures (<100 °C). Since our p-channel TFT showed somewhat equivalent field mobility of 0.11 cm2/V s compared to that of the n-channel device (0.75 cm2/V s), the hybrid CTFT inverters were designed with identical dimensions for both channels. The CTFT device demonstrated an excellent voltage gain of ∼ 21 with a low static power dissipation of ∼ 1.5 nW at a low supply voltage of 7 V.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Hysteresis of pentacene thin-film transistors and inverters with cross-linked poly(4-vinylphenol) gate dielectrics

Sang Chul Lim, Seong Hyun Kim, Jae Bon Koo, Jung Hun Lee, Chan Hoe Ku, Yong Suk Yang, and Taehyoung Zyung

Appl. Phys. Lett. 90, 173512 (2007); http://dx.doi.org/10.1063/1.2733626 (3 pages) | Cited 50 times

Online Publication Date: 26 April 2007

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The authors report the effects of hydroxyl groups (OH bonds) on the electrical reliabilities of pentacene organic thin-film transistors (OTFTs) with poly-4-vinylphenol (PVP) gate dielectrics. PVP gate dielectric films mixed with different concentrations of methylated poly(melamine-co-formaldehyde) (MMF) were fabricated, and experiments on the hysteresis behavior of the OTFT device were conducted. Pentacene TFTs with the PVP (MMF 0 wt.  %) exhibited a large hysteresis, while in the PVP (MMF 125 wt. %), nearly no hysteresis was observed. Large hysteresis observed in OTFT devices was confirmed to be strongly related to the hydroxyl groups existing inside of the polymeric dielectrics and could reduced by the decrease of OH group.
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85.30.Tv Field effect devices

Electron spin resonance observations of oxygen deficient silicon atoms in the interfacial layer of hafnium oxide based metal-oxide-silicon structures

J. T. Ryan, P. M. Lenahan, G. Bersuker, and P. Lysaght

Appl. Phys. Lett. 90, 173513 (2007); http://dx.doi.org/10.1063/1.2734478 (3 pages) | Cited 12 times

Online Publication Date: 27 April 2007

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Conventional electron spin resonance measurements indicate gross processing dependent differences in the densities of paramagnetic oxygen deficient silicon sites, E′ centers, in the interfacial layer of unstressed hafnium oxide based metal-oxide-silicon structures. (E′ centers are not usually observed in unstressed oxides.) The volume densities of these centers can be quite high ( ∼ 1×1019 cm−3). Electrically detected magnetic resonance measurements suggest that related oxygen deficient sites may significantly degrade device performance and reliability.
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85.30.Tv Field effect devices
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