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19 Mar 2007

Volume 90, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages)

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg
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Deep level defects which limit current gain in 4H SiC bipolar junction transistors

C. J. Cochrane, P. M. Lenahan, and A. J. Lelis

Appl. Phys. Lett. 90, 123501 (2007); http://dx.doi.org/10.1063/1.2714285 (3 pages) | Cited 5 times

Online Publication Date: 19 March 2007

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The authors employ a very sensitive electrically detected electron spin resonance technique called spin dependent recombination to observe recombination centers in fully processed 4H SiC n-p-n bipolar junction transistors. Their measurements indicate that the observed dominating recombination defect in these transistors is an intrinsic center of high symmetry, most likely a vacancy. This defect likely plays a dominating role in limiting the current gain in these 4H SiC devices.
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85.30.Pq Bipolar transistors

Observation of negative bias stressing interface trapping centers in metal gate hafnium oxide field effect transistors using spin dependent recombination

C. J. Cochrane, P. M. Lenahan, J. P. Campbell, G. Bersuker, and A. Neugroschel

Appl. Phys. Lett. 90, 123502 (2007); http://dx.doi.org/10.1063/1.2715141 (3 pages) | Cited 4 times

Online Publication Date: 19 March 2007

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The authors combine metal oxide semiconductor (MOS) gated diode measurements and very sensitive electrically detected electron spin resonance measurements to detect and identify negative bias temperature instability (NBTI) generated defect centers in fully processed HfO2 pMOS field effect transistors. Both short and long term stressing defects are different from those generated by NBTI in Si/SiO2 devices. The spectra generated by long term stressing differ from the short term stressing signals and are somewhat similar to those observed in plasma nitrided oxide Si/SiO2 devices. The results suggest that NBTI defects are located in the interfacial SiO2 layer of these HfO2 devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Highly stable three-band white light from an InGaN-based blue light-emitting diode chip precoated with (oxy)nitride green/red phosphors

Chih-Chieh Yang, Chih-Min Lin, Yi-Jung Chen, Yi-Tsuo Wu, Shih-Ren Chuang, Ru-Shi Liu, and Shu-Fen Hu

Appl. Phys. Lett. 90, 123503 (2007); http://dx.doi.org/10.1063/1.2714326 (3 pages) | Cited 32 times

Online Publication Date: 20 March 2007

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A three-band white light-emitting diode (LED) was fabricated using an InGaN-based blue LED chip that emits 455 nm blue light, and green phosphor SrSi2O2N2:Eu and red phosphor CaSiN2:Ce that emit 538 nm green and 642 nm red emissions, respectively, when excited by the 455 nm blue light. The luminous efficacy of this white LED is about 30 lm/W at a dc of 20 mA. With increasing dc from 5.0 to 60 mA, both the coordinates x and y of the white LED tend to be the same, and consequently the Tc is the same and the Ra increases to 92.2.
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85.60.Jb Light-emitting devices

Nucleation switching in phase change memory

V. G. Karpov, Y. A. Kryukov, S. D. Savransky, and I. V. Karpov

Appl. Phys. Lett. 90, 123504 (2007); http://dx.doi.org/10.1063/1.2715024 (3 pages) | Cited 47 times

Online Publication Date: 20 March 2007

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The authors propose a simple physical model of threshold switching in phase change memory cells based on the field induced nucleation of conductive cylindrical crystallites. The model is solved analytically and leads to a number of predictions including correlations between the threshold voltage Vth and material parameters, such as the nucleation barrier and radius, amorphous layer thickness, as well as Vth versus temperature and switching delay time. The authors have carried out verifying experiments, and good agreement is achieved.
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64.60.Q- Nucleation
61.43.Fs Glasses

Anomalous behavior of AlGaN/GaN heterostructure field-effect transistors at cryogenic temperatures: From current collapse to current enhancement with cooling

H. F. Sun and C. R. Bolognesi

Appl. Phys. Lett. 90, 123505 (2007); http://dx.doi.org/10.1063/1.2715032 (3 pages) | Cited 6 times

Online Publication Date: 20 March 2007

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While current collapse affects AlGaN/GaN heterojunction field-effect transistors (HFETs) around room temperature, it gradually gives place to a current enhancement with cooling—below 200 K, electrically stressed devices do show higher currents than in their prestressed state. This behavior can be explained by increased levels of channel impact ionization at lower temperatures. The positive hole charge generated by impact ionization compensates (and eventually dominates) the parasitic negative charge that is responsible for current collapse at higher temperatures (i.e., the “virtual gate charge”). Cooling of AlGaN/GaN HFETs may potentially alleviate some of the nonidealities that have so far plagued this technology.
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85.30.Tv Field effect devices

High-efficiency deep blue host for organic light-emitting devices

Zhi Qiang Gao, Bao Xiu Mi, Chin H. Chen, Kow Wai Cheah, Yuen Kit Cheng, and Wen-Shih Wen

Appl. Phys. Lett. 90, 123506 (2007); http://dx.doi.org/10.1063/1.2715041 (3 pages) | Cited 30 times

Online Publication Date: 20 March 2007

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High-efficiency deep blue organic light-emitting devices have been fabricated using asymmetrically substituted 9-(α-naphthyl)-10-(β-naphthyl)-anthracene as blue host material and diphenyl-[4-(2-[1,1′;4′,1″]terphenyl-4-yl-vinyl)-phenyl]amine as dopant emitter. With an optimized device structure and doping concentration, the deep blue electroluminescent (EL) device achieved an EL efficiency of 4.9 cd/A and an external quantum efficiency of 4.4% at a current density of 20 mA/cm2 at saturated blue Commission Internationale de l’Eclairage coordinates of (0.15, 0.13). The deep blue device also has a current efficiency which is invariable with driving conditions ranging from 10 to 100 mA/cm2.
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85.60.Jb Light-emitting devices

Single Schottky-barrier photodiode with interdigitated-finger geometry: Application to diamond

Meiyong Liao, Yasuo Koide, and Jose Alvarez

Appl. Phys. Lett. 90, 123507 (2007); http://dx.doi.org/10.1063/1.2715440 (3 pages) | Cited 19 times

Online Publication Date: 20 March 2007

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The authors propose a single Schottky-barrier photodiode (SPD) with interdigitated Ohmic and Schottky contacts. A homoepitaxial diamond layer with low boron concentration has been utilized as an example for the fabrication of solar-blind deep-ultraviolet detector. This device structure enables the operations in both photoconductive mode with large photocurrent gain and depletion mode with fast response speed. The photosensitivity and spectral response of such kind of device are greatly improved when compared with a conventional SPD with semitransparent dotted Schottky contact. The present device structure can be extended to other semiconductor photodetectors.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
85.60.Gz Photodetectors (including infrared and CCD detectors)

Effects of molecular oxygen and ozone on polythiophene-based thin-film transistors

Michael L. Chabinyc, Robert A. Street, and John E. Northrup

Appl. Phys. Lett. 90, 123508 (2007); http://dx.doi.org/10.1063/1.2715445 (3 pages) | Cited 41 times

Online Publication Date: 20 March 2007

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The effects of exposure of polymeric thin-film transistors (TFTs) to the ambient atmosphere, oxygen, and ozone were investigated. The off-state current increased and the threshold voltage became more positive for TFTs made with several thiophene-based polymers when exposed to the ambient. Exposure to purified air did not change the characteristics of TFTs. Exposure to ozone caused similar changes as exposure to the ambient. Density functional calculations showed that ozone forms a complex with polythiophene, that is, a shallow acceptor. These results suggest that ozone in the ambient can cause changes in electrical characteristics of polythiophene-based TFTs rather than oxygen.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices

Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material

Hiroshi Kanno, Kaori Ishikawa, Yoshitaka Nishio, Ayataka Endo, Chihaya Adachi, and Kenichi Shibata

Appl. Phys. Lett. 90, 123509 (2007); http://dx.doi.org/10.1063/1.2643908 (3 pages) | Cited 26 times

Online Publication Date: 21 March 2007

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The red-emitting phosphorescent organic light-emitting device employing Bis[2-(2-benzothiazoyl)phenolato]zinc(II) (Zn(BTP)2) as a host material has been demonstrated. The device generates saturated red emission with Commission Internationale de l’Eclairage coordinates of (0.67, 0.33), characterized by a low driving voltage of 3.2 V and high external quantum efficiency of 10.3% at 10 mA/cm2. Moreover, the efficiency and lifetime are improved by using 30% NPB-doped Zn(BTP)2 host in the emitting layer, where NPB is 4,4′-bis(N-phenyl-1-naphthyl-amino)biphenyl. The maximum external quantum efficiency of the device reaches 12.6% at 1.7 mA/cm2. The device has exhibited excellent stability. The half-luminance lifetime is 240 h at 80 mA/cm2 (initial luminance of 6070 cd/m2). The relationship between the employed host material and device performance is discussed.
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85.60.Jb Light-emitting devices

Transmission line impedance of carbon nanotube thin films for chemical sensing

G. Esen, M. S. Fuhrer, M. Ishigami, and E. D. Williams

Appl. Phys. Lett. 90, 123510 (2007); http://dx.doi.org/10.1063/1.2709995 (3 pages) | Cited 4 times

Online Publication Date: 22 March 2007

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The authors measure the resistance and frequency-dependent gate capacitance of carbon nanotube (CNT) thin films in ambient, vacuum, and under low pressure (10−6 Torr) analyte environments. They model the CNT film as a RC transmission line and show that changes in the measured capacitance as a function of gate bias and analyte pressure are consistent with changes in the transmission line impedance due to changes in the CNT film resistivity alone; the electrostatic gate capacitance of the CNT film does not depend on gate voltage or chemical analyte adsorption. However, the CNT film resistance is enormously sensitive to low pressure analyte exposure.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.63.Fg Nanotubes
73.61.Wp Fullerenes and related materials

Comparison of metal-oxide-semiconductor capacitors on c- and m-plane gallium nitride

Kevin Matocha, Vinayak Tilak, and Greg Dunne

Appl. Phys. Lett. 90, 123511 (2007); http://dx.doi.org/10.1063/1.2716309 (2 pages) | Cited 15 times

Online Publication Date: 23 March 2007

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The properties of the SiO2/GaN interface were characterized using metal-oxide-semiconductor capacitors on polar c-plane (0001) and nonpolar m-plane (0 1 -1 0) GaN crystal faces. GaN m-plane samples show the absence of pyroelectric polarization effects. Additionally, capacitance-voltage hysteresis is less on m-plane compared to c-plane GaN surfaces, suggesting a lower interface-state density at the m-plane GaN/SiO2 interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Room temperature pulsed laser deposited indium gallium zinc oxide channel based transparent thin film transistors

Arun Suresh, Patrick Wellenius, Anuj Dhawan, and John Muth

Appl. Phys. Lett. 90, 123512 (2007); http://dx.doi.org/10.1063/1.2716355 (3 pages) | Cited 57 times

Online Publication Date: 23 March 2007

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Indium gallium zinc oxide deposited by pulsed laser deposition at room temperature was used as a channel layer to fabricate transparent thin film transistors with good electrical characteristics: field effect mobility of 11 cm2 V−1 s−1 and subthreshold voltage swing of 0.20 V/decade. By varying the oxygen partial pressure during deposition the conductivity of the channel was controlled to give a low off-current of ∼ 10 pA and a drain current on/off ratio of ∼ 5×107. Changing the channel layer thickness was a viable way to vary the threshold voltage. The effect of the gate dielectric on the electrical behavior was also explored.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology

Improved transport properties of Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistor

P. Kordoš, D. Gregušová, R. Stoklas, K. Čičo, and J. Novák

Appl. Phys. Lett. 90, 123513 (2007); http://dx.doi.org/10.1063/1.2716846 (3 pages) | Cited 31 times

Online Publication Date: 23 March 2007

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The authors report on improved transport properties of Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). It is found that the drift mobility in the MOSHFET structures with 4 nm thick Al2O3 gate oxide is significantly higher than that in HFETs. The zero-bias mobilities are 1950 and 1630 cm2/V s for the MOSHFET and HFET, respectively. An ∼ 40% increase of the saturation drain current in the MOSHFETs compared to the HFETs seems to be larger than expected from the passivation effects. The MOSHFET devices show a higher transconductance (with peak values of ∼ 115 mS/mm) than the HFETs ( ∼ 70 mS/mm). Analysis of the device performance indicates a decrease of the parasitic series resistance together with an enhancement of the effective velocity of the channel electrons in the MOSHFET devices.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Nanomesh fluidic filter using self-assembly of colloidal nanospheres and surface tension

Young Ho Seo

Appl. Phys. Lett. 90, 123514 (2007); http://dx.doi.org/10.1063/1.2715040 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2007

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A simple and inexpensive method of fabricating a nanofluidic filter was developed by using self-assembly of colloidal nanospheres and surface tension. Colloid plug formed by surface tension in the microchannel was evaporated, then the nanospheres in a colloid were orderly stacked by capillary force. The porosity and mean pore size of the nanomesh membrane were 45.4% and 158 nm, respectively. In the nanoindentation test with a spherical tip of 10 μm radius, the nanomesh membranes withstood the maximum mechanical loading of 26.8±2.47 mN, and the heat-treated membranes withstood 66.65±4.15 mN.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
81.16.Dn Self-assembly
82.70.Dd Colloids
68.03.Cd Surface tension and related phenomena
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