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14 Mar 2005

Volume 86, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 86, 113104 (2005); http://dx.doi.org/10.1063/1.1883725 (3 pages)

S. Bhattacharyya, C. Sinturel, J. P. Salvetat, and M.-L. Saboungi
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Surface passivation using ultrathin AlNx film for Ge–metal–oxide–semiconductor devices with hafnium oxide gate dielectric

Fei Gao, S. J. Lee, J. S. Pan, L. J. Tang, and Dim-Lee Kwong

Appl. Phys. Lett. 86, 113501 (2005); http://dx.doi.org/10.1063/1.1875733 (3 pages) | Cited 23 times

Online Publication Date: 7 March 2005

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A surface passivation method to improve the film quality of HfO2 gate dielectric on Ge substrate by using ultrathin AlNx layer is reported. Results show that the AlNx passivation layer is more effective in suppressing the GeOx formation at the HfO2/Ge interface, resulting in improved C–V characteristics, than surface nitridation-passivated Ge devices. In addition, a thermal stability study shows AlNx passivation is promising for future Ge metal–oxide–semiconductor devices.
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84.32.Tt Capacitors
81.65.Rv Passivation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.60.Dv Thermal stability; thermal effects

Dependence of the programming window of silicon-on-insulator nanocrystal memories on channel width

G. Fiori, G. Iannaccone, G. Molas, and B. De Salvo

Appl. Phys. Lett. 86, 113502 (2005); http://dx.doi.org/10.1063/1.1884263 (3 pages) | Cited 7 times

Online Publication Date: 8 March 2005

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In this letter, we investigate the observed dependence of the programming window of silicon-on-insulator (SOI) nanocrystal memories on the width of the channel. Indeed, experiments show that the obtained threshold voltage shift after programming strongly increases with decreasing channel width. We show that such behavior is due to the preferential injection of electrons, during the program operation, from regions close to the edges of the SOI channel, where the electric field is stronger. As a consequence, charge is mostly stored in the dots in the oxide region surrounding the edges, and therefore is more and more effective as the channel width is decreased. Our conjecture is verified through dedicated three-dimensional simulations and checked against other mechanisms proposed in the literature.
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84.30.Sk Pulse and digital circuits
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Tv Field effect devices

Evidence of gap state formed by the charge transfer in Alq3/NaCl/Al interface studied by ultraviolet and x-ray photoelectron spectroscopy

Yeonjin Yi, Seong Jun Kang, Kwanghee Cho, Jong Mo Koo, Kyul Han, Kyongjin Park, Myungkeun Noh, Chung-Nam Whang, Kwangho Jeong, and Eun Joo Hahn

Appl. Phys. Lett. 86, 113503 (2005); http://dx.doi.org/10.1063/1.1884264 (3 pages) | Cited 11 times

Online Publication Date: 8 March 2005

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Electronic structures of Alq3/NaCl/Al and Alq3/Al were studied by UV and x-ray photoelectron spectroscopy (XPS). The initial energy level of the highest occupied molecular orbital (HOMO) of Alq3/Al was shifted when the ultrathin NaCl layer was inserted between them, although the vacuum level was not changed. The measured interface dipole was 1.1 eV, identical for both Alq3/NaCl/Al and Alq3/Al. Our experiment shows that the dipole is formed in very short range (less than 0.1 nm) from the interface. The onset of the HOMO level of Alq3 was shifted 0.2 eV toward high binding energy for the additional NaCl layer, which lowered the barrier height and improved injection characteristics of the device. Moreover, a gap state was observed at 1.1 eV below the Fermi level when the NaCl was inserted between Alq3 and Al. The XPS core-level spectra revealed that the interaction on Alq3 and NaCl was very weak, which generated an unusual gap state without breaking or forming chemical bonds. We suggest that the weak interaction would originate from the charge transfer from Alq3 to NaCl.
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85.60.Jb Light-emitting devices
73.21.Ac Multilayers
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Dp Adsorbed layers and thin films

Direct patterning of organic light-emitting devices by organic-vapor jet printing

Yiru Sun, Max Shtein, and Stephen R. Forrest

Appl. Phys. Lett. 86, 113504 (2005); http://dx.doi.org/10.1063/1.1884265 (3 pages) | Cited 8 times

Online Publication Date: 8 March 2005

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We demonstrate small molecular weight, fluorescent organic light-emitting devices directly patterned by organic-vapor jet printing (OVJP). In OVJP, a hot inert carrier gas picks up a molecular organic vapor that expands when passed through a nozzle, resulting in physisorption of the molecules onto a cooled substrate. A (1 cm)2 flat organic semiconductor thin film is achieved by sweeping the nozzle over the substrate to print closely spaced lines. Using an array of nozzles, multiple parallel stripes are simultaneously printed at a growth rate of 3.4 Å cm2/s. Organic heterostructure fluorescent-light-emitting devices consisting of a broad area hole transport layer, followed by a striped electron transport layer, both printed by OVJP, yield an external quantum efficiency of (0.84±0.03)%, which is comparable to that of similar devices deposited by vacuum thermal evaporation.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
68.43.Mn Adsorption kinetics
78.55.Kz Solid organic materials
73.50.Fq High-field and nonlinear effects

White organic light-emitting diodes based on spectral broadening in electroluminescence due to formation of interfacial exciplexes

Samarendra P. Singh, Y. N. Mohapatra, M. Qureshi, and S. Sundar Manoharan

Appl. Phys. Lett. 86, 113505 (2005); http://dx.doi.org/10.1063/1.1884255 (3 pages) | Cited 14 times

Online Publication Date: 9 March 2005

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We demonstrate white organic light-emitting diodes (OLEDs) having spectral width of approximately 260 nm in electroluminescence (EL) in a simple bilayer structure, consisting of TPD and zinc benzothiazole, without taking recourse to complex strategies such as blending and doping. The EL is broader than the corresponding photoluminescence (PL) of both component materials and their structures. A deconvolution of PL and EL spectra shows that as large as 60% of the broad EL emission originates from multiple exciplexes formed at the interface during electrical excitation.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Capacitance-spectroscopy identification of a key defect in N-degraded GalnNAs solar cells

Sarah Kurtz, Steve Johnston, and Howard M. Branz

Appl. Phys. Lett. 86, 113506 (2005); http://dx.doi.org/10.1063/1.1884267 (3 pages) | Cited 16 times

Online Publication Date: 9 March 2005

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We report a study comparing the device performance and the deep-level transient spectroscopy spectra of Ga1−yInyNxAs1−x diodes. It is found that a transient capacitance signal, which corresponds to a trap 0.18 to 0.25 eV below the conduction-band edge, is observed near 140 K in the nitrogen-containing samples. The existence of this transient correlates with higher dark current [lower open-circuit voltage (Voc)] and the size of the transient increases with x for x ⩽ 0.6%. The abrupt decrease of the Voc with the addition of nitrogen is explained by the hypothesis that a close approach of the electron quasi-Fermi level to the conduction-band edge is arrested by the electron trap. The N-induced trap level reduces Voc as if it were a new conduction-band edge.
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84.60.Jt Photoelectric conversion
85.30.Kk Junction diodes

White organic light-emitting diode comprising of blue fluorescence and red phosphorescence

Dashan Qin and Ye Tao

Appl. Phys. Lett. 86, 113507 (2005); http://dx.doi.org/10.1063/1.1879108 (3 pages) | Cited 51 times

Online Publication Date: 10 March 2005

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A white organic light-emitting diode with the structure of ITO/NPB 30 nm/TCTA+2% TPP 20 nm/BCP+0.4% Ir(piq)320 nm/Alq3 40 nm/Mg:Ag was fabricated and characterized, where 2,5,7,10-tetra-phenylpyrene and tris(1-phenylisoquinoline) iridium (III) [Ir(piq)3] were used as a blue fluorescent dye and a red phosphorescent dye respectively. The I–V characteristics of the device showed a turn-on voltage of 2.6 V. The electroluminescent spectra of the device consisted of blue fluorescent and red phosphorescent emissions. The intensity of the blue emission increased gradually relative to the red emission with increasing voltage. The emissions of the device were in the white-light region between 10 and 15 V. A maximum white light luminance of 1076 cd/m2 with CIE coordinates of (x, y = 0.27, 0.24) was reached at 15 V with an efficiency of 1.35 cd/A. The white light emission is related to the simultaneous exciton formation on both sides of the TCTA/BCP interface.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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