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18 Apr 2005

Volume 86, Issue 16, Articles (16xxxx)

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Electric field-induced transition from heterojunction to bulk charge recombination in bilayer polymer light-emitting diodes

Arne C. Morteani, Peter K. H. Ho, Richard H. Friend, and Carlos Silva

Appl. Phys. Lett. 86, 163501 (2005); http://dx.doi.org/10.1063/1.1899751 (3 pages) | Cited 19 times

Online Publication Date: 12 April 2005

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We investigate the photo- and electroluminescence from bilayers of electron- and hole-transporting polyfluorene derivatives at different device temperatures. We show that barrier-free charge capture at the heterojunction is the sole capture mechanism at low driving voltages (below 2.4×105 V/cm2 at room temperature). In this mechanism, which we suggested recently [ Morteani et al., Adv. Mater. 15, 1708 (2003) ], charge capture produces an interfacial excited state (exciplex) directly and bulk exciton electroluminescence is only achieved through endothermic transfer (activation energy 200 meV) from the exciplex. For high driving voltages (above 8.3×105 V/cm2 at 43 K), however, we find that charges are injected over the heterojunction barriers and subsequent charge recombination occurs in the polymer bulk.
Show PACS
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Efficient polymer white-light-emitting diodes

Yunhua Xu, Junbiao Peng, Yueqi Mo, Qiong Hou, and Yong Cao

Appl. Phys. Lett. 86, 163502 (2005); http://dx.doi.org/10.1063/1.1901824 (3 pages) | Cited 52 times

Online Publication Date: 14 April 2005

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Polymer white-light-emitting diodes (WPLEDs) with bilayer structures were fabricated by the spin-coating method. The device structure used here is indium–tin–oxide/polyethylene dioxythiophene (ITO/PEDOT)/blend1/blend2/Ba/Al, whose blend1 consists of poly(N-vinyl carbazole) (PVK), a copolymer of 9,9-diotylfluorene, and 4,7-di(3-hexyl-thien-2-yl)- 2,1,3-benzothiadiazole (PFO-DHTBT), and blend2 is the blend of polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene) (PFO-poss) and phenyl-substituted PPV derivative (P-PPV). The copolymer PFO-DHTBT emits red light. The blend2 gives off both green and blue emission bands in the electroluminescence (EL) spectrum. The relative intensity of the green and blue bands depends on the blend ratio. The EL spectrum of the device can be controlled by adjusting the weight ratios in the blend1 and blend2, respectively. At the weight ratios of 100:3 (PVK to PFO-DHTBT) in blend1 and 100:1 (PFO-poss to P-PPV) in blend2, and by keeping the thickness of the two blend films to 40 nm, the white fluorescent light emission with CIE coordinates of (0.33, 0.32) is achieved in a large voltage range, the maximal external quantum and luminance efficiencies of 3% (ph/eh) and 4.4 cd/A are obtained at 6.1 V, and the maximal luminance is 6300 cd/m2 at 10 V.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Direct detection effect in small volume hot electron bolometer mixers

J. J. A. Baselmans, A. Baryshev, S. F. Reker, M. Hajenius, J. R. Gao, T. M. Klapwijk, Yu. Vachtomin, S. Maslennikov, S. Antipov, B. Voronov, and G. Gol’tsman

Appl. Phys. Lett. 86, 163503 (2005); http://dx.doi.org/10.1063/1.1887812 (3 pages) | Cited 17 times

Online Publication Date: 14 April 2005

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We measure the direct detection effect in a small volume (0.15 μm×1 μm×3.5 nm) quasioptical NbN phonon cooled hot electron bolometer mixer at 1.6 THz. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300 K and 77 K. Using a 200 GHz bandpass filter at 4.2 K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.40.-x Radiowave and microwave (including millimeter wave) technology
95.55.Rg Photoconductors and bolometers

Fe-implanted InGaAs photoconductive terahertz detectors triggered by 1.56 μm femtosecond optical pulses

Masato Suzuki and Masayoshi Tonouchi

Appl. Phys. Lett. 86, 163504 (2005); http://dx.doi.org/10.1063/1.1901817 (3 pages) | Cited 26 times

Online Publication Date: 15 April 2005

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Performance of InGaAs photoconductive antennas at an excitation wavelength of 1.56 μm has been studied as a terahertz (THz) detector. THz waves in time domain are successfully detected, triggered with 1.56 μm femtosecond optical pulses, owing to Fe implantation and annealing at 400 and 580 °C. The peak amplitudes of the THz detected waves by the as-implanted and the low-temperature-annealed detectors saturate with increasing the excitation power. The thermal annealing affects both the frequency component and the amplitude of the THz detected waveforms. In particular, annealing at 580 °C induces twice the increase in the amplitude of the signals.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.40.Ba Antennas: theory, components and accessories
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
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