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1 Sep 1999

Volume 86, Issue 5, pp. 2373-2926

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Modulation speed of an efficient porous silicon light emitting device

T. I. Cox, A. J. Simons, A. Loni, P. D. J. Calcott, L. T. Canham, M. J. Uren, and K. J. Nash

J. Appl. Phys. 86, 2764 (1999); http://dx.doi.org/10.1063/1.371123 (10 pages) | Cited 7 times

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Trends in the efficiency and small signal modulation behavior of porous silicon light emitting diodes (LEDs) are reported for devices formed by the anodization of bulk silicon p–n junctions. As the average size of the silicon skeleton is decreased, the external electroluminescence (EL) efficiency increases from 0.001% to 0.18% and there is a corresponding blue shift in the EL peak from 776 to 633 nm. An associated tenfold increase is observed in the photoluminescence efficiency while the diode resistance, at 2 V, increases from 3×103 to 1×106 Ω. Under small signal pulsed operation, the voltage dependence of the rising edge of the EL is well described by a carrier mobility of 3×10−4 cm2 s−1 V−1 which is independent of the average size of the luminescent regions of the silicon nanostructure. The falling edge of the EL transient is dominated by radiative recombination of quantum confined excitons. The modulation speed is found to be limited by a combination of carrier mobility in the silicon wires and radiative recombination processes. Evidence of charge trapping and discharge is found in an EL overshoot phenomenon. The major application of this type of porous silicon LED, with modulation speeds below 1 MHz, appears to be for displays integrated with circuitry rather than for optical interconnection.
Show PACS
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Ap Elemental semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
72.20.Ee Mobility edges; hopping transport

Surface energy and polarity of treated indium–tin–oxide anodes for polymer light-emitting diodes studied by contact-angle measurements

J. S. Kim, R. H. Friend, and F. Cacialli

J. Appl. Phys. 86, 2774 (1999); http://dx.doi.org/10.1063/1.371124 (5 pages) | Cited 59 times

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We present contact-angle hysteresis and surface energy of differently treated indium–tin–oxide (ITO) thin films obtained from contact angles for liquids with different polar character. We find that the hysteresis and the polar and dispersion component of the surface energy depend strongly on the surface treatments. Oxygen-plasma treatments induce the highest polarity and the highest total surface energy, and we suggest that this improves the interface formation with polymers, and therefore, the performance of light-emitting diodes. We discuss the results in relation to the ITO surface roughness and chemical heterogeneity modified by the different treatments. © 1999 American Institute of Physics.
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81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
68.03.Cd Surface tension and related phenomena
68.35.Md Surface thermodynamics, surface energies
85.60.Jb Light-emitting devices
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Hd Other semiconductors
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