Intensive electroluminescence (EL) visible to the naked eyes is observed from p–i–n structure light emitting diodes with nanocrystalline Si (nc-Si) film as the luminescent layer. It is found the luminescence intensity increases by 20 times compared with that of nc-Si film without p-i-n structure and the turn-on voltage is sharply reduced. Combined with I-V and TEM analysis, the improved EL is attributed to the enhancement of carrier injection probability of nc-Si inserted in p-i-n structure.
A brief history of visible light-emitting diodes (LED's) is given, from the first
experimental observations of H.J.Round in 1907 to the mid-1970's when red and green emitters
were in extensive production. Early investigations were empirical. This was changed with the
invention of the transistor in 1947 by the demonstration of minority carrier injection at a forwardbiased
junction, followed by recombination. In 1952 the discovery of the semiconducting behaviour
of III-V compounds introduced a new range of materials. Gallium nitride seemed attractive for light
emission and was investigated at Philips and RCA laboratories but at the time proved to be too
difficult for practical use. Gallium phosphide emerged as the most promising material and groups to
investigate it were set up at SERL in England, Philips Central Research Laboratories in Germany
and Bell Telephone Laboratories in the USA. Zinc and oxygen doping gave red emission. At
Philips, the emphasis was on efficiencies. At SERL the emphasis was on reproducibility for
manufacturable devices and when the conditions for zinc and oxygen doping were strictly
controlled the world's first practical visible LED's were produced at the end of 1961. At Bell
Telephone Laboratories progress was initially slow but with the advent of liquid-phase epitaxial
growth production of red emitters on the scale required became possible. The accidental discovery
of nitrogen doping of gallium phosphide at Bell led to the production of good green emitters. Until
the end of the 1970's, gallium phosphide red and green emitters dominated the LED market.
Subsequent developments to the present day are sketched in outline.
AbstractIn this paper, the light emission phenomena over solid-state incandescent light emitting devices have been modelled based on Planck's law of blackbody radiation. The emission spectra from the thermal excitation of nano-resistors with and without inclusion of an Indium Tin Oxide (ITO) or amorphous silicon (a-Si) thin film filter is simulated and compared with those measured from actual devices. The simulated emission spectra are further utilized to study the light characteristics for SSI-LED with ITO, a-Si and polycrystalline silicon (poly-Si) thin film filters.
ABSTRACTThe semiconducting-polymer/injecting-electrode heterojunction plays a crucial part in the operation of organic solid state devices. In polymer light-emitting diodes (LEDs), a common fundamental structure employed is Indium-Tin-Oxide/Polymer/Al. However, in order to fabricate efficient devices, alterations to this basic structure have to be carried out. The insertion of thin layers, between the electrodes and the emitting polymer, has been shown to greatly enhance LED performance, although the physical mechanisms underlying this effect remain unclear. Here, we use electro-absorption measurements of the built-in potential to monitor shifts in the barrier height at the electrode/polymer interface. We demonstrate that the main advantage brought about by inter-layers, such as poly(ethylenedioxythiophene)/poly(styrene sulphonic acid) (PEDOT:PSS) at the anode and Ca, LiF and CsF at the cathode, is a marked reduction of the barrier to carrier injection. The electro- absorption results also correlate with the electroluminescent characteristics of the LEDs.
Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes