Foreword to the special issue on polymer light-emitting diodes

Abstract

From the very beginning Philips has participated in inventing, developing and manufacturing semiconductor devices. In consumer electronics silicon, initially discrete, devices rapidly made electron tubes a museum curiosity. Their specific properties and the facility to be scaled down to microscopie dimensions gave rise to the development of integrated circuits and the ensuing redesigned consumer electronics and digital computer applications. Lamps were the initial products that formed, over a century ago, the basis of Philips industrial manufacturing. Today, there is hardly an application oflight for which Philips does not have a product in store. Increasingly electronic circuits are being used in the lighting set-ups and within Philips between these two synergy is not an empty word. An interesting property of semiconductor materials is that they can generate light. In a diode, made of an appropriately chosen semiconductor material and drawing a forward current, the injected electrons and holes may recombine with the emission of light. For physical reasons the material to be used for such light-emitting diodes (LED) is not silicon, but compounds of the much more difficult to handle so-called III-V materials, like GaAs, InP, or combinations of these. The colour of the emitted light depends on the combinations chosen. Philips has been actively engaged in producing such materials and inventing new combinations and manufacturing methods. In all respects Silicon beats III-V compounds and if ever it seems different, that does not last long. Secondly, it is in the nature of a semiconductor diode that it is a small device. Exploiting this facility in the direction of making ever smaller devices has been highly profitable. However, extending in the direction of much larger-areas light-generating devices like displays, would also be highly desirable. The desire to get rid of the bulky structure of a TV tube and to use a flat, thin display has always been there. Less ambitious applications include the type of smaller displays that actually use liquid crystals.