Advances in light‐emitting diodes

The bright future of semiconductor lamps, especially “light‐emitting diodes,” is by now widely recognized. This recognition is fairly recent even though the existence of light emission from semiconductor junctions has been known for almost twenty years. The transformation of LED's from laboratory devices to commercial products constitutes a good example of the effective interaction between solid‐state materials technology and the quantum theory of condensed matter. Moreover, this interaction continues to generate changes in the materials, fabrication techniques and cost of LED's. In this article we will examine the influence of the fundamental principles of the quantum theory of solids on the design of semiconductor light emitters. Emphasis is placed on some of the more recently recognized consequences of these principles for tunable solid‐state light sources. In particular, we describe how breakdowns of momentum conservation caused by the presence of neutral impurities in semiconductors has exerted a profound influence on the materials used to construct solid‐state lamps.