Light can be emitted from a semiconductor material as a result of electron-hole recombination. However, materials capable of emitting such light do not glow at room | Fundamentals of Photonics Bahaa E. A. Saleh Malvin Carl Teich Copyright 1991 John Wiley Sons Inc. ISBN 0-471-83965-5 Hardback 0-471-2-1374-8 E ronfc CHAPTER 16 SEMICONDUCTOR PHOTON SOURCES LIGHT-EMITTING DIODES A. Injection Electroluminescence B. LED Characteristics SEMICONDUCTOR LASER AMPLIFIERS A. Gain B. Pumping C. Heterostructures SEMICONDUCTOR INJECTION LASERS A. Amplification Feedback and Oscillation B. Power C. Spectral Distribution D. Spatial Distribution E. Mode Selection F. Characteristics of Typical Lasers G. Quantum-Well Lasers The operation of semiconductor injection lasers was reported nearly simultaneously in 1962 by independent research teams from General Electric Corporation IBM Corporation and Lincoln Laboratory of the Massachusetts Institute of Technology. 592 Light can be emitted from a semiconductor material as a result of electron-hole recombination. However materials capable of emitting such light do not glow at room temperature because the concentrations of thermally excited electrons and holes are too low to produce discernible radiation. On the other hand an external source of energy can be used to excite electron-hole pairs in sufficient numbers such that they produce large amounts of spontaneous recombination radiation causing the material to glow or luminesce. A convenient way of achieving this is to forward bias a p-n junction which has the effect of injecting electrons and holes into the same region of space the resulting recombination radiation is then called injection electroluminescence. A light-emitting diode LED is a forward-biased p-n junction fabricated from a direct-gap semiconductor material that emits light via injection electroluminescence Fig. a . If the forward voltage is increased beyond a certain value the number of electrons and holes in the junction region can become sufficiently large so that a population inversion is achieved whereupon stimulated emission viz. emission induced by the presence .
