A significant improvement in the crystalline quality of GaN has made it possible to produce p-type nitrides and to control the conductivity of n-type nitrides, as well as to produce high-quality quantum structures. These breakthroughs have led to such developments as high-performance short-wavelength photonic devices and high-speed electronic devices. All of these devices are the most environment-friendly ones, they are tough and should enable a tremendous saving in energy. The evolution of nitride semiconductors will have a great impact on the future world. (C) 2002 Elsevier Science B.V. All rights reserved.