Summary

Realization of the semiconductor laser diodes (LDs) operating in the blue wavelength region had been a 'dream' for a long time for the scientists working on widegap materials until just a few years ago. Quite remarkable progress has been made in the last few years the dream has come true. The first ZnSe-based blue/green LD was fabricated about four years ago and its officially reported life-time in CW operation exceeds 100 hours now; it is quickly approaching a practical use level. Further, GaN-based blue LDs have also been realized. In this way, the progress in these research fields is quite rapid. The work includes articles on bulk growth, epitaxy, doping and characterization, blue LDs and LEDs, and future prospects in both ZnSe-based and GaN-based areas.