In light of today's announcement of the 2014 Nobel laureates, and because of a discussion among colleagues about the physical significance of these devices, let me ask:
What is the physical significance of blue LEDs, which challenges had to be overcome to create them? Why are materials with the band gap necessary for blue light apparently so rare/difficult to manufacture?
I know it took decades to create blue LED after Holonyak discovered the first red ones, so there must have been some obstacles, which were maybe also important for other areas of research - otherwise I wouldn't understand why the inventors of the blue LED got a prize that the inventor of the first LED didn't.
Wikipedia has something to say on the topic:
Its development built on critical developments in GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN.
However, I'm asking myself why this is "critical" and why this was difficult.