Why germanium and silicon are considered as best semiconductors?

actually diamond should be much better, if fabrication issues can be solved, it is faster and will operate up to 600ºC junction temperature. Silicon is limited to 150ºC junction temperature and Germanium is limited to 50ºC to 60ºC. Germanium was originally used because it was easiest to purify and process. Silicon is the cheapest material now, it comes from sand and there is no shortage of that.