Well, since you obviously can't be bothered to do the research I will tell you. It didn't take them long at all. There were studies looking at the impact of boron-doping and gallium-doping back in the 70s. So why was a patent issued in 2000 that everyone has been waiting to expire? Why hadn't we moved from boron-doped PV substrate to gallium-doped substrate in the two decades between those points? Maybe that is the question you should have been asking.
Turns out that it is incredibly fucking hard to manufacture silicon ingots with the correct doping but without too much oxygen in them that make the gallium-doped wafers perform worse than boron-doped ones. Everyone knew gallium was a better target, no one had a fucking clue how to make them at scale or at an acceptable cost. Figuring this out is ENTIRELY what this patent is about.
Turns out that it is incredibly fucking hard to manufacture silicon ingots with the correct doping but without too much oxygen in them that make the gallium-doped wafers perform worse than boron-doped ones. Everyone knew gallium was a better target, no one had a fucking clue how to make them at scale or at an acceptable cost. Figuring this out is ENTIRELY what this patent is about.