I want to confirm (or deny), and expand upon, why I think semiconductors are used in optoelectronic devices rather than conductors. For example, I THINK we use semiconductors in solar cells because they do not automatically re-emit the incident photons they absorb, which is what I THINK would happen if we used a conductor (metal). It seems to me that we are constantly trying to tune the bandgap of semiconductors (via doping, confinement, etc.) to REDUCE the rate of electron-hole recombination and therefore increase the conductivity and reduce (in the case of photovotaics, photocatalysts, etc.) or to INCREASE the rate of recombination (lasers, LEDs). In my mind, we are constantly trying to make semiconductors more like conductors or insulators to serve a specific purpose, rather than just using conductors or insulators. So, what exactly is the point? Is it just because they "absorb" without automatically emitting light? If I recall correctly, many narrow gap SCs do emit light quite quickly.