Obtaining a semiconductor with mixed conductivity

[Moreno]

Let say I want to obtain a semiconductor with mixed electron-hole conductivity by doping. Typically it's not going to succeed because donor and acceptor admixtures (electrons and holes) are going to recombine with each other. How can we prevent recombination and preserve mixed conductivity? It is claimed that free electron and a hole (valence electron) cannot recombine if they have aligned spins. Can there be a material in which all the free electrons and holes have aligned spins? Can this state (and mixed conductivity) stay for indefinitely long period of time?

Edited February 7, 2018 by Moreno