Can you create pure semiconductor quantum dots? I have seen composite ones that are created with elements in the group II-VI and III-V. Moreover, it saids that the size of the quantum dots must smaller than the Bohr Excitron Radius. From my understanding of the Bohr Exciton Radius is the distance between the electron and hole encountered in semiconductors. How is it possible for the electron and hole to be a distance greater than that of the material?