Apparatus and methods are provided. A first apparatus includes: a semiconductor film; and at least one semiconductor nanostructure, including a heterojunction, configured to modulate the conductivity of the semiconductor film by causing photo-generated carriers to transfer into the semiconductor film from the at least one semiconductor nanostructure. A second apparatus includes: a semimetal film; and at least one semiconductor nanostructure, including a heterojunction, configured to generate carrier pairs in the semimetal film via resonant energy transfer, and configured to generate an external electric field for separating the generated carrier pairs in the semimetal film.