Utilizing simultaneous Coulomb blockade for electrons and holes in a p-n junction, we can realize a device where a single electron and a single hole are injected into the active region to produce a single photon with well-regulated time interval. The photons emitted from such a device can be studied with single photon counting detectors using a Si solid-state photomultiplier. We report locking of the photon emission with external driving pulse, in the regime where one electron and one hole are injected into the active region on the average. © 1998 IOP Publishing Ltd.