III-Nitride Based Visible Single-Photon Sources.

Abstract

Electrons and holes in the QD can occupy only a given set of states with discrete energy levels, such as in an atom. Thus, a QD can act like an atomic two-level system, where the relaxation from an excited state to ground state releases a single photon. Nitride semiconductors, with their wide bandgap and large exciton binding energy have been used as single-photon sources up to room temperature but only through optical excitation. In this work, two different approaches have been investigated for single photon emission: the InGaN/GaN dot-in-nanowire and self-organized quantum dot. InGaN/GaN dot-in-nanowire heterostructures were grown on silicon by molecular beam epitaxy (MBE). Emission from InGaN/GaN dot-in-nanowires can be tuned over the visible spectral range by changing the indium composition. Structural characterization through TEM imaging reveals the nanowires and InGaN quantum dot are free of defects. Optical characterization through temperature dependent photoluminescence (PL) measurements shows high radiative efficiencies of 52% in the blue and 35% in the green emitting dot-in-nanowires. Nanowire p-n junctions containing a single InGaN quantum dot were dispersed on silicon substrates with thermal oxide and used to fabricate single nanowire light emitting diodes (LEDs). Single-photon emission under both optical and electrical excitation excitation was observed from single dot-in-nanowire LEDs. We demonstrate electrically driven single photon emission, with a g(2)(0) = 0.35, from a single InGaN quantum dot emitting in the green spectral range up to 125 K. A detailed study of optical and structural properties of InGaN/GaN dot-in- nanowires shows the formation of self-organized Volmer-Weber dots, with diameters smaller than the nanowire size, in the active region. A planar GaN diode with a single layer of self-organized InGaN/GaN quantum dots was grown on GaN-on-sapphire. These quantum dots, which are 15 nm × 3nm, luminesce in the red spectral range. Single quantum dot light emitting diodes were fabricated and the exciton emission shows single-photon emission with g(2)(0) 0.29 at room temperature. On-demand single-photon emission at an excitation repetition rate of 200 MHz was achieved. Nitride-based high temperature single photon sources have potential applications in quantum cryptography, quantum computation, metrology and other areas.