KAIST

Professor Yong Hoon, Cho (Department of Physics) and his research team synthesized an obelisk nanostructure and successfully formed a single semiconductor quantum exhibiting high reliability to realize an ultra-high speed, highly efficient, release of quantum dots. The result of the research effort was published in the July 5th online edition of Scientific Reports published by Nature. Semiconductor Quantum Dots restrict electrons within a cubic boundary of few nanometers thereby exhibiting similar properties to an atom with discontinuous energy levels. Exploitation of this characteristic makes possible the development of quantum light source, critical for next generation quantum information communication and quantum encryption. High operational temperatures, stability, rapid photon release, electric current capability, and other advantages are reasons why semiconductor quantum dots are regarded as next generation core technology. However conventional, spontaneously formed quantum dots are densely packed in a planar structure rendering the analysis of a single quantum dot difficult and result in the poor efficiency of photon release. In addition, the internal electromagnetic effect which is caused by inter-planar stress results in low internal quantum efficiency due to the difficulty in electron-hole recombination. Professor Cho’s research team synthesized an obelisk shaped nanostructure using nitrides that emit short wavelengths of light. The activation layer was grown on the tip of the nanostructure and the team succeeded in placing a single quantum dot on the nano-tip. The team was therefore able to confirm the ultra-high speed single photon characteristics which occur at low energy levels. Use of unique nanostructures makes synthesis of single atomic structures without processes like patterning while enabling the release of light emitted by the quantum dot. Using this unique method the team showed the increase in internal quantum efficiency. The electromagnetic forces apparent in thin films no longer affects the quantum dot greatly due to the obelisk structure’s reduced inter planar stress. The newly developed quantum light source emits visible light (400nm range) and not the conventional infrared light. This characteristic makes possible it use in communication in free space and enables use of highly efficient, visible range photon detector. Professor Cho commented that “the developed method makes quantum dot growth much easier making single photon synthesis much faster to contribute to the development of practical quantum light source.” And that “the characteristics of the obelisk nanostructure enable the easy detachment from and attachment to other substrates enabling its use in producing single chip quantum light source.” The research was conducted under the supervision of Professor Cho. The researchers werey Jae Hyung, Kim (first author) and Yong Ho, Ko (second author), both Ph.D. candidates at KAIST. The Ministry of Science, ICT and Future Planning, the National Research Foundation, and WCU Program provided support to the research effort.