Title:Scanning electron microscope cathodoluminescence of GaN/(Al,Ga)N nanocolumns

Speaker: Dr. U. Jahn (Paul-Drude-Institute Berlin, Germany)

Time: 9:00 AM, Nov. 25, 2008

Venue: Academic meeting center in Institute of Semiconductors, CAS

Abstract:A widely investigated route of the fabrication of nearly strain and defect-free GaN is the growth of GaN nanocolumns by catalyst-free MBE or MOCVD on various substrates including Si. Heterostructures such as quantum wells (QW) have to be integrated into these columns for the application in LEDs. The luminescence distribution of GaN(Al,Ga)N nanocolumns is investigated by spatially and spectrally resolved cathodoluminescence (CL). The optical transition energy of the Qdisks formed in the GaN/(Al,Ga)N nanocolumn structures depends strongly on the diameter of the Qdisks and on the excitation density, indicating the influence of the lateral strain distribution and an effective screening of the internal electrical field within the Qdisks. For thin Qdisks, the strain distribution leads to a separate confinement of electrons and holes at the center and periphery of the thin Qdisks. A sophisticated strain engineering is needed for a high quantum efficiency and narrow optical emission of Qdisk structures.

Dr. Uwe Jahn is a senior scientist at the Paul-Drude-Institute for Solid State Electronics in Berlin, Germany. He got his PhD in 1982 at the Friedrich-Schiller-University Jena, German Democratic Republic. Now his main research field is spatially resolved cathodoluminescence (CL) and photoluminescence of bulk semiconductors and nanostructures. The emphasis of his current activities is investigation and characterization of GaN-related semiconductor layers and nanostructures grown by MBE and MOCVD.