High brightness GaN based laser diodes (HiBGaN)

Visible LEDs and laser diodes are made of group-III-nitride materials grown by epitaxy methods. They already changed our daily life by their ubiquitous use for illumination and projection. High-power, high-brightness GaN-based lasers could replace discharge light bulbs or low-efficiency laser systems also in large-area display, projection, and other lighting systems as well as in free-space or underwater communication. In order to realize GaN-based lasers with high-brightness the conventional edge emitter design which is based on total interface reflection (TIR) waveguides must be substituted by a vertical mode-expanding waveguide structure. Thereby, a wider optical near-field is achieved resulting in narrower far-field angles of the emission profile. Simultaneously, the mode-expanding waveguide must stabilize the fundamental mode emission by discriminating higher order vertical modes through gain and loss engineering. This NSFC-DFG joint project aims to develop high-power, high-brightness (In,Ga,Al)N laser diodes using the novel photonic band crystal (PBC) laser concept. The principal investigators for this project are Prof. André Strittmatter from the Semiconductor epitaxy department of the Otto-von-Guericke University Magdeburg, Germany (OvGU) and Prof. Tong Cunzhu from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), Chinese Academy of Sciences (CAS), China. Both PI´s have strong background in PBC laser diodes and complementary expertise in simulation, nitride growth and characterization, and device fabrication.
Fundamental research on optimum optical and electrical design of the PBC structure itself and the laser structure in total is necessary. The successful realization of the design crucially depends on the available material combinations in the group-III nitride system. In particular, a materials study regarding mechanical strain, electrical conductivity, and optical losses for the PBC section must be conducted. HiBGaN combines the accumulated, complementary knowledge of both sides by distributing each task to the specific strength of each group. The German side has strong epitaxial growth ability of lattice-matched nitride materials which is prerequisite for thick, low-loss GaN-based PBC designs. OvGU is therefore responsible for the epitaxial growth and characterization of the laser structure. The Chinese side is responsible for design of PBC structures, fabrication and characterization of PBC lasers. Mutual research visits are negotiated to train students, exchange expert knowledge, and initiate long-term partnership between both institutions.