III-Sb lasers on GaAs using interfacial misfit dislocation arrays

Dr. Ganesh Balakrishnan

Department of Electrical and Computer Engineering,University of New Mexico

In the case of certain highly mismatched semiconductors such as GaSb grown on GaAs the transition from a lattice constant of 5.65 Å to 6.09 Å can be achieved without growing as much as a single mono-layer of GaSb on GaAs. This is realized through the use of certain multi-layer surface reconstructions of Sb on GaAs that form complete planar layers of the Sb-sublattice on the GaAs substrate, thus surpassing the critical thickness for the materials involved. Such a reconstruction results in a periodic 90º-misfit interfacial misfit-dislocation array (IMF) in the Sb layer to accommodate the strain. We have identified through experiments that the (2 x 8) Sb on Ga-terminated GaAs is one such reconstruction that possesses the ability to pack Sb atoms two-dimensionally on the GaAs substrate, in the process forming an array of 90º misfit dislocations. Since these periodic misfit dislocations allow Sb atoms on GaAs to take on the lattice constant of GaSb, the ensuing GaSb growth on such a reconstructed surface is similar to GaSb homoepitaxy. The reconstruction’s ability to self-assemble and dynamically change its coverage on the substrate allows for a monolayer of completely relaxed GaSb to be realized across the entire GaAs substrate. We have realized very high quality IMF layers for growth of GaSb on GaAs. The growth of the III-Sb alloys using the IMF technology has already resulted in the demonstration of electrically injected, room temperature, edge-emitting lasers on GaAs at wavelengths of 1.8 to 2 µm.
This presentation will overview the role of IMF technology in the development of a novel high-power vertical external cavity surface emitting lasers (VECSELs) for Mid-IR operation with an InGaSb QW active region (a0 = 6.09 Å) on a GaAs/AlGaAs distributed bragg reflector (DBR) (a0 = 5.65 Å). A comprehensive look at the factors that affect the residual threading dislocations in such a growth mode will be provided and strategies to achieve sub- 5 x 105 threading dislocations/cm2 will be discussed.

Speaker Biography: Dr. Ganesh Balakrishnan is an Assistant Professor with the ECE department at UNM. Prior to this he was the technical director of the Integrated Nanomaterials Core Group at the California Nanosystems Institute, UCLA. He has a PhD in Optical Sciences from the University of New Mexico, a Masters in Electrical Engineering from the University of Toledo, OH and an Undergraduate degree in Electrical Engineering from the University of Madras, India.

Friday, November 13th at 2:00 pm

Center for High Technology Materials, Room 101

Refreshments will be served at the talk.