Collaborative Research: Synthesis and Investigation of Gallium Nitride Based Quantum Dots

Virginia Commonwealth University, Richmond VA

Investigators

Abstract

The principal investigators propose to study quantum dots (QDs) in the group III-nitride materials system. The objectives are three-fold: 1) to improve the quality of the material by using the dot layers to decouple the active layers of structure from the substrate; 2) to produce a QD laser that has a lower threshold and is more efficient than present nitride lasers; and 3) to produce efficient nitride light emitting diodes (LEDs) that span the electromagnetic spectrum from the blue to the red and that can be made to emit white light. Both of the PIs are carrying out extensive research in the nitrides, and this project will be integral part of their programs. The activity will be largely crystal growth in nature, but work on structure and device processing and materials characterization will also be carried out. Both molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) will be used. This is one of the few projects in the world where both techniques are employed by one research group for the nitrides and will give the researchers the flexibility to choose to best method for each part of the growth process. The PIs propose to produce the dots by two novel techniques which they expect will produce more uniform dots. The first is a crystal growth technique whereby the dot layer is grown pseudomorphically on a nitride layer of smaller lattice constant at low enough temperature so that two dimensional growth occurs. The layer is then annealed to form a layer of self-assembled dots. In the second technique, the growth is stopped just below the dot-forming layer. The sample is then removed from the growth apparatus. It is patterned on a nanoscale with a uniformly spaced array of dimples or hillocks. The sample is then returned to the growth apparatus, and the growth is continued. The pattern serves as a template to form the dots and helps make them more uniform. Partial laser structures will be fabricated from samples made by both methods that will permit the determination of whether the dot size is uniform enough to produce a narrower spontaneous linewidth and, hence, a lower threshold, improved laser. Other characterization measurements, including photoluminescence, cathodoluminescence, atomic force microscopy (AFM), and transmission electron microscopy (TEM) will be carried out. Single color LEDs from blue to red and white LEDs will fabricated and characterized.