NER: Engineering of InAs Quantum Dot Ensembles Using Interference of Optical Surface Waves

Suny At Albany, Albany NY

Investigators

Abstract

Engineering of InAs Quantum Dot Ensembles Using Interference of Optical Surface Waves This project addresses the problem of inhomogeneous broadening of the size distribution of quantum dot (QD) epitaxial semiconductor ensembles formed via a stress-driven Volmer-Weber or Stranski-Krastanov growth mechanism. The uniformity and narrow size distribution of the QDs are the major challenges for the utilization of QD structures in optoelectronic devices. The primary goal of this proposal is to evaluate the feasibility of nanoscale control of the nucleation process of InAs QDs on a GaAs surface using the interference of the optical surface waves. The interference pattern will be generated on the surface of the substrate using a pulsed UV laser during the growth of QDs by molecular beam epitaxy (MBE). The pattern, with a typical period of few hundred nm, will be created using two different optical schemes based on: (i) the interference of the incident wave with the scattered coherent surface wave; and (ii) the interference of the incident waves with two surface waves coupled to the split laser beams. The optical interference pattern will modulate periodically the surface properties of the substrate at 100-200 nm level. The nucleation of QDs will be controlled through either substrate temperature modulation, thereby destroying the nucleation clusters in the antinode of the standing wave pattern, or through undulation of the surface by laser ablation to control the surface energy. The 100-nm modulation scale is expected to form a template for initial QD nucleation, and the subsequent evolution of the QD ensemble will be driven thermodynamically towards higher density of dots, (3-10)e10 cm-2. The important features of the in-situ optical impact are that it does not leave any residues on the surface, can be conducted during the growth process, and can be adjusted to introduce the minimum defect density. We will systematically investigate the factors (growth temperature, As flux, growth rate, laser power, etc.) that provide uniform and narrow QD distribution and efficient luminescence. The samples grown using optically controlled nucleation will be studied by the in-situ RHEED, as well as STM, TEM and photoluminescence methods to reveal the correlations between growth parameters, and the structure and properties of the QD systems. The laboratories at the Institute have all the necessary equipment for the QD characterization. This includes state-of-the-art field-emission ultra-high resolution TEM, focused ion beam station, surface analysis tools, five STM tools configured for different imaging modes and environment including ultra-high vacuum, and unique ultrasonic force microscope. The successful completion of the proposed work would have a significant impact on the performance of various optoelectronic components. The method will allow the growth of QD structures with sharp size distribution and high radiative recombination efficiency. For example, the QD structures will be used as active media for laser diodes with superior performance characteristics, such as higher efficiency, higher thermal stability, higher modulation frequency and increased reliability.