Lateral Composition Modulation in InAs/GaSb Superlattices: Nanometer Sized Quantum Wires Donna W. StokesDMR  The objectives of this research is to understand the structural properties of the nanowires formed by lateral composition modulation (LCM) in InAs/GaSb superlattices (SL) grown on GaSb and AlSb buffer layers with both InSb and GaAs interfacial (IF) layers..  Figure 1 shows a diagram of the 3D structure of the InAs/GaSb nanowire array as seen in a STM image of the sample nm InAs wire-like structures are observed.  An X-ray diffraction reciprocal space map, Fig. 2, and various line scans were used to determine the composition and strain state of the layers. The strain, including the magnitude and sign, and the IF bond type are crucial factors governing the growth of the SL. Our results suggest that it is possible to grow nanowire arrays in semiconductor heterostructures with a small strain.  The strain also has a significant affect on the optical absorption of the system, Fig. 3. For the SL1, with no LCM, typical optical transitions are observed, while for SL2, with LCM, these transitions are smeared. For SL3, with LCM and reduced strain due to growth on an AlSb buffer, the typical transitions as well as additional transitions are observed. These data suggest that that by manipulating the strain state of the SL using various buffer layers, the optical response of the system can be controlled. Fig. 2. X-ray reciprocal space map of the nanowire sample. University of Houston Fig. 1. A reconstructed 3D structure of the InAs/GaSb nanowire array. SL1, No LCM SL2, LCM SL3,LCM reduced strain LH 1 –E 1 HH 1 –E 2 LH 1 –E 2 E 1 –E 2 Fig. 3. Absorption spectra taken in the NIR at 77K of a sample with no LCM, with LCM and with LCM and reduced strain achieved by using a different buffer layer

Education and Outreach:  During the Spring of 2006 semester, approximately 160 Bear Branch Elementary School fifth-graders visited the PI’s laboratory for an informative tour and a demonstration in nanotechnology. See the website anch.html for additional information. anch.html  During the summer 2006 Ross Sterling High School mathematics teacher, Katrina Cushenberry, worked in the PI’s laboratory on a project based on nanoscale technology and how it will affect our future. She was also involved in data collection for a project based on how to improve the math skills of students taking introductory physics courses. Her input on this project was invaluable as it gave first hand information on how the students are prepared mathematically before entering college and how this could be adjusted to help the student be successful in a physics course.  The PI and members of her group also served as judges for the 2006 Houston Engineering and Science Fair in Houston, Texas. Lateral Composition Modulation in InAs/GaSb Superlattices: Nanometer Sized Quantum Wires Donna W. StokesDMR University of Houston Ms. Cushenberry reviews statistical data with Dr. Stokes. Bear Brach Elementary students observed a magnet levitating over a superconductor during a tour of the PI’s laboratory.