Atom Probe Tomography of Advanced GaN-based LEDs James Speck, University of California-Santa Barbara, DMR 0821168 Atom Probe Tomography 3-D atomic scale chemical maps Sharp tip (pcrepared by FIB or etching) DC E-field + laser pulse (or E-pulse) Atom position via position on detector Atom nature via flight time Atom probe reconstruction: GaN LED Recorded at UCSB on Imago HR 3000 LEAP atom probe m-plane, non-polar LED - 60 million atom data set (left to right) GaN:Si/6X InxGa1-x N/GaN QW/AlyGa1-yN/GaN:Mg Key results Homogeneous InxGa1-x N quantum wells Mg clustering in GaN:Mg layer Color code: Ga+N: green; In: purple; Al: aqua; Mg: red Atom probe data on high performance UCSB m-plane nonpolar GaN-based LEDs (nonpolar orientations of GaN are grown such that the polar c-axis of the wurtzite (hexagonal crystal) is parallel to the film substrate interface – thus avoiding electric polarization in the growth direction Atom probe samples, data, and analysis all performed at UCSB on the Imago HR 3000 LEAP system acquired with the MRI grant. Data shows abrupt interfaces (more details on the next slide) in the InxGa1-x N quantum wells – this addresses a key issue in InxGa1-x N alloys (homogeneous alloys vs. a tendency for clustering) Unexpected Mg clustering in the p-type region (Mg is a the only effective acceptor that generates holes in GaN). Related reference: M. Schmidt et al. JJAP 46, L126 (2007).

Atom Probe Tomography of Advanced GaN-based LEDs James Speck, University of California-Santa Barbara, DMR 0821168 Free surface In: purple; Al: aqua Note that the sample direction is reversed (free surface toward left in this image) Example of detailed information available in high quality atom probe data. This tool, now fully operational, is available ot a broad user base through the open Microscopy and Microanalysis Laboratory in the Materials Department and MRSEC at UCSB Detailed analysis of multiple quantum well (MQW) region Chemically homogeous InxGa1-xN in the quantum wells Abrupt lower and upper interface with additional evidence of floating In layer that leads to additional indium incorporation in barrier layers Broader Impact Example of nanoscale chemical analysis with atomic scale, 3D resolution Unparalleled resolution and dynamic range (from ~1017 cm-3 to bulk composition)

Training Activities James Speck, University of California-Santa Barbara, DMR 0821168 Ravi Shivaraman M.S. in Materials Science (ASU) 1+ year staff member at Imago Scientific Temporary staff member – UCSB Microscopy and Microanalysis Facility (Summer 2009) Ph.D. student – UCSB Materials Department (current) Nicholas Cunningham MS in Mechanical Engineering (UCSB) Ph.D student Summer 2009 LEAP (atom probe) Training Sessions 5 Participants 6 Training Sessions 8 Potential/Current Users This tool, now fully operational, is available ot a broad user base through the open Microscopy and Microanalysis Laboratory in the Materials Department and MRSEC at UCSB. The slide above reflects initial training for new users. 3

International Activities James Speck, University of California-Santa Barbara, DMR 0821168 UCSB-Oxford-Leoben Collaboration Round-robin characterization of a reference advanced high temperature and radiation damage tolerant nano-dispersion-strengthened alloy with far from equilibrium nm scale Y-Ti-O precipitate clusters Excellent agreement between data from three laboratories Example of detailed information available in high quality atom probe data. Collaboration between UCSB (Bob Odette), Oxford (George Smith), and Leoben 4