±RS a In GaN/GaN MOM Simulated Experiment A 0002 101 00o GaN core O Ga ON Figure 1 InGaN MQW nanowire structures. a, Schematic diagram of an MQw nanowire and magnified cross-sectional view of a nanowire facet highlighting in GaN/ GaN MQW structure. The In GaN layer is indicated in yellow colour. b, Low-resolution TEM image of an MQw nanowire structure. The scale bar is 500 nm. c, High-resolution TEM Corresponding electron diffraction pattern indexed for the [0001] zone axis. d, Dark-field cross-sectional STEM image recorded along the [1120] zone axis of a 26MQw nanowire structure Dashed lines indicate core/shell interface. The scale bar is 100 nm. Inset: Corresponding electron diffraction pattern indexed for the [ 1120] zone axis. e, Left: Schematic Gan wurtzite crystal structure viewed along the [1120] direction. Right: Simulated and experimental CBED patterns along the [1100] zone axis from a 216-nm-thick MQW nanowire cross-sectional sample H-h, Dark-field cross-sectional STEM images recorded along the [1120] direction at the f1101 facet of 3Maw (, 13MQW(g)and 26MQw (h)nanowire structures; scale bars are 20, 50, and 20 nm, respectively ye have exploited cross-sectional TEM imaging of the MQw quantum-well(26MQW) sample( Fig. 1d) highlight several key nanowire structures to visualize directly the quantum-well stacking points. First, analysis of these results shows that epitaxial growth on the nanowire lateral facets. Representative dark-field scanning occurs on the two distinct facet types of the triangular core; TEM(STEM), electron diffraction and energy-dispersive X-ray that is, the two crystallographically equivalent [1101) planes spectroscopy(EDS)data recorded from a 26-period In gan/gan and a (0001) plane, which were determined by the electron naturematerialsIVol7iSeptEmbeR2008Iwww.nature.com/naturematerials 2008 Macmillan Publishers Limited. All rights reservedLETTERS GaN core InGaN/GaN MQW 1120– – – – 1010 0110 1100 〈1120– 〉 0000 [0001] Ga-face N-face Ga N Simulated Experiment 0002 0000 0002– 0002 1101 – GaN core InGaN/GaN MQW (0001) – {1101} – {1101} – GaN GaN InGaN InGaN InGaN GaN a b c d e f g h Figure 1 InGaN MQW nanowire structures. a, Schematic diagram of an MQW nanowire and magnified cross-sectional view of a nanowire facet highlighting InGaN/GaN MQW structure. The InGaN layer is indicated in yellow colour. b, Low-resolution TEM image of an MQW nanowire structure. The scale bar is 500 nm. c, High-resolution TEM image of an MQW nanowire structure taken along the [0001] zone axis. The white arrow indicates the h11¯20i direction (along the nanowire axis). The scale bar is 5 nm. Inset: Corresponding electron diffraction pattern indexed for the [0001] zone axis. d, Dark-field cross-sectional STEM image recorded along the [11¯20] zone axis of a 26MQW nanowire structure. Dashed lines indicate core/shell interface. The scale bar is 100 nm. Inset: Corresponding electron diffraction pattern indexed for the [11¯20] zone axis. e, Left: Schematic GaN wurtzite crystal structure viewed along the [11¯20] direction. Right: Simulated and experimental CBED patterns along the [1 ¯100] zone axis from a 216-nm-thick MQW nanowire cross-sectional sample. f–h, Dark-field cross-sectional STEM images recorded along the [11¯20] direction at the {1 ¯101} facet of 3MQW (f), 13MQW (g) and 26MQW (h) nanowire structures; scale bars are 20, 50, and 20 nm, respectively. We have exploited cross-sectional TEM imaging of the MQW nanowire structures to visualize directly the quantum-well stacking on the nanowire lateral facets. Representative dark-field scanning TEM (STEM), electron diffraction and energy-dispersive X-ray spectroscopy (EDS) data recorded from a 26-period InGaN/GaN quantum-well (26MQW) sample (Fig. 1d) highlight several key points. First, analysis of these results shows that epitaxial growth occurs on the two distinct facet types of the triangular core; that is, the two crystallographically equivalent {1101 ¯ } planes and a {0001} plane, which were determined by the electron 702 nature materials VOL 7 SEPTEMBER 2008 www.nature.com/naturematerials © 2008 Macmillan Publishers Limited. All rights reserved