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Schematic illustrations of the process for fabricating phosphor-free nanopyramid white GaN LEDs by NLP method.
(a) Room-temperature PL spectra from MQWs of nanopyramid LEDs grown on different temperatures, the inset showing the optical microscope image taken from PL measurement. (b) EL emission spectra of the LEDs at a driving current of 20 mA. The inset shows the current–voltage (I-V) characteristic curve and a schematic diagram of current distribution of the nanopyramid LEDs. (c) The sunlight spectra (the data from http://www.nrel.gov/rredc/solar_data.html).
Tilted SEM images of (a) nanopyramid core arrays before MQWs were regrown, (b) nanopyramid LED arrays with SiO2 mask and (c) after removing SiO2, respectively. (d) TEM cross section view of the nanopyramid LED arrays.
(a) High-magnification cross-sectional TEM image of nanopyramid InGaN/GaN MQWs, taken along the [ ], solid arrow indicating the c axis. TEM images of MQWs formed on (b) upper (The inset shows the corresponding diffraction pattern of the nanopyramid LED), and (c) sidewall areas of the nanopyramid LEDs. The MQW thickness (d) and EDX line profiles (e) formed on (c) along the trapezoid QW (the solid straight lines shown the fitting curves). (f) The EDX intensity of MQWs for the scan line perpendicular to the sidewalls and (g) the corresponding EDX peak intensity.
(a) SEM images of a single nanopyramid from the apex (A) to the bottom (M) and (b) the corresponding CL spectrum of every localized position. (c)-(h) Monochromatic CL images at the given emission wavelength.
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