Insight into the performance of multi-color InGaN/GaN nanorod light emitting diodes

Abstract

We report on the thorough investigation of light emitting diodes (LEDs) made of core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) in the outer shell, which are grown on patterned substrates by metal-organic vapor phase epitaxy. The multi-bands emission of the LEDs covers nearly the whole visible region, including UV, blue, green, and orange ranges. The intensity of each emission is strongly dependent on the current density, however the LEDs demonstrate a rather low color saturation. Based on transmission electron microscopy data and comparing them with electroluminescence and photoluminescence spectra measured at different excitation powers and temperatures, we could identify the spatial origination of each of the emission bands. We show that their wavelengths and intensities are governed by different thicknesses of the QWs grown on different crystal facets of the NRs as well as corresponding polarization-induced electric fields. Also the InGaN incorporation strongly varies along the NRs, increasing at their tips and corners, which provides the red shift of emission. With increasing the current, the different QW regions are activated successively from the NR tips to the side-walls, resulting in different LED colors. Our findings can be used as a guideline to design effectively emitting multi-color NR-LEDs.

Simultaneous Growth of Various InGaN/GaN Core‐Shell Microstructures for Color Tunable Device Applications

“…The laser and the detector being normal to the surface of the sample, the top facets are easily excited and the light efficiently detected. We previously performed an exhaustive investigation of NR luminescence by different optical techniques which supports this view …”

“…Afterward, the patterned templates were co‐loaded in the MOCVD growth chamber and the GaN regrowth was carried out by pulsed growth at 1050 °C and 200 Torr. The partial pressures of the alternating pulses were 1.3 × 10 4 Pa of ammonia for 10 s and 4.2 Pa of trimethyl‐gallium (TMGa) for 5 s. A dwell time of 1 s was introduced between each pulse and 7.5 × 10 −4 Pa of trimethyl‐silane was added during the TMGa pulse in order to enhance vertical growth …”

“…At low current density, the carriers are injected in the tip of the NRs which emit a faint red color. However, at larger current density, the carriers successively reach the green QWs of the semi‐polar facets and the blue QWs of the sidewalls of the NRs . Since the emission color results from the continuous activation of the QWs on the different facets, the luminescence is broad and the colors, drifting with the current density, are poorly saturated.…”

Indium Localization‐Induced Red, Green, and Blue Emissions of Semipolar (11‐22) GaN‐Based Light‐Emitting Diodes

“…[4,5] Therefore, nonpolar and semipolar GaN thin films have been studied to improve emission efficiency. [4][5][6][7][8][9] In addition, as the indium incorporation rate of the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN film is higher than that of the nonpolar and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GaN films, the semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN is useful for achieving long wavelength (>500 nm) LEDs. [6] Therefore, many research groups have attempted to achieve high-performance green LEDs using semipolar (11)(12)(13)(14)(15)…”

“…[6] Therefore, many research groups have attempted to achieve high-performance green LEDs using semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN films. [7][8][9][10] However, semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN-based LEDs grown on m-plane sapphire still exhibit relative low emission efficiency due to poor crystal properties such as high threading dislocations (%10 10 cm À2 ), basal stacking faults (BSFs) (%10 5 cm À1 ), and arrowhead-like surface structures. [9,10] These crystal defects can affect indium incorporation in the InGaN active layer, [11,12] resulting in a significant broadening and band-filling effect of the emission spectrum.…”