Enhanced Blue Emission from InGaN Quantum Wells by Surface Plasmon in Multi-Walled Carbon Nanotubes

Abstract

We report on the surface plasmon-mediated blue emission from InGaN/GaN multiple quantum wells (MQWs) with multi-walled carbon nanotubes (MWCNTs). The integrated photoluminescence (PL) intensity from the MQWs with MWCNTs is increased by 2.6 times compared with that of MQWs without MWCNTs. The time-resolved and temperature-dependent PL spectra indicate that the improved PL intensity of MQWs is attributed to an increase in the spontaneous emission rate in the MQWs, which occurred via the coupling of the excitons in the MQWs with surface plasmons in the MWCNTs.Surface plasmon polaritons at metal surfaces and the localized surface plasmons of metal nanoparticles have been extensively studied to enhance the spontaneous emission rate of excitons in multiple quantum wells (MQWs) and the optical output power of light-emitting diodes (LEDs). 1-8 A number of groups have proposed methods to improve the light emission efficiency of quantum well (QW) by controlling the resonance coupling and energy transfer between the QW and surface plasmons (SPs) using metals such as aluminum, 1 gold, 1,7 silver, 4-6 and platinum. 8 Recently, several groups have reported enhanced photoluminescence (PL) of ZnO films 9 and nanowires 10 by SP coupling with carbon nanotubes (CNTs), indicating that CNTs are a feasible source of collective charge oscillations. Furthermore, CNTs have very high electrical conductivity, as well as high thermal conductivity and mechanical strength. However, there have been few studies on the SP coupling of CNTs with InGaN/GaN MQWs which are widely used in GaN-based LEDs.In this study, we report a dramatic increase in the PL emission from InGaN/GaN MQWs at a blue emission wavelength of 465 nm, after the MQWs were spin-coated with multi-walled carbon nanotubes (MWCNTs). Time-resolved and temperature-dependent PL measurements showed that the PL intensity and internal quantum efficiency of the InGaN/GaN MQWs with MWCNTs were enhanced through a resonance coupling between the excitons in the MQWs and SPs in the MWCNTs.The InGaN/GaN MQWs with 465 nm-emission were grown on a c-plane (0001) sapphire substrate using metallorganic chemical vapor deposition. After the growth of a 25 nm-thick GaN nucleation layer at 550 • C, a 2 μm-thick undoped GaN layer and a 2 μm-thick Si-doped n-type GaN layer with a doping level of 4 × 10 18 cm −3 were grown at 1020 • C. Next, five periods of InGaN/GaN QW were subsequently grown at 770 • C to form the MQWs, followed by the formation of a 20 nm-thick undoped GaN layer grown at 970 • C as a spacer-layer between the MQWs and the MWCNTs. The thicknesses of the InGaN QWs and the GaN barriers are 3 and 12 nm, respectively, and the In content in the InGaN QW is 18%. The purified MWCNTs with an average outer diameter of 15.5 nm were sonicated for 24 h in a 1 wt% aqueous solution of sodium-dodecyl-sulfate, to obtain a uniform and stable suspension. Figure 1a and 1b shows high-resolution transmission electron microscopy (HRTEM) images of the purified MWCNTs. The MWCNTs were deposited on the InGaN/GaN M...