Abstract
Ag coated microgroove with extreme large aspect-ratio of 500:1 was fabricated on p-GaN capping layer to investigate the coupling behavior between quantum wells and surface plasmon in highly spatial resolution. Significant photoluminescence enhancement was observed when the distance between Ag film and QWs was reduced from 220 nm to about 20 nm. A maximum enhancement ratio of 18-fold was achieved at the groove bottom where the surface plasmonic coupling was considered the strongest. Such enhancement ratio was found highly affected by the excitation power density. It also shows high correlation to the internal quantum efficiency as a function of coupling effect and a maximum Purcell Factor of 1.75 was estimated at maximum coupling effect, which matches number calculated independently from the time-resolved photoluminescence measurement. With such Purcell Factor, the efficiency was greatly enhanced and the droop was significantly suppressed.
Highlights
To address the above questions, we investigated the coupling behavior between quantum wells (QWs) and Surface plasmon (SP) in highly spatial resolution to separate the change of light extraction efficiency (LEE) from the total PL emission enhancement
The light emitting diode (LED) sample consists of InGaN/GaN MQWs structures grown on 2 μm GaN on c-plane double side-polished sapphire substrates by metal organic vapor-phase epitaxy (MOVPE)
In order to minimize the LEE change introduced by the geometry of the groove, we etched a very wide microgroove in the p-GaN layer above the QWs by photoresist stamping followed by inductively coupled plasma (ICP) dry etching
Summary
At high current density, by local surface plasmon (LSP) coupling.[15,16] Simulation shows 36% of light enhancement with only 5.2% of efficiency droop at 200 A/cm[2] with a Purcell Factor larger than 2.16–19 direct experimental evidence has yet to be strengthened. To address the above questions, we investigated the coupling behavior between QWs and SP in highly spatial resolution to separate the change of LEE from the total PL emission enhancement. We studied the SP coupling at various temperatures as well as various injection carrier densities. Purcell factor was calculated separately based on IQE and time-resolved photoluminescence (TRPL) measurements. The efficiency as a function of pumping power density with different Purcell factor was measured to show the SP effect on efficiency droop
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