Coherent nanocavity structures for enhancement in internal quantum efficiency of III-nitride multiple quantum wells

Abstract

A “coherent” nanocavity structure has been designed on two-dimensional well-ordered InGaN/GaN nanodisk arrays with an emission wavelength in the green spectral region, leading to a massive enhancement in resonance mode in the green spectra region. By means of a cost-effective nanosphere lithography technique, we have fabricated such a structure on an InGaN/GaN multiple quantum well epiwafer and have observed the “coherent” nanocavity effect, which leads to an enhanced spontaneous emission (SE) rate. The enhanced SE rate has been confirmed by time resolved photoluminescence measurements. Due to the coherent nanocavity effect, we have achieved a massive improvement in internal quantum efficiency with a factor of 88, compared with the as-grown sample, which could be significant to bridge the “green gap” in solid-state lighting.

The effects of nanocavity and photonic crystal in InGaN/GaN nanorod LED arrays

“…The improvement of IQE is reasonable for nanorod LEDs, because of the strain relaxation [ 6 – 9 ] and extra in-plane excitonic confinement [ 7 , 10 ] in InGaN active layer. Moreover, the nanocavity effect is confirmed to enhance the spontaneous emission (SpE) rate in well-ordered nanostructures [ 11 , 12 ]. Nevertheless, the emission intensity of nanorod array is improved by an order of magnitude or more, which is mainly due to the reduction of modified guided modes [ 13 – 15 ].…”

“…The propagation modes in the photonic crystal (PhC) do not alter SpE significantly [ 19 ]. On the other hand, the strong coupling of quantized photon modes with quantized excitations in confined photon structure will enhance SpE rate about two orders [ 11 , 12 ]. The blue stimulated emission has been obtained by coupling a specific mode with InGaN active layer in nanocavity [ 24 ].…”

Evaluation of Light Extraction Efficiency of GaN-Based Nanorod Light-Emitting Diodes by Averaging over Source Positions and Polarizations

“…Such optical properties of a nanorod LED structure have been usually studied theoretically using numerical simulations based on the finite-difference time-domain (FDTD) method due to its complex geometry [22][23][24]. In the FDTD method, a point dipole source is placed inside the nanorod structure and the evolution of electromagnetic fields is monitored, from which the LEE or the Purcell factor can be calculated.…”

Monolithically multi-color lasing from an InGaN microdisk on a Si substrate

“…Figure 1a schematically depicts our microdisk laser which is fabricated from the InGaN/GaN MQWs epiwafer. Figure 1a also shows a schematic illustration of our fabrication procedure using a microsphere lithography approach 20 , 21 . Figure 1b shows a cross-sectional scanning electron microscopy (SEM) image of our microdisk, demonstrating straight sidewalls with a thin silicon post underneath which is left to mechanically support the microdisk.…”

“…Figure 4(a) to (c) shows the μ-TRPL decay traces measured as a function of excitation power density at room temperature. A standard bi-exponential model was used to fit the TRPL decay traces when the excitation power density used is below the threshold, and a TRPL trace labelled as I(t) can be described by Equation 2 provided below 19 – 21 : where A 1 and τ 1 (A 2 and τ 2 ) represent the fast (slow) decay components 22 , 23 . Figure 4(a) to (c) also provide the fitting data plotted as green curves, showing that a well-fitting has been obtained using the standard bi-exponential model for the TRPL-decay curves measured when the excitation power density is below the threshold.…”