Optical properties of GaN nanopillar and nanostripe arrays with embedded InGaN/GaN multi quantum wells

Abstract

GaN nanopillar and nanostripe arrays with embedded InGaN/GaN multi quantum wells (MQWs) were fabricated from planar wafers with different quantum well widths using holographic lithography and subsequent reactive ion etching. Although the etching process led to a reduction in the MQW related luminescence, the etch related damage was successfully healed through annealing in NH 3 /N 2 mixtures under optimized conditions, and the annealed nanopatterned samples exhibited enhanced photoluminescence (PL) compared to the planar wafers. Angular-resolved PL measurements revealed extraction of guided modes from the nanopillar and nanostripe arrays.

Patterned III‐Nitrides on Porous GaN: Extending Elastic Relaxation from the Nano‐ to the Micrometer Scale

“…[ 8 ] Apart from nanowires, nanostripes exhibit uniaxial relaxation perpendicular to the stripe direction, following rules similar to those for nanowires. [ 9–11 ]…”

“…As examples, Figure shows the RSMs of GaN nanopillar and nanostripe arrays with embedded InGaN/GaN multi quantum well (MQW), which were fabricated top down via etching of an initially planar wafer with a coherently strained MQW ( Q x (MQW) = Q x (GaN)). [ 5,11 ] After the planar sample was patterned into pillars, the MQW inside the nanopillars relaxed biaxially adopting the average lattice constant of the MQW, represented by the different Q x value of the MQW peaks compared to the GaN peak in the RSM shown in figure 2d. In the case of the stripe array, the MQW region relaxed perpendicular to the stripe direction (Figure 2e), but remained coherently strained in the direction parallel to the stripe, as indicated by the perfect alignment of the MQW peaks and the GaN peak ( Q x (MQW) = Q x (GaN)) in the RSM shown in Figure 2f.…”

Fabrication and improvement of nanopillar InGaN / GaN light-emitting diodes using nanosphere lithography

“…Thermal annealing, on the other hand, will also affect the interior of the nanopillars and have the possibility of out-diffusing contaminants, and in this regard, it might have been advantageous to thermally anneal at higher temperatures. 13 This was not tested because we wanted to avoid annealing the samples at temperatures similar to or above the epilayer growth temperature. The combination of thermal annealing and HCl treatment is therefore expected to first cure interior damages and diffuse contaminants to the surface, while the HCl treatment thereafter cures the surface.…”

“…There is, however, a greater potential for improved efficiency by etching through the active region to induce strain relaxation and weaken the quantum-confined Stark effect (QCSE). [13][14][15][16][17][18][19][20][21][22] Compared to blue, green InGaN quantum-well structures have a higher strain due to larger lattice mismatch as the InN mole fraction is increased. 23 The strain relaxation effects and the resulting IQE improvement are therefore expected to be higher for long-wavelength quantum-well emitters.…”

“…25 For InGaN∕GaN LED epistructures, the effects of nanostructure size on strain relaxation and photoluminescence (PL) improvement have been investigated using periodic structures. [13][14][15] Various RIE damage-curing techniques have been tested including thermal annealing, 13 KOH to etch damaged side-walls, 15,18,21 and HCl treatment, 17,18 all exhibiting improved PL compared to as-etched samples.…”