Strain relaxation effect by nanotexturing InGaN/GaN multiple quantum well

Abstract

The relaxation of lattice-mismatched strain by deep postetching was systematically investigated for InGaN/GaN multiple quantum wells ͑MQWs͒. A planar heterojunction wafer, which included an In 0.21 Ga 0.79 N ͑3.2 nm͒/GaN ͑14.8 nm͒ MQW, was etched by inductively coupled plasma dry etching, to fabricate high-density nanopillar, nanostripe, and nanohole arrays. The etching depth was 570 nm for all nanostructures. The diameter of the nanopillars was varied from 50 to 300 nm, then the mesa stripe width of the nanostripes and the diameter of the nanoholes were varied from 100 nm to 440 nm and 50 nm to 310 nm, respectively. The effect of strain relaxation on various optical properties was investigated. For example, in an array of nanopillars with diameter 130 nm and interval 250 nm, a large blueshift in the photoluminescence ͑PL͒ emission peak from 510 nm ͑as-grown͒ to 459 nm occurred at room temperature ͑RT͒. PL internal quantum efficiency ͑defined by the ratio of PL integral intensity at 300 K to that at 4.2 K͒ was enhanced from 34% ͑as-grown͒ to 60%, and the PL decay time at 4.2 K was reduced from 22 ns ͑as-grown͒ to 4.2 ns. These results clearly indicate the reduction of lattice-mismatched strain by postetching, which enhanced strain reduction with decreasing nanopillar diameter down to a diameter of 130 nm, where the strain reduction became saturated. The dependence of RT-PL decay time on nanopillar diameter was measured, and the surface nonradiative recombination velocity was estimated to be 5.8 ϫ 10 2 cm/ s. This relatively slow rate indicates a little etching damage.

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

“…[3][4][5][6][7][8][9][10][11][12] The fabrication method has typically involved "top-down" patterning by etching an initially planar epitaxial structure containing InGaN/GaN QWs, although studies of directly grown nano-columnar structures have also been reported. 12 Correlations between spectroscopic results and numerical simulations of strain relaxation in the QWs were included in the reports by Yu et al 9 and Kawakami et al 10 The authors of Ref.…”

GaN based nanorods for solid state lighting

“…Ramesh et al 119 demonstrated that for the etched GaN nanoLED arrays the emission wavelength had a blueshift from 510 nm for an as-grown layer to 459 nm for top-down GaN nanoLED with a diameter of 51 nm at 300 K (shown in Fig. 23 left).…”

How much better are InGaN/GaN nanodisks than quantum wells—Oscillator strength enhancement and changes in optical properties

“…Unfortunately, a large, strain-induced electric field in III-N heterostructures often severely suppresses the oscillator strength of the exciton and, hence, the radiative decay rate and the internal quantum efficiency (IQE). Since strain is relaxed near free surfaces, nanodisks (NDs) in nanowires, which has a large surfaceto-volume ratio, have been widely considered as a promising solution for improving the IQE of InGaN/GaN photonic devices [4][5][6][7][8][9][10][11] . The accompanying improvement in the radiative decay rate is also important for realizing ultrafast singlephoton sources using InGaN/GaN QDs 3,12 .…”