Spatially-resolved optical and structural properties of semi-polar (11-22) Al_xGa_1-xN with x up to 0.56

TY - JOUR

T1 - Spatially-resolved optical and structural properties of semi-polar (11-22) AlxGa1-xN with x up to 0.56

AU - Bruckbauer, Jochen

AU - Li, Zhi

AU - Naresh-Kumar, G.

AU - Warzecha, Monika

AU - Edwards, Paul R.

AU - Jiu, Ling

AU - Gong, Yipin

AU - Bai, Jie

AU - Wang, Tao

AU - Trager-Cowan, Carol

AU - Martin, Robert W.

PY - 2017/9/7

Y1 - 2017/9/7

N2 - Pushing the emission wavelength of efficient ultraviolet (UV) emitters further into the deep-UV requires material with high crystal quality, while also reducing the detrimental effects of built-in electric fields. Crack-free semi-polar (11-22) AlxGa1-xN epilayers with AlN contents up to x=0.56 and high crystal quality were achieved using an overgrowth method employing GaN microrods on m-sapphire. Two dominant emission peaks were identified using cathodoluminescence hyperspectral imaging. The longer wavelength peak originates near and around chevron-shaped features, whose density is greatly increased for higher contents. The emission from the majority of the surface is dominated by the shorter wavelength peak, influenced by the presence of basal-plane stacking faults (BSFs). Due to the overgrowth technique BSFs are bunched up in parallel stripes where the lower wavelength peak is broadened and hence appears slightly redshifted compared with the higher quality regions in-between. Additionally, the density of threading dislocations in these region is one order of magnitude lower compared with areas affected by BSFs as ascertained by electron channelling contrast imaging. Overall, the luminescence properties of semi-polar AlGaN epilayers are strongly influenced by the overgrowth method, which shows that reducing the density of extended defects improves the optical performance of high AlN content AlGaN structures.

AB - Pushing the emission wavelength of efficient ultraviolet (UV) emitters further into the deep-UV requires material with high crystal quality, while also reducing the detrimental effects of built-in electric fields. Crack-free semi-polar (11-22) AlxGa1-xN epilayers with AlN contents up to x=0.56 and high crystal quality were achieved using an overgrowth method employing GaN microrods on m-sapphire. Two dominant emission peaks were identified using cathodoluminescence hyperspectral imaging. The longer wavelength peak originates near and around chevron-shaped features, whose density is greatly increased for higher contents. The emission from the majority of the surface is dominated by the shorter wavelength peak, influenced by the presence of basal-plane stacking faults (BSFs). Due to the overgrowth technique BSFs are bunched up in parallel stripes where the lower wavelength peak is broadened and hence appears slightly redshifted compared with the higher quality regions in-between. Additionally, the density of threading dislocations in these region is one order of magnitude lower compared with areas affected by BSFs as ascertained by electron channelling contrast imaging. Overall, the luminescence properties of semi-polar AlGaN epilayers are strongly influenced by the overgrowth method, which shows that reducing the density of extended defects improves the optical performance of high AlN content AlGaN structures.

KW - emission wavelengths

KW - III-nitride structures

KW - cathodoluminescence

KW - atomic force microscopy

UR - https://www.nature.com/srep/

U2 - 10.1038/s41598-017-10923-9

DO - 10.1038/s41598-017-10923-9

M3 - Article

VL - 7

JO - Scientific Reports

T2 - Scientific Reports

JF - Scientific Reports

SN - 2045-2322

M1 - 10804

ER -