Open AccessReducing the grain density in semipolar (11-22) AlGaN surfaces on m-plane sapphire substrates
Author(s) -
Humberto M. Foronda,
Sarina Graupeter,
Frank Mehnke,
Johannes Enslin,
Tim Wernicke,
Michael Kneissl
Publication year - 2019
Publication title -
japanese journal of applied physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 129
eISSN - 1347-4065
pISSN - 0021-4922
DOI - 10.7567/1347-4065/ab124d
Subject(s) - materials science , nucleation , sapphire , growth rate , crystal (programming language) , epitaxy , surface roughness , surface finish , grain size , analytical chemistry (journal) , volumetric flow rate , composite material , chemistry , layer (electronics) , optics , thermodynamics , geometry , laser , physics , mathematics , organic chemistry , chromatography , computer science , programming language
The growth mechanisms during metalorganic vapor phase epitaxy (11-22) oriented Al x Ga 1 -x N with x ∼ 0.80 on m-plane sapphire are studied with the intention of mitigating the expansion of misoriented grains, composed of the (1-10-3) crystal orientation and achieving a flat surface with only the (11-22) orientation. An increase in reactor pressure, metalorganic supply, and V/III ratio led to a decrease in the grain density from 1.0 × 10 9 cm −2 to 1.5 × 10 7 cm −2 . By comparing different growth regimes, we found that the main factor suppressing the growth of the (1-10-3) orientation and decreasing the grain density in the AlGaN layers is the growth rate, which decreased with increasing reactor pressure, MO supply, and V/III ratio due to increasing pre-reactions in the gas phase. To mitigate pre-reactions even with lower growth rates, growth conditions with higher total flow and lower TMAl flow were chosen, yielding low growth rates of 0.13 μ m h −1 and a grain density of 3.0 × 10 7 cm −2 at an aluminum mole fraction of 84%. To allow the growth of thick LED heterostructures we demonstrated that such a buffer can be overgrown with higher growth rate AlGaN, yielding a low grain density of 1.0 × 10 6 cm −2 and a smooth morphology with a rms roughness of 2.5 nm by avoiding misoriented crystal propagation during nucleation.