The role of surface kinetics on composition and quality of AlGaN

Metal–polar, Al-rich AlGaN films were grown on both single crystalline AlN and sapphire substrates. The role of surface morphology and surface kinetics on AlGaN composition is presented. With the reduced dislocation density of the films grown on AlN substrates, atomically smooth bilayer stepped surf...

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Published inJournal of crystal growth Vol. 451; pp. 65 - 71
Main Authors Bryan, Isaac, Bryan, Zachary, Mita, Seiji, Rice, Anthony, Hussey, Lindsay, Shelton, Christopher, Tweedie, James, Maria, Jon-Paul, Collazo, Ramón, Sitar, Zlatko
Format Journal Article
LanguageEnglish
Published Elsevier B.V 01.10.2016
Subjects
A1. Growth models
A1. Surface kinetics
A3. Metalorganic chemical vapor deposition
B1. Nitrides
A1. Growth models
B1. Nitrides
A3. Metalorganic chemical vapor deposition
A1. Surface kinetics
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Summary:Metal–polar, Al-rich AlGaN films were grown on both single crystalline AlN and sapphire substrates. The role of surface morphology and surface kinetics on AlGaN composition is presented. With the reduced dislocation density of the films grown on AlN substrates, atomically smooth bilayer stepped surfaces are achieved with RMS roughness of less than 50pm for a 5×5µm2 AFM scan area. By controlling the surface supersaturation through adjusting the growth rate, a transition from 2D nucleation to step flow was observed. The critical misorientation angle for step-bunching in nominal Al0.70Ga0.30N grown with a growth rate of 600nm/h on AlN substrates was found to be 0.4°. The composition of bilayer stepped AlGaN was strongly dependent on substrate misorientation angle, where a compositional variation by a factor of two for a change in misorientation angle from 0.05 to 0.40° was observed; this is explained by the different surface diffusion lengths of Ga and Al. Step-bunching resulted in strong compositional inhomogeneity as observed by photoluminescence and scanning transmission electron microscopy studies. •A kinetic framework for controlling the surface during AlGaN growth on Al-polar surfaces by MOCVD is developed.•The role of surface morphology and surface kinetics on AlGaN composition is presented.•Apparent phase separation of AlGaN was determined not to be an intrinsic property of AlGaN.
ISSN:0022-0248
1873-5002
DOI:10.1016/j.jcrysgro.2016.06.055