Single- and dual-variant atomic ordering in GaAsP compositionally graded buffers on GaP and Si substrates

• Published in: Journal of crystal growth 2019-01, Vol.506 (C), p.61-70
• Main Authors: France, R.M., Feifel, M., Belz, J., Beyer, A., Volz, K., Ohlmann, J., Lackner, D., Dimroth, F.
• Format: Article
• Language: English
• Subjects: A1. Defects; A3. Metalorganic vapor phase epitaxy; B2. Semiconducting III–V materials; B3. Solar cells; Buffers; Burgers vector; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; defects; Dislocation density; Gallium phosphides; Gliding; Material properties; MATERIALS SCIENCE; metalorganic vapor phase epitaxy; Nucleation; Phase separation; semiconducting III-V materials; Silicon substrates; solar cells; Surface roughness; Switches; Tellurium; Threading dislocations
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2018.10.007

•CuPtB atomic ordering exists and affects glide energetics in GaAsP graded buffers.•The threading dislocation density rises throughout the buffer from 106 to 107 cm−2.•The TDD is not correlated with glide plane switches, but is with the surface.•Dual variant CuPtB ordering is observed in GaAsP on Si substrates.•Dual- and single- variant ordering have different impacts on dislocation glide. We investigate the material properties of GaAsP graded buffers on both GaP and Si substrates in order to determine limitations to dislocation glide in GaAsP. Phase separation is not observed in these GaAsP buffers, but CuPtB atomic ordering is present, and has an impact on the Burgers vector distribution of gliding dislocations. Tellurium surfactant eliminates ordering in GaAsP, allowing control over the glide plane distribution while highlighting the importance of the growth surface and choice of dopant. The impact of single-variant CuPtB ordering of GaAsP buffers grown on GaP substrates is investigated by monitoring the threading dislocation density throughout the buffer in sequential steps. The dislocation density rises steadily throughout the graded buffer, implying that factors other than ordering-induced glide plane switches play a dominant role in the final dislocation density. We observe an increase in surface roughness throughout the buffer and speculate that a dislocation nucleation source on the surface has a low activation energy and may lead to increased threading dislocation density. On Si substrates, the GaAsP buffer displays dual-variant CuPtB ordering rather than single-variant ordering due to the surface step geometry. We discuss how dual-variant ordering leads to a variable glide force, and thus has a different impact on dislocation dynamics than single-variant ordering. Because the III-V on Si nucleation procedure determines the step geometry, it also influences the dislocation dynamics.