Growth of InAs/GaAs quantum dots covered by GaAsSb in multiple structures studied by reflectance anisotropy spectroscopy

• RA spectra of InAs, GaAsSb and GaAs with surfacting In and Sb atoms are presented.
• Mutual enhancement of In and Sb surfacting atoms were observed by RAS.
• Improved flushing step is suggested for MQD structures with GaAsSb SRL.
• Two flushing steps are recommended for MQD with high Sb concentration in SRL.
• Low growth GaAs spacer rate improves QD formation and MQD structure quality.

In this work we present results obtained on quantum dot (QD) and multiple QD structures with InAs/GaAs QDs covered by GaAsSb strain reducing layer (SRL) prepared by MOVPE. The growth of structures was studied in situ by reflectance anisotropy spectroscopy (RAS), which offers direct observation of processes during the structure growth such as QD formation, and dissolution or surfacting of In and Sb atoms. Enhanced In surfacting was observed for structures with GaAsSb SRL. Possible ways, how to suppress surfacting of both types of atoms and how to prevent their transport on epitaxial surface to the subsequent QD layer in MQD structures, are suggested. Different interruptions, growth rates and temperatures of the separation layer growth are discussed with respect to the suppression of undesired surfacting of In and Sb atoms. The conclusions derived from RAS measurements are supported by HRTEM, AFM or PL results.