Real-time metrology of self-assembled epitaxial quantum dots by RHEED

Over recent years self assembled epitaxial quantum dots have gained much interest due to their potential for the development of advanced photovoltaic devices and the ability to control and reproduce desired structural properties of quantum dots (QD´s) during growth is a desirable feature toward exploiting the full potential of these devices. Here and within the context of the archetype InAs/GaAs quantum dot system we provide an in situ approach to the determination of quantum dots size based on calculated reflection high energy electron diffraction (RHEED) patterns. We report the experimental evidence for the existence of periodic intensity fringes along the RHEED chevron tails predicted earlier by the theoretical model. The calculated and observed RHEED intensity profiles are analyzed systematically for different QD heights. The periodicity of the intensity fringes is correlated to the average height of the quantum dots and the possibility of monitoring real time the evolution of dot height during the MBE/CBE growth of self assembled quantum dots is demonstrated. The methodology demonstrated here when combined with the real time RHEED information on the dot surface coverage and facet orientation thus provides a full metrology of self assembled quantum dots that could be in turn used to improve control and reproducibility during growth of quantum dot heterostructures and devices.