Ordered arrays of arsenic clusters coincided with InAs/GaAs superlattices grown by low-temperature MBE

Abstract

The InAs/GaAs superlattices with up to 30 periods were grown by molecular-beam epitaxy at 200°C. The thickness of the GaAs layers was varied from 20 to 60 nm. The nominal thickness of the InAs layers was either 1 or 0.5 monolayers. High-resolution transmission electron microscopy study revealed indium containing layer to be as thick as 4 monolayer in both cases. This was attributed to the roughness of the growth surface at the low substrate temperature. The concentration of As antisite defects in the as-grown samples was evaluated as (0.5–2)×10 20 cm −3. In spite of such a high concentration of point defects, the X-ray rocking curves were found to be very close to theoretical ones with a large number of interference patterns originated from periodical structure. Upon annealing the excess arsenic precipitated at the InAs delta-layers and in between them. Appropriate annealing conditions were found which allow us to dissolve the clusters in the GaAs spacers and accumulate the majority of clusters in two-dimensional sheets. As a result, artificially ordered superlattices of As cluster sheets were produced.