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

The InAs/GaAs superlattices with up to 30 periods were grown by molecular-b eam epitaxy at 200 degrees C. The thickness of the GaAs layers was varied f rom 20 to 60 nm. The nominal thick ness of the InAs layers was either 1 or 0.5 monolayers. High-resolution transmission electron microscopy study reve aled indium containing layer to be as thick as 4 monolayer in both cases. T his was attributed to the roughness of the growth surface at the low substr ate temperature. The concentration of As antisite defects in the as-grown s amples was evaluated as (0.5-2) x 10(20) cm(-3). In spite of such a high co ncentration of point defects, the X-ray rocking curves were found to be ver y close to theoretical ones with a large number of interference patterns or iginated from periodical structure. Upon annealing the excess arsenic preci pitated 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 p roduced. (C) 1999 Elsevier Science B.V. All rights reserved.