Atomic-scale structure and formation of self-assembled In(Ga)As quantum rings

Abstract

The authors present an at.-scale anal. of the In distribution of self-assembled (In,Ga)As quantum rings (QRs), which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. The size and shape of QRs as obsd. by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as obsd. by at. force microscopy on the surface of un-capped QR structures. The authors show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asym. In-rich crater-like shape with a depression rather than an opening at the center and is responsible for the obsd. electronic properties of QR structures. These quantum craters have an In concn. of .apprx.55% and a diam. of .apprx.20 nm, which is consistent with the obsd. electronic radius of QR structures. Based on the structural information from the X-STM measurements, the authors calc. the magnetization as a function of the applied magnetic field. Although the real QR shape differs strongly from an idealized circular-sym. open ring structure, Aharonov-Bohm-type oscillations in the magnetization can be expected. [on SciFinder (R)