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

5 páginas, 5 figuras.-- PACS: 68.37.Ef; 68.65.Hb; 81.07.Ta.-- Proceedings of the 12th International Conference on Modulated Semiconductor Structures.We present an atomic-scale analysis of the indium 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. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We 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 asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20 nm, which is consistent with the observed electronic radius of QR structures. Based on the structural information from the X-STM measurements, we calculate the magnetization as a function of the applied magnetic field. We conclude that, although the real QR shape differs strongly from an idealized circular-symmetric open ring structure, Aharonov–Bohm-type oscillations in the magnetization can be expected.This work was partially supported by the GOA BOF UA 2000, IUAP, FWO-V projects G.0274.01N, G.0435.03, the WOG WO.025.99N (Belgium), the EC Network of Excellence SANDiE, Contract no. NMP4-CT-2004- 500101 and the EC GROWTH Programme, NANOMAT project G5RD-CT-2001-00545 and NANOSELF project TIC2002-04096-C03-03.Peer reviewe

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

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)