X-ray diffraction investigation of a three-dimensional Si/SiGe quantum dot crystal

Abstract

High-resolution x-ray diffraction was employed to study the structural properties of a three-dimensional periodic arrangement of SiGe quantum dots in a Si matrix. Using extreme ultraviolet lithography at a synchrotron source a two-dimensional array of pits ͑period 90ϫ 100 nm 2 ͒ was defined and transferred into a ͑001͒ Si wafer by reactive ion etching. By molecular-beam epitaxy SiGe islands of about 30 nm diameter and 3 nm height were grown into the pits. Subsequent deposition of Si spacer layers of 10 nm thickness and SiGe island layers results in a three-dimensionally periodic arrangement of quantum dots, mediated by the strain fields of the buried dots. Their so far unmatched structural perfection is assessed by coplanar x-ray diffractometry using synchrotron radiation. Reciprocal-space maps around the ͑004͒ and ͑224͒ reciprocal-lattice maps were recorded and analyzed to get quantitative information on the disorder of the dot positions and to obtain the mean Ge content of the dots. In addition, information on the strain fields was deduced from the analysis of the diffraction data. Together with atomic force microscopy data on the island shape and size distribution, a complete structural characterization is achieved.

The thermoelectric properties of Ge/SiGe modulation doped superlattices

“…Therefore, we evaluate the integrated intensity as a function of satellite order and fit it with the corresponding data of our simulations. 38 The result is shown for the centre of the design 1 wafer in Fig. 4.…”

Three-dimensional phononic nanocrystal composed of ordered quantum dots

“…Without the patterned substrate, the dots exhibited random lateral distribution and lower size uniformity, and the wetting layers became thicker compared with those on the patterned regions. 6,12 The results obtained from these random QDs are also shown in Fig. 3 and exhibit a much weaker resonance feature even with thicker wetting layers.…”

“…Sample details can be found elsewhere. 2,6 Arrangement of these QDs composed a nanoscaled cubic crystal with lattice constants of 11 ͑denoted by L͒, 90, and 100 nm. The first step to investigate the consequent phononic band gaps is based on a 3D FDTD method.…”

“…The TEM and x-ray analyses confirmed the periodicities and the 60% Ge content of the SiGe dots. 6 From the AFM images, the height and diameter of the QDs were a͒ Author to whom correspondence should be addressed. Electronic mail: sun@cc.ee.ntu.edu.tw.…”

Formation of long-range ordered quantum dots arrays in amorphous matrix by ion beam irradiation

“…The wave functions of carriers confined in periodically arranged quantum wells may overlap creating minibands of eigenenergies with broad optoelectronical applications. 5 The formation of regularly ordered QDs arrays is usually obtained during the growth of crystalline multilayers ͑MLs͒, 6,7 where the mismatch of the lattice parameters causes elastic forces which induce QDs ordering. Some very recent studies 3,4 showed the possibility of the production of spatially correlated Ge QDs also in amorphous MLs, where the ordering is achieved by the interplay of diffusion and surface morphology mechanisms.…”