Quantum point contact due to Fermi-level pinning and doping profiles in semiconductor nanocolumns

We show that nanoscale doping profiles inside a nanocolumn in combination with Fermi-level pinning at the surface give rise to the formation of a saddle-point in the potential profile. Consequently, the lateral confinement inside the channel varies along the transport direction, yielding an embedded quantum point contact. An analytical estimation of the quantization energies will be given

Untersuchung der Inselbildung im System SiGe/Si

In this work a study on the surface morphology of nominally pure Ge-islands grown on Si-(001)-substrates is presented. The samples were fabricated by low pressure chemical vapour deposition and investigated by scanning electron microscopy and atomic force microscopy. Qualitative and quantitative analyses could be derived from the atomic force micrographs. We were able to observe a clear dependence of the film morphology on substrate temperature. At 700° C a trimodal size distribution appeared, consisting of tiny islands with an average diameter of 33nm, small sized islands of about 150nm and large islands with diameters larger than 500nm. While the size of tiny and small islands remained constant over a wide range of temperatures, the diameter of large islands increased with rising growth temperature. At lowtemperatures (550°C) only tiny islands appear. The results concerning growth morphology can be explained using theoretical models describing nucleation and growth of islands. The island shape seems to be determined preferably by the process of elastic relaxation, while kinetic effects have also to be taken into account. Transmision electron micrographs show that tiny and small islands are elastically relaxed, whereas large islands contain a lot of dislocations. Samples with a silicon cap layer exhibited islands which have become broader and more flat. Photoluminescence measurements were performed with capped samples. The half width of luminescence peaks was found to be determined by the island size distribution and the intensity remained constant in the temperature range from 20K up to 77K

Size distribution and electroluminescence of self-assembled Ge dots

In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small (pyramids) and larger (dome) islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns. (C) 2000 American Institute of Physics. [S0021-8979(00)04610-7]

Bimodal distribution of Ge islands on Si(001) grown by LPCVD

Hut- and dome-shaped islands have been observed during low-pressure vapour phase epitaxy (LPVPE) of Ge on Si(001) at 700 degrees C. The experiments show an island height increase with increasing deposition time (total Ge-coverage was kept constant). The shape transition from huts to domes, which takes place after hut clusters have reached a baselength of 90 nm, indicates that huts are not a stable configuration. The two different island types are found to be the reason for the bimodal nature of the size distribution. Photoluminescence measurements show a linear correlation between hut cluster density and integrated photoluminescence intensity. (C) 2000 Elsevier Science S.A. All rights reserved