Authors: V.A. Pogrebnyak, E. Akray and A.N. Küçükaltun
Affilation: Cukurova University, Turkey
Pages: 61 - 63
Keywords: quantum well, periodicity, Bragg gap
The study of two-dimensional electronic systems evokes considerable interest due to the broad utilization of the systems in nanotechnology. Design of new devices are commonly based on exploiting the different configurations of multiple-quantum-well (MQW) structures. In these nanostructures, the vertical transport of electrons across quantum wells is commonly used. Despite great progress in this field, a MQW has one main inherent defect: a period of the structure is always greater than a thickness of a single quantum well. Therefore, the electron energy, associated with the period, is always less than the energy of the ground state in the single quantum well. Taking into consideration that the energy level crossing causes important resonance properties of the system, it becomes clear that these resonant properties are excluded from MQW structures using the vertical transport. This defect can be avoided if the in-plane transport of electrons in a quantum well with periodic boundaries is used. In this case there are neither physical nor principal technological restrictions on the relationship between thickness and a period. Modern technology can create lateral nanostructures with a modulation period up to a few nanometers. In this communication, we report the theoretical investigation of the band structure of a periodically corrugated quantum well and experimental modeling of the well by the periodic microwave waveguide. It is shown that the lateral periodic corrugation allows to control totally the in-plane electron transport in such quantum well. For example, the electron transport varies from zero to a maximum value upon a shift of one periodic boundary with respect to another on the half period of the corrugation . This transformation corresponds to metal-insulator transition in the nanostructure that can not be observed in MQW structures using the vertical transport. The metal-insulator transition is caused by the opening of the gap in the energy band diagram of the nanostructure (see Fig.1). The electron properties of the periodic well depend on a ratio between the de Broglie wavelength and characteristic dimensions of the well, therefore, the electron phenomena can be modeled by the periodic waveguide with the same ratio between the parameters. The principal condition of observation of the properties, caused by periodicity in the nanostructure, is l >> a, where l is the electron mean free path, and a is a period of the lateral modulation. The advantage of microwaves in such modeling is the very large “mean free path“ of the electromagnetic wave, almost matching the electron mean free path in superconductors. So the mentioned condition is always met. Fig.2 illustrates the experimental observation of microwave transmission (“metal-insulator transition”) through periodic waveguide at 10.42 GHz. 1. V.A. Pogrebnyak, Physical Review B, vol. 69, No. 24307, 2004, (also in the Virtual Journal of Nanoscale Science & Technology, vol.9, No.25, 2004) Fig.1. Dispersion E(k) for the periodic quantum well. Here, E =E/E1, E1 is the ground electron energy (p=1) in the quantum well, q=2π/a, a is a period of the corrugation. The right side of the graph represents dispersions for the case when the shift ∆x between periodic boundaries is equal to the half period of the corrugation ( ), the left – for the symmetric waveguide ( ). The shift causes the opening of the gap (shaded area) near the bottom of the p=3 2D-subband. Fig.2. The measured transmission through the corrugated waveguide at a fixed frequency of 10.42 GHz (chosen from the gap, shown in Fig.1) is plotted as a function of the phase shift between the two periodic plates. The shift changes transmission from the maximum to zero in accordance with opening of the gap, shown in Fig.1. Dear Organizers, sorry for the large abstract, but it was written in the 1st annoucement about 500 words + graphs. Simply, we have not time to change it just after the opening of this pape.