Electronic Transport through Conical Nanosized GaAs Pillars
- PDF / 4,263,036 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 248 Views
Electronic Transport through Conical Nanosized GaAs Pillars Thorben Bartsch, Christian Heyn, and Wolfgang Hansen Institute for Nanostructure and Solid-State Physics at the University of Hamburg, Jungiusstraße 11, 20355 Hamburg, Germany ABSTRACT We study the electronic transport through epitaxial GaAs nanopillars that are only 16 nm long, with diameters of about 100 nm at the upper and 40 nm at the lower end. The pillars can be considered to be very short conical nanowires embedded in AlGaAs. They represent quantum point contacts between two perfectly lattice matched three-dimensional GaAs charge reservoirs. Distinctive asymmetries are found in the current-voltage characteristics. We associate them with the conical shape of the pillars. Although contact reservoirs and pillars are made from the same material, the transport through the pillars is dominated by tunneling across shallow barriers. This is explained by the quantum size effect on the electronic states within the pillars. INTRODUCTION For nanostructured materials a huge increase of the thermoelectric efficiency is predicted, caused by reduced thermal conductivities and optimized electronic densities of states1-5. In most experimental studies6-9, the large reported efficiency increases are mainly founded on reduced thermal conductivities. Control and optimization of the electronic transport properties caused by quantum confinement effects are still at its infancy4. Thus, model systems like nanowires10,11 or quantum dots12,13 are of high interest for concept studies. A promising model systems are well known quantum point-contacts, defined by gate electrodes in two dimensional electron systems14,15. In these point contacts the gate-voltages adjusts the number of one-dimensional subbands that carry charge current through the contacts. Large thermovoltages are reported, if the onset of a subband crosses the Fermi-energy16,17. Devices studied so far are prepared on bulk substrates, i.e., they are point-contacts only for electrons while for phonons they are bulk systems. Large temperature gradients are not realizable. Here we report about electronic transport studies on nanosized GaAs pillars. These pillars potentially represent point-contacts for electrons, as well as for phonons. A sketch of the investigated structure is shown in figure 1. The pillars have typical lengths of only few nanometers (here 16 nm) and diameters of about 100 nm. They are epitaxially embedded between three-dimensional doped GaAs contact reservoirs on their front and back ends and embedded in an AlGaAs matrix along their circumference. Elsewhere18,19, we realized temperature gradients in the range of 107 K/m along the pillars by removing the AlGaAs matrix. Thereby, the pillars represent ballistic phonon point contacts nearly up to room temperature18-20. Here we will show that the electronic transport through the pillars is similar to the transport through gate-defined quantum point-contacts close to the threshold. So, our pillars are a promising candidate for further thermoelectric investig
Data Loading...
