Electron and hole transport in radial GaSb-InAs nanowire junctions and quantum dots
In this presentation I will discuss recent findings on the electrical properties of GaSb-InAs core-shell nanowires with different core-shell configurations. The heterojunction is a Type II-broken gap, which is of relevance to various device concepts such as tunnel field-effect transistors, but also to fundamental studies of electron-hole interactions.
Radial heterojunctions show gate-controlled ambipolar transport along a wire, where a transition from electron-dominated transport, to hole-dominated transport, is confirmed by studying the sign of a thermoelectric voltage upon applying a heat gradient. Top-gated nanowires, with a pronounced symmetry in the ambipolarity, are also used to demonstrate frequency doubling.
From low temperature studies we find that the band alignment in the heterojunction can be tuned by quantum confinement, and that a transition to a staggered junction occurs for an InAs shell thickness below around 5 nm. Short core-shell segments behave as core-shell quantum dots at low temperatures, where sequential filling of core (hole) states, followed by shell (electron) states is possible going from negative to positive gate voltages. The electrostatic interactions between confined electrons and holes have been studied in core-shell quantum dots having conduction and valence band states that overlap in energy.
We are also investigating the reverse system, with an InAs core and a GaSb shell. Here, the radial (shell) growth can be locally supressed by controlling the InAs crystal phase. Such epitaxially designed core-shell quantum dots, with well-defined InAs wurtzite tunnel barriers, and a zinc-blende quantum dot, provide new possibilities for controlling the dot properties.
Claes Thelander received his M.Sc. and Ph.D. degrees in physics from Lund University, Lund, Sweden, in 1998 and 2003, respectively. In his thesis work, he studied carbon nanotubes and nanoparticles, and developed novel compound nanowire structures for transport studies. During 2006-2008 he joined Qumat Technologies AB and worked on developing field-effect transistors based on compound nanowires. He was an Assistant Project Manager for a large European research program for nanowire electronics (NODE) that ended in 2009. Currently he holds a position as Associate Professor in Nano Physics at Lund University, where he studies the device and transport physics of structures based on In-, Ga-, Sb-, and As-compound nanowires.