Growth and characterisation of InAlGaAs quantum wires

In the research of future semiconductor lasers, one important goal is to reduce the dimensionality of the active region - that is to minimise the number of degrees of freedom for the motion of electrons and holes. This will lead to lasers with lower threshold currents, higher differential gain and less temperature dependence.
This project aims at fabricating and optimising one-dimensional semiconductor structures, quantum wires. The structures are grown with molecular beam epitaxy (MBE), using the cleaved edge overgrowth (CEO) technique: First, a number of quantum wells are grown on the [100]-direction, and secondly the quantum wells are cleaved in ultra high vacuum and overgrown with a single quantum well in the [110]-direction. At the T-shaped intersections of two quantum wells a bound quantum wire state is formed, with a typical size of 8 nm ´ 20 nm. The energy difference between the quantum wire state and the lowest quantum well state in the structure, the confinement energy, should be as large as possible to avoid thermal activation out of the quantum wires at room temperature.
A world record confinement energy of 52 meV and the first four-wave mixing study of T-shaped quantum wires have been achieved by the III-V Components Group at COM, using a so-called asymmetric structure in the AlGaAs material system. Future research aims at achieving higher confinement, e.g. by taking advantage of strain effects in the InAlGaAs material system, and laser structures for electrical and optical pumping are being processed. Furthermore, time dependent studies have been initiated, in order to investigate carrier diffusion and capture in the structures.
The fabrication of the quantum wires takes place at the III-V NANOLAB, a collaboration between COM and the NBI at the University of Copenhagen. The wires are characterised at COM, using both photoluminescence as well as more sophisticated techniques like spatially and time resolved photoluminescence and four-wave mixing.