Past Events

Abstract:

ZnO is as much a II-VI semiconductor as it is an oxide material. How it is regarded depends on the point of view and the background of the researcher. We will focus on to the semiconductor perspective.

The merits of its semiconductor status are that its band structure is well understood, epitaxial layers can be grown and being incorporated into more complex layered structures such as quantum wells and quantum discs where bandstructure engineering can be employed. Homoepitaxial growth has become possible due to the recent availability of ZnO substrates of different orientations. However, from the semiconductor perspective p-type doping is still a significant problem, so that the fabrication of all oxide based optoelectronic devices despite the advantageous electronic and excitonic properties of ZnO and its alloys still remains a long term research aim. The p-typing doping issue maybe overcome by growing ZnO based structures on p-type GaN substrates. However, this brings other issues into play such as diffusion and local charges at the GaN-ZnO heterointerface. In the first part of the presentation, we will discuss some of our recent spectroscopic work on homoeptaxial ZnO layers and the fabrication of diodes based on heteroepitaxial GaN/ZnO structures.

There have been suggestions that oxide materials, in particular, ZnO are also of interest for thermoelectric applications due to high figures of merit observed for ZnO:Al. This has motivated us to prepare ZnO/ZnS and n-ZnO/n⁺-ZnO microand nanostructures by artificial structuring and to study their thermoelectric properties systematically in terms of the influence of band structure engineering and interfaces. The experimental results can be qualitatively understood in the framework of network models of the Seebeck coefficient and the electric and thermal conductivity.

Coffee and tea will be served 20 minutes prior to the seminar.