Nanostructuring of novel semiconductors by ion beams (NanoSiB)

The NanoSiB project is examining fundamental issues regarding ion-beam nanostructuring of single-crystalline zinc oxide (ZnO), which is a novel semiconductor with great prospects in application areas such as photovoltaics, photonics and spintronics. The aim is to understand and control the defect evolution in ZnO and ultimately realize p-type doping by ion implantation.

Researchers are studying fundamental issues regarding ion-beam nanostructuring of single-crystalline zinc oxide (ZnO). The most economical way to produce ZnO is by the hydrothermal growth technique (HT) but the downside of the HT method is high concentrations of impurities, mainly Li.

The use of ion beams in semiconductor science and technology has been a success story since the early 1960s for controlled doping, and currently, we are entering a new exciting era where ion beams are being used for nanostructuring of materials. This approach takes advantage of the inherent dimensions of ion-induced atomic collision cascades (typically, from a few nm to ~1000 nm). The first results in the project show that ion implantation induces small clusters of zinc vacancies which grow in size upon annealing at temperatures above 600 C. These ‘big’ clusters, containing at least 3-4 zinc vacancies, are stable up to 1000 C and they are observed to getter detrimental impurities, like Li, in the ZnO crystal.

The principal goal of the effort is to modify electrical, optical and magnetic properties of single-crystalline thin film and bulk ZnO by nano-scale defect engineering using energetic ion beams. A main subgoal is to understand and control the role of vacancy complexes (especially zinc vacancies) and their interaction with group 1 and V dopant elements and vital impurities like hydrogen and transition metals. Ultimately, ‘tuning’ these vacancy clusters may lead to controllable p-type doping of ZnO by ion implantation.

Among the recent efforts of the group is a study that looks at tuning light absorption by band gap engineering in ZnCdO as a function of MOVPE-synthesis conditions and annealing.

Bengt Svensson, Andrej Kuznetsov