Wide Bandgap Semiconductors - Defects and Dopants (WEDD) (completed)
This project addresses fundamental issues regarding atomistic phenomena in mono-crystalline zinc oxide (ZnO) and silicon carbide (SiC) - two wide bandgap semiconductors with great promise for renewable energy technology, energy saving (solid state lighting and electrical power distribution) and information technology (sensors and optoelectronics).
About the project
To benefit from the true potential of ZnO and SiC, some critical scientific challenges exist and two of the most crucial ones are tackled here, i.e., controllable and stable doping and electrically active defects. The origin of the commonly observed "inherent" n-type conductivity of as-grown ZnO will be studied in detail and the contributions from intrinsic defects and residual impurities are to be understood and determined quantitatively. An ultimate goal is to master the inherent n-type doping and realize uncompensated high-resistivity samples of device-worthy quality. Tunable and stable p-type doping is the most demanding challenge for a true breakthrough of ZnO-technology in energy saving and optoelectronics. Non-equilibrium processes invoking ion implantation, diffusion and sample quenching are exploited for elements anticipated to have a suitable electronic structure as shallow p-type dopants.
Further, the role of defect species, possibly Zn interstitials, occurring during thermal treatment is to be revealed. 4H-SiC is a prime material for low-loss power electronics and sensors operating in harsh environment but the performance is ultimately limited by deep level defects. Especially, the dominant Z1/2 and EH6/7 centers will be studied regarding identification, suppression and diffusion mechanisms.
The project comprises extensive collaboration with leading international and national research partners.
The primary objectives are:
- to understand and control the inherent n-type doping of mono-crystalline ZnO. Specific objectives include identification and suppression of the prominent "Ec-0.3 eV defect", determination of the role of residual impurities acting as shallow donors and elucidate mechanisms for their removal.
- to accomplish reproducible and stable p-type doping of ZnO via non-equilibrium processes. Especially, elements with suitable electronic structure are evaluated as well as the effect of defect injection during thermal treatment.
- to identify and master deep level defects limiting the performance of SiC-materials and -devices. Specifically, the origin, charge states and pronounced anisotropic diffusion behavior of the dominant "Z1/2" and "EH6/7" centers in 4H-SiC will be unveiled.