About the project
Fundamental studies of semiconductor physics have provided basic scientific knowledge and lead to life altering technologies. Semiconductors continue to play a leading role in the development of our modem society - with applications ranging from integrated circuits to sensors and energy converting materials like solar cells, light emitting diodes, piezo- and thermoelectric materials.
Zinc Oxide (ZnO) is a promising semiconducting material. It is abundant and non-toxic and can be utilized as a wide band gap semiconductor with potential applications in several fields; as a transparent conductive oxide, thermoelectric material and as ultraviolet light emitting diode, to mention a few. ZnO is regarded as an environmentally safe and biocompatible alternative. To obtain such material properties ZnO is doped by different elements, e.g., n-type (Al, Ga, Si), p-type (Ag, Cu), neutral (Mg) and magnetic active dopants (Ag, Ni, Fe and Cu). However, it has proven to be a challenging material to fully understand and control. Little is known about the diffusion properties, solubility limits and thermal stability of these and other common dopants. There are few available reports on dopant diffusion and solubility and most of them are based on indirect methods (e.g., H, Li, Ga and Al). Furthermore, such knowledge is essential to be able to do controlled and reproducible processing of ZnO in general. E.g., it is not possible at this stage to engineer bulk ZnO with a predefined electrical resistivity.
In this project we will use secondary ion mass spectrometry to study diffusion of common dopants in Zn-/O-rich ambient. Appropriate diffusion models will be developed to describe the mechanisms involved and H and Li will be used as probe elements. The resulting material will be characterized by electrical and optical techniques. From this we will learn more about the dynamic interplay between dopants and intrinsic defects in Zn0 and be able to tailor electrical/optical properties.
Objectives
The primary goal is to understand the dynamic interplay between common dopants and intrinsic defects in ZnO. H and Li will be used in a novel approach as probe elements in combination with diffusion studies in O-/Zn-rich ambient, as measured by SIMS. The ability to understand and control such interactions is decisive for e.g. development of stable p-type ZnO and future applications in optoelectronics, photovoltaics, spintronics etc. The secondary goal is to establish accurate literature values for the diffusivity of several types of dopants in ZnO. The dopants can be divided in n-type (Al, Ga, Si), p-type (Ag, Cu), neutral (Mg) and magnetic active dopants (Ag, Ni, Fe, Cu). Further, clear identification and estimates of absorption strength of H-dopant related vibrational modes as observed by FTIR and identification of dopant related luminescence peaks as observed by PL and DRCLS. The use of EELS will be explored to observe electron energy loss from specific dopants on nanometric scale.