III-V materials are perfect for photovoltaics applications due to its direct band gap, high absorption, and high carrier mobility. However, III-V materials such as GaAs, InP and other ternary compounds, which are widely used in solar cells, are quite expensive. Meanwhile, silicon solar cells are commercially available and have high enough PCE to compete with III-V cells. Silicon photovoltaics are the most developed at the moment and the theoretical efficiency limit for silicon was already almost reached. For further development of silicon photovoltaics and further improvement of effectivity, it’s obvious to think about a tandem approach and combine silicon with other materials, for instance with III-V. In order to implement tandem solar cell design we growth GaAs nanowires on Si. It’s important to study the epitaxial growth of GaAs nanowires on silicon, its optical and electrical properties, surface passivation of nanowires and contact formation.
In this project, you will be mainly focused on GaAs nanowires growth and in-situ doping by Metal Organic Vapour Phase Epitaxy (MOVPE). High concentration of dopant in nanowires is required to create a high-efficiency tandem solar cell. CBrCl3 is a precursor that allows achieving a high concentration and sharp profile of p-type carbon doping in GaAs thin films. In case of nanowire growth, the in-situ CBrCl3 doping may significantly influence the growth process since Br and Cl byproducts react with Ga. The goal of the project is to investigate this influence of doping and control the doping level in GaAs nanowires.
Your main tasks will be
- GaAs nanowire epitaxial growth by MOVPE
- Scanning Electron Microscopy characterization of the grown nanowires
- Optical and electrical measurements of the doped nanowires
Basic knowledge about fabrication and characterization techniques