"Surface passivation of GaAs nanowires for solar cell application"
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.Project description
In this project, you will be mainly focused on surface passivation of GaAs nanowires. High density of the surface states in unpassivated GaAs creates a lot of traps for carriers and therefore significantly limit overall solar cell efficiency.
The goal of the project is to investigate and compare various passivation methods such as growth of in-situ MOVPE (Metal Organic Vapour Phase Epitaxy) passivation shell; chemical passivation; oxide and nitride passivation deposited by ALD (Atomic Layer Deposition).
Your main tasks will be
- Passivation of the nanowires by various thin film deposition technics
- X-ray photoelectron spectroscopy (XPS) characterization of the passivated structures
- Optical and electrical measurements of the passivated nanowires
Basic knowledge about fabrication and characterization techniques