The purpose of my thesis is to achieve a demonstrator of a GaAs/Si tandem cell, which has both high efficiency and reasonable cost. The main challenge is to grow these two lattice-mismatched materials without neither dislocations nor antiphase domains. Micrometric crystals have been obtained with the ELTOn method (Epitaxial Lateral overgrowth on Tunnel Oxide from nano-seed). They have an excellent crystal structure and are electrically connected to the silicon substrate by tunnel effect.
Figure 1: Schematic diagram of the lateral growth of GaAs crystal on Si through a thin silica layer
Figure 2 MEB image of GaAs crystals integrated on Si by the process described in Fig1
However, there are other steps to optimize before making a tandem solar cell. One crucial point is to be able to control the doping level of the crystals. That also implies to be able to measure the doping level of a single micrometric crystal. Since they are small, classical characterization methods cannot be used. That is why we developed an indirect analysis method based on the evolution of photoluminescence with temperature. Therefore, we can deduce the type and the concentration of the doping level of a single crystal. With this method, we have shown that the crystal's unintentional p doping due to carbon incorporation could be reduced by increasing the V/III ratio.
Figure 3 : Photoluminescence peaks of GaAs crystals grown by ELTOn with different V/III ratio
04/18 – 09/18 : internship at CEA INES (Institut National de l’Energie Solaire)
Development of dielectric multilayers for homo-junction solar cells, assessment of optical losses :
Optical simulation of anti-reflective coatings, optical and electrical characterization of solar cells
(Spectroscopic ellipsometry, Spectrophotometry, Spectral response, IV curve measurements)
Université Paris Saclay - Master de Sciences Technologies Santé – Mention Energie
Parcours Matériaux, Technologies et Composants : Photovoltaïque – Véhicule électrique (MATEC-PVE)
10 Bd Thomas Gobert
91120 Palaiseau FRANCE
+33 1 70 27 04 88