Growth of GaAs/AlGaAs nanowires for tandem solar cells on silicon

The NWs were grown on patterned substrates of 0.9 x 0.9 cm2 with a hole network (50 nm in diameter and pitch equal to 500 nm) in a SiO2 mask (the patterning was done at C2N by A. Cattoni and coll.). The choice of Al0.2Ga0.8As as a constituent of the top cell is due to its bang-gap equal to 1.7 eV, which is the optimal value for TSC with a Si bottom cell. The presence of a GaAs core is a neccessary step to bypass the impossibility of growing Al0.2Ga0.8As NWs directly on a Si substrate via the self-catalyzed VLS mechanism. The high vertical NW yields were obtained thanks to a growth procedure including a thermal pre-treatment of the patterned substrates for 15 mn at a temperature 15°C higher than the NW growth temperature.
The as-grown p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs were characterized by Electron Beam Induced Current (EBIC) microscopy at C2N (group of M. Tchernycheva). The current results extremely uniform along 83% of the NW length, thus suggesting the presence of a conformal radial p-i-n junction. I(V) curves measured on single NWs have also revealed a diodic behaviour with very low leakage currents (up to -2V), thus confirming the good quality of the radial p-i-n junction. Such NWs can be therfore considered as potentially well-performing building blocks of the TSC top cell.

Figure legende: (a) GaAs NWs and (b) p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs grown on patterned Si(111) substrates.

Contacts: Michel GENDRY, Alain FAVE

References:

1-Growth optimization and characterization of regular arrays of GaAs/AlGaAs core/shell nanowires for tandem solar cells on silicon
M. Vettori, V. Piazza, A. Cattoni, A. Scaccabarozzi, G. Patriarche, P. Regreny, N. Chauvin, C. Botella, G. Grenet, J. Penuelas, A. Fave, M. Tchernycheva, M. Gendry
Nanotechnology, 30, 084005 (2019)
https://doi.org/10.1088/1361-6528/aaf3fe
2-Nanoscale investigation of radial p-n junction in self-catalyzed GaAs nanowires grown on Si(111)
V. Piazza, M. Vettori, A. Ali, P. Lavenus, F. Bayle, N. Chauvin, F.H. Julien, P. Regreny, G. Patriarche, A. Fave, M. Gendry, M. Tchernycheva
Nanoscale, 10, 20207-20217 (2018) – http://dx.doi.org/10.1039/C8NR03827A

Collaborations:

C2N, A. Cattoni, G. Patriarche and M. Tchernycheva,
IMEP-LAHC, group of A. Kaminski-Cachopo
This work was done in the framework of the HETONAN ANR project and as part of the Marco Vettori PhD thesis.