Near field photocurrent spectroscopy of crystalline GaAs solar cells

conference paper

English

Visible Scanning Near Field Optical Microscopy (SNOM) was used to study cleaved edges of GaAs solar cell devices. SNOM is a relatively new technique that combines the versatility of optical microscopy with the resolution of a scanning probe microscope. Light coupled into a tapered optical fiber is used for excitation. The fiber probe is scanned over the sample while being held ~10 nm above the surface. At this point, any number of high resolution (~100 nm) optical measurements can be made. In this work, we measured the NSOM-induced photocurrent in GaAs devices. Our goal was to obtain spatially resolved measurements of the photocurrent response across the various layers in crystalline GaAs solar cells, by studying the cleaved edges of the cells. For excitation energies well above the bandgap, carrier recombination at the cleaved surface had a strong influence on the photocurrent signal. Decreasing the excitation energy, which increased the optical penetration depth, allowed the effects of surface recombination to be separated from collection by the p-n junction. Using this approach, the SNOM measurements directly observed the effects of a buried minority carrier reflector/passivation layer. In conclusion, we have shown that surface recombination has a strong influence on cross sectional SNOM photocurrent measurements of GaAs diodes. Changing the excitation energy allows surface recombination to be separated from collection in the p-n junction. Additionally, we have directly observed the effects of minority carrier reflector layers which are included in solar cells to increase efficiency.

solar cell, crystalline GaAs, local spectroscopy

TOMÁNEK, P.; GRMELA, L.

2004

14. 10. 2004

Vydavatelstvo STU Bratislava

Trnava

80-227-2117-4

CO-MAT-TECH 2004, Proceeding of 12. International Scientific Conference

1365

1370

6