Silicon interface passivation studied by modulated surface photovoltage spectroscopy

J Dulanto,L Korte,J A Guerra,M A Sevillano-Bendezú,J A Töfflinger,T Dittrich,R Grieseler

doi:10.1088/1742-6596/1841/1/012003

Abstract

We demonstrate that the modulated surface photovoltage spectroscopy (modulated SPS) technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut-off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other methods.

Highlights

Hydrogenated aluminum nitride doped with terbium (AlN:H:Tb3+) has been recently studied for potential applications as a passivating, down-shifting material for silicon solar cells [1]–[4]
The in-phase surface photovoltage (SPV) signals were positive. This means that the modulated charge separation was dominated by drift across an inversion layer in the p-type doped silicon, i.e. a relatively large amount of negative charge was fixed in the AlN:H layers near the interface
For the sample grown with the hydrogen flow of 5 sccm, no SPV signals could be observed without the filter, i.e. the sensitivity was much too low for detecting defect states for this sample

Summary

Introduction

Hydrogenated aluminum nitride doped with terbium (AlN:H:Tb3+) has been recently studied for potential applications as a passivating, down-shifting material for silicon solar cells [1]–[4]. 3. Results and discussion Figure 3 shows the modulated SPV spectra of three AlN:H:Tb3+ layers deposited onto c-Si substrates with different hydrogen flows during deposition (1 sccm, 3 sccm, 5 sccm). For the measurements without the cut-off filter, the maxima of the SPV signals were reached at about 1.35 eV and amounted to about 1 mV, 300 μV and 300 nV for 1, 3 and 5 sccm, respectively.

Results

Conclusion