Al2O3 surface passivation: Electrical characterization using the Quantox tool

It has already been proven that Al
₂
O
₃
can provide a high level of surface passivation for p and n-type crystalline silicon (c-Si). The passivation mechanism is considered to be related to two components: low interfacial trap density (D
_it
) and high amount of negative fixed charges (Q
_f
), which induce a built-in electric field, i.e. field effect passivation. However the surface passivation mechanism is not fully understood yet. In order to get understanding on the electrical parameters and process parameters which govern the passivation quality, a Corona charging tool was employed. This technique enables to bring together spatially resolved information on charges and carrier lifetime. Furthermore, the injection level can be tuned, which allows decoupling the bulk and surface contribution in the carrier lifetime measurement. Two main process parameters: the Al
₂
O
₃
thickness and the post deposition anneal were varied to evaluate the sensitivity of the technique. Interface trap density (D
_it
), flatband voltage (V
_fb
), total amount of charges (Q
_tot
), near surface (NSτ) and bulk lifetime (Bτ) were extracted and compared to Calibrated QSSPC Photoluminescence (QSSPC-PL) measurements. The carrier lifetime information extracted from the “Quantox” shows to be consistent with the one extracted by QSSPC-PL measurements. As a result, the “Quantox” tool appears to be an appropriate tool for solar applications in order to study the quality of any passivation layers and Al
₂
O
₃
in particular.