Stefan Dauwe

Very low surface recombination velocities on p- and n-type silicon wafers passivated with hydrogenated amorphous silicon films

Outstanding surface passivation of single-crystalline p- as well as n-type silicon is obtained using hydrogenated amorphous silicon (a-Si:H) films deposited at very low temperature in a plasma-enhanced chemical vapor deposition (PECVD) system. It is demonstrated that a-Si:H films with excellent surface passivation properties can be deposited in the temperature range between 200 and 250/spl deg/C. Despite the low deposition temperature, the surface passivation of low-resistivity (/spl sim/1 /spl Omega/cm) p-type silicon provided by the films exceeds that provided by high-temperature (/spl sim/1000/spl deg/C) thermal oxides and PECVD silicon nitride films deposited at temperatures around 400/spl deg/C. A record-low surface recombination velocity (SRV) of 3 cm/s is achieved on 1.6-/spl Omega/cm p-Si. In addition, on 3.4-/spl Omega/cm n-Si wafers, very low SRVs of 7 cm/s are obtained. Investigations regarding the thermal stability of the passivation quality of the a-Si:H films show that the passivation is stable for temperatures exceeding the deposition temperature.

Fixed charge density in silicon nitride films on crystalline silicon surfaces under illumination

A novel method is applied to determine the fixed positive charge density Q/sub f/ in plasma-enhanced chemical vapor deposited silicon nitride (SiN/sub x/) films on crystalline silicon surfaces. In this method, both surfaces of the SiN/sub x/-passivated silicon wafers are charged using a corona chamber and the deposited charge density is measured by means of a Kelvin probe. Subsequently, the carrier lifetime is measured and Q/sub f/ is determined from the dependence of the measured carrier lifetime on the corona charge density. This measurement technique allows us for the first time to determine the crucial parameter Q/sub f/ under illumination. In contrast to previous studies, a very high Q/sub f/ of about 2.3 /spl times/ 10/sup 12/ cm/sup -2/ is found, which is in good correspondence with CV measurements carried out in the dark. Finally, we show that the injection level dependence of the surface recombination velocity is mainly due to recombination in the space charge region at the Si/SiN/sub x/ interface.

Nondestructive Characterization of Voids in Rear Local Contacts of PERC-Type Solar Cells

In this paper, we present two nondestructive characterization methods for the detection of voids in rear local contacts of passivated emitter and rear-type solar cells, namely scanning acoustic microscopy and computer tomography. We compare both methods and include a comparison with electroluminescence measurements. It is shown in this paper that voids can easily be detected with both measurement types without any sample preparation. We found a good match of scanning acoustic microscopy (SAM) and computer tomography (CT), which is presented for this purpose for the first time. The investigation was carried out for different aluminum pastes.