Phosphorus (P) or boron (B) atoms can be doped at temperatures as low as 80 to 350 °C, when crystalline silicon (c-Si) is exposed only for a few minutes to species generated by catalytic cracking reaction of phosphine (PH3) or diborane (B2H6) with heated tungsten (W) catalyzer. This paper is to investigate systematically this novel doping method, “Cat-doping”, in detail. The electrical properties of P or B doped layers are studied by the Van der Pauw method based on the Hall effects measurement. The profiles of P or B atoms in c-Si are observed by secondary ion mass spectrometry mainly from back side of samples to eliminate knock-on effects. It is confirmed that the surface of p-type c-Si is converted to n-type by P Cat-doping at 80 °C, and similarly, that of n-type c-Si is to p-type by B Cat-doping. The doping depth is as shallow as 5 nm or less and the electrically activated doping concentration is 1018 to 1019 cm-3 for both P and B doping. It is also found that the surface potential of c-Si is controlled by the shallow Cat-doping and that the surface recombination velocity of minority carriers in c-Si can be enormously lowered by this potential control.

We improve the passivation property of n-type crystalline silicon (c-Si) surface passivated with a catalytic chemical vapor deposited (Cat-CVD) Si nitride (SiNx) film by inserting a phosphorous (P)-doped layer formed by exposing c-Si surface to P radicals generated by the catalytic cracking of PH3 molecules (Cat-doping). An extremely low surface recombination velocity (SRV) of 2 cm/s can be achieved for 2.5 Ω cm n-type (100) floating-zone Si wafers passivated with SiNx/P Cat-doped layers, both prepared in Cat-CVD systems. Compared with the case of only SiNx passivated layers, SRV decreases from 5 cm/s to 2 cm/s. The decrease in SRV is the result of field effect created by activated P atoms (donors) in a shallow P Cat-doped layer. Annealing process plays an important role in improving the passivation quality of SiNx films. The outstanding results obtained imply that SiNx/P Cat-doped layers can be used as promising passivation layers in high-efficiency n-type c-Si solar cells.

A silicon nitride (SiN x ) single passivation layer, prepared by catalytic chemical vapor deposition (Cat-CVD) and successive annealing, shows high passivation quality on crystalline silicon (c-Si) wafers. Effective minority carrier lifetime (τeff) monotonically increases with increase in deposition substrate temperature (T s) for samples passivated by as-deposited SiN x films, while more significant increase in τeff by annealing tends to be seen for the samples with SiN x films deposited at lower T s. The τeff obtained for the sample deposited at T s of 100 °C and pressure (P) of 10 Pa, after annealing at 350 °C for 30 min in N2, is about 3.0 ms, corresponding to a surface recombination velocity (SRV) of 5.0 cm/s. According to measured H content and fixed charge density (Q f) in the SiN x films, Q f partly contributes to the passivation quality of the films particularly before annealing, while H content plays an important role on improving passivation quality of the films after annealing.