Search

The stable hydrogen isotope deuterium (D), which is released during the annealing of deuterated silicon nitride films, diffuses through the crystalline silicon and is captured by a thin, amorphous layer of silicon sputtered on the rear surface. We report on the measurement of the concentration of “penetrated” D by secondary ion mass spectrometry to monitor the flux of D diffusing through single-crystalline silicon wafers. The penetrated D content in the trapping layer increases with the annealing time. However, the flux of D injected into the silicon from the silicon nitride layer decreases as annealing time increases.

Defect etching revealed a very large density (similar to 10(9) cm(-2)) of intragrain defects in polycrystalline silicon (pc-Si) layers obtained through aluminum-induced crystallization of amorphous Si and epitaxy. Electron-beam-induced current measurements showed a strong recombination activity at these defects. Cathodoluminescence measurements showed the presence of two deep-level radiative transitions (0.85 and 0.93 eV) with a relative intensity varying from grain to grain. These results indicate that the unexpected quasi-independence on the grain size of the open-circuit voltage of these pc-Si solar cells is due to the presence of numerous electrically active intragrain defects. (c) 2007 American Institute of Physics.

Hydrogenation by high temperature rapid annealing of SiNx:H is found to be very effective on the defects responsible for the carrier trapping effect in multicrystalline silicon. The passivation effect is reversible and is annihilated by a long thermal annealing. As for the passivation of deep, lifetime killing defects, the efficiency of “trap” removal by the short thermal treatment depends on the density of the SiNx:H layer. This effect is, in fact, well correlated with performance improvement observed in solar cells. The parallelism between the trap and recombination center passivation effects suggests that they originate from the same defect.

Heterostructures, such as the crystalline silicon (c-Si)/plasma-enhanced chemical vapor deposited (PECVD) hydrogenated amorphous silicon (a-Si:H) structure, form a possibility in the development of a low recombination rear contact for photovoltaic devices fabricated from p-type c-Si(p) substrates. To find a good compromise between limited charge carrier recombination at the surface and a limited resistivity of the contact, a sandwich structure, such as c-Si(p)∕a-Si:H(i)∕a-Si:H(p+) has been proposed in the past. However, in this letter, we report that whereas a very thin intrinsic a-Si:H layer (∼3nm) may still yield very low values for the surface recombination velocity of low resistivity (0.5–1.5Ωcm) c-Si(p) wafers, the surface passivation properties are lost when this intrinsic film is subsequently covered by a PECVD a-Si:H(p+) layer. This phenomenon suggests that surface recombination does not take place at the c-Si(p)∕a-Si:H(i) interface, but more likely in the defect-rich PECVD a-Si:H(p+) material, by tunneling of minority carriers through the thin a-Si:H(i) layer.