Optimization of PECVD SiN : H films for silicon solar cells

We have grown silicon nitride (SiN:H) thin films on silicon and glass by th e Plasma Enhanced Chemical Vapor Deposition (PECVD) Method at low temperatu re in order to study their electro-optical properties and correlate these p roperties to the chemical composition of the layers, so that optimum films may be achieved for silicon solar cells. By varying the silane to ammonia r atio in the plasma gas we have been able to modify the index of refraction, the optical band gap and the silicon surface state passivation properties of the films. From this information we have determined that the optimum sil ane to ammonia ratio, with other constant parameters in our system, should be 20/65. Our results indicate that the mid-gap surface state density in si licon can be reduced down to 10(10) cm(-2) eV(-1) when this optimum (silane to ammonia) ratio is used for depositing SiN:H layers. We have confirmed t his optimal ratio by making quantum efficiency measurements on silicon sola r cells having their emitter passivated with SiN:H layers deposited with di fferent silane to ammonia ratios. A great reduction of the surface recombin ation velocity was achieved, as observed from the internal quantum efficien cy measurements, for cells with optimal SiN:H layers as compared to those w ith non-optimum SiN:H layers. (C) 2000 Elsevier Science B.V. All rights res erved.