Influence of impurities on photocarrier diffusion of high-growth-rate microcrystalline silicon

The ambipolar photocarrier diffusion length, Lamb, observed using the steady-state photocarrier grating technique, has been investigated regarding high-growth-rate microcrystalline Si (μc-Si) together with the lateral size, σL, of grain (column) determined from fractal concepts. Experimental results revealed that the relation between Lamb and σL is linear, and the slope, Lamb/σL, being almost unity or less, indicates intra-grain photocarrier diffusion. Furthermore, after exchanging the aged gas-purifiers for SiH4 and H2 gases to the fresh ones, Lamb was increased for each σL, yielding that the slope, Lamb/σL, was increased from 0.77 to 1.1. In this article, we discuss the effects of impurities, particularly oxygen, on Lamb, in conjunction with the elemental analyses by secondary-ion-microprobe-mass spectrometry.