S. Ostapenko et al., CHANGE OF MINORITY-CARRIER DIFFUSION LENGTH IN POLYCRYSTALLINE SILICON BY ULTRASOUND TREATMENT, Semiconductor science and technology, 10(11), 1995, pp. 1494-1500
We present a new approach for defect engineering by ultrasound treatme
nt (UST) in solar-grade polycrystalline silicon wafers, leading to sig
nificant enhancement of minority carrier diffusion length (L) in wafer
regions with short L. The maximum value of the UST effect is a 2.7 ti
mes increase of the diffusion length in regions of the sample with L =
10 to 25 mu m. Using the surface photovoltage (SPV) method for non-co
ntact mapping of the diffusion length, we have found both a positive a
nd negative variation of L after UST in different wafer regions. The U
ST effect depends upon temperature, showing an activation energy of ab
out 0.17 eV. A relaxation study of the UST effect shows two different
behaviours: (i) stable result versus post-UST holding time, and (ii) p
artial or complete recovery of the diffusion length. Process (ii) is l
inked to the ultrasound-enhanced dissociation of FeB pairs followed by
pairing kinetics.