Modification of semiconductor pref. silicon sheet crystal structure - by zone melting in atmos. contg. oxygen, gives prod. useful in solar cell

摘要

Modification of the crystal structure of a semiconductor esp. in the form of a sheet or strip, involves producing a melt zone in the materials, which extends over the surface from >=1 edge, in an oxidising atmos. and passing the melt zone along the material. The atmos. used should contain >=4 vol.% O2 and pref. is air. Polycrystalline Si can be converted into monocrystalline Si suitable for making solar cells and for other electronic applications reliably and at high throughput and low cost. For 0.25 mm thick sheet, the melt zone can be 2.5 mm or more wide without instability problems if an atmos. contg. O2 is used, of =0.25 mm with an inert atmos. The process can be repeated with the melt zone moving in a different direction. The sheet or strip is moved vertically past a heat source, which pref. is a laser beam vertically past a heat source, which pref. is a laser beam defocussed to the required extent to produce the melt zone.