film formed on the silicon sheets is etched away in an HF, HNO3, CH3COOH mixture. Unsupported sheets at least 5X10 cm in size are currently prepared in the laboratory by this technique with a reasonably high yield if their thickness is equal to or larger than 50 //m (Fig. 11). The perfecting of the ribbon handling expected from a progressive automation of the separation steps, combined with the constant progress in growth control, should ultimately result in a high yield for the preparation of unsupported, thin sheets. Finally, it has been established that the effective minority-carrier diffusion length of the sheets is substantially increased by the separation step [17].
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