A. Augusto

Residual stress and dislocations density in silicon ribbons grown via optical zone melting

We investigate the relationships between growth rate, time-temperature profile, residual stress, dislocation density, and electrical performance of silicon ribbons grown via optical zone melting. The time-temperature profiles of ribbons grown at different velocities were investigated using direct measurements and computational fluid dynamics (CFD) modeling. Residual stresses up to 20 MPa were measured using infrared birefringence imaging. The effect of crystallization speed on dislocation density and residual stress is discussed from the context of thermal stresses during growth. More broadly, we demonstrate the usefulness of combining spatially resolved stress and microstructure measurements with CFD simulations toward optimizing kerfless silicon wafer quality.

First multicrystalline silicon ribbons using the continuous SDS process

This paper reports the first results with both intrinsic and p-doped multicrystalline silicon ribbons obtained by the Continuous Mode Silicon over Dust Substrate process (SDS). The SDS is a two-step process in which the ribbons are obtained directly from a gaseous source, silane. In the first step the pre-ribbon is deposited by continuous optical fast CVD (COFCVD) on top of silicon powder at atmospheric pressure in a range of temperatures of the order of 700 °C. The powder substrate speed was of the order of 10mm/min, and it was subjected to passing several heated zones created by a set of halogen lamps with elliptical mirrors. The pre-ribbon is crystallized by a floating molten zone technique known as Zone Melting Recrystallization (ZMR) to increase crystal quality while avoiding impurity contamination. As deposited, pre-ribbons have a porosity of 25–30%, which drops to zero after crystallization. The crystallized ribbons prepared so far have a typical size of 25 × 80 mm2 and thicknesses below 400μm. The measured effective carrier lifetimes were slightly higher than 3μs, with as grown samples without surface passivation. The crystal grains are typically centimeters long and millimeters wide.

Progress on the continuous optical fast CVD system to grow silicon ribbons for solar cells via SDS process

In this paper we present the progress on the development of the Continuous Optical Fast CVD (COFCVD) system based on the Silicon on Dust Substrate (SDS) process. The SDS process is a ribbon technology [1], where ribbons are grown on top of a silicon dust substrate, directly from a gas precursor, silane. Besides the advantages of avoiding kerf losses, the growth of silicon ribbons directly from a gaseous feedstock has the benefit of bypassing also unnecessary crystallization processes such as the Siemens process (see Figure 1).