Molecular beam and pulsed laser deposition of ZnS:Cr for intermediate band solar cells

• Cr:ZnS thin films with up to 7.5 at.% Cr, deposited by PLD and MBE are compared.
• The highly doped Cr:ZnS films were made for use in intermediate band solar cells.
• Similar optical properties, but different structural properties were achieved.
• The sub-bandgap absorption increased linearly with Cr concentration.
• Smoother and more textured films were obtained by PLD, compared to MBE.

We have investigated the structural and optical properties of Cr-doped ZnS (ZnS:Cr) thin films (0–7.5 at.% Cr) for use in intermediate band solar cells. The films were grown on Si(100) in molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) equipments. Introducing Cr into ZnS resulted in Cr related sub-bandgap absorption, but also reduced the grain size. The sub-bandgap absorption increased with increasing Cr content, and with increasing growth temperature, but did not depend on the growth method. In contrast, the crystallinity depended strongly on the growth method, and smoother and highly textured films were obtained by PLD. The data indicate that stacking faults are present in all films.