Structural and electrical properties of AlN films deposited using reactive RF magnetron sputtering for solar concentrator application

AlN is an interesting material with some excellent properties like high hardness (>11 GPa), high temperature stability (>2400 °C), good electrical resistivity (>10¹⁰ Ω cm), and good thermal conductivity (>100 W/m K). These properties make it useful in the field of photo voltaic systems. Cooling of solar cells in solar concentrator application is of major concern because high temperature reduces their efficiency. In the present work we deposited AlN coating, with and without an Al interlayer, on various substrates like Si, quartz, and copper using RF magnetron sputtering. Deposition conditions such as Al interlayer (deposition time = 5-20 min), Ar:N₂ ratio (N₂% = 0-75%) and substrate bias (0 and −50 V) were changed in order to study their effect on coating properties. Coating surface roughness increased from 0.05 to 0.15 μm with increase in Al interlayer thickness. The coating thickness decreased from 4.4 to 3.1 μm with increase in N₂ gas % and films grew in (0 0 2) orientation. Films deposited on copper using Al interlayer showed good electrical resistance of ∼10¹³ Ω. Films deposited on copper without Al interlayer showed presence of voids or micro cracks and poor electrical properties. AlN films deposited at −50 V bias show cracking and delamination.