Effect of rapid thermal annealing on polycrystalline InGaN thin films deposited on fused silica substrates

• Polycrystalline InGaN films were deposited on fused silica substrates.
• Rapid thermal annealing effect on structural, electrical and optical properties studied.
• Films' resistivity significantly reduced after annealing at 550 °C, in all InN content cases.
• In higher indium content films, optical band gap blueshifts upon annealing, due to Burstein–Moss effect.
• Photoluminescence emission position was unaffected by the band gap shift.

In this work, we report on the effects of Rapid Thermal Annealing (RTA) on the structural, electrical and optical properties of polycrystalline InGaN thin films deposited on amorphous fused silica substrates by molecular beam deposition. Films with 20%, 35% and 50% indium content were grown and subjected to post-deposition RTA treatments. Annealing promoted crystallization in the case of the film with 0.5 InN mole fraction while in the lower indium content cases no apparent effect on the improvement of crystallinity was observed. For RTA temperature above 550 °C, film resistivity was reduced by at least two orders of magnitude due to annealing-induced increased carrier concentration. The optical properties of the films were systematically studied by variable angle spectroscopic ellipsometry. In the highest indium content films, a monotonic optical band gap widening was observed upon annealing, explained by the Burstein–Moss effect. In contrast, photoluminescence peak position was not affected by the resulting Fermi level changes. This is attributed to the different mechanisms between optical absorption and emission in such highly doped semiconductors.