Contactless electroreflectance of GaN bulk crystals grown by ammonothermal method and GaN epilayers grown on these crystals

Room temperature contactless electroreflectance (CER) spectroscopy has been applied to study the energy gap, optical quality, and band bending for n-type and semi-insulating GaN crystals grown by ammonothermal method. Broad CER resonances typical of band-to-band absorption with opposite phases, which indicates opposite band bendings, have been clearly observed for the two types of GaN crystals. In addition, GaN epilayers have been grown by metalorganic chemical vapor deposition on these crystals and characterized by CER spectroscopy. Very narrow CER resonances (∼15 meV), typical of high quality material, have been observed for these epilayers. It confirms the excellent usefulness of ammonothermal GaN substrates for GaN homoepitaxy.