Post-growth thermal oxidation of wurtzite InN thin films into body-center cubic In2O3 for chemical/gas sensing applications

•Oxidation of h-InN into bcc-In2O3 has been realized at elevated temperatures.•Si3N4 cap improves In2O3 quality obtained by RTA but results in undesired indium.•Cycle-RTA not only improves the quality but also avoids the byproduct of indium.•The oxidation of InN is dominated by oxygen inward diffusion mechanism.•Cycle-RTA tunes the speeds of oxygen diffusion and InN thermal dissociation.

Post-growth thermal oxidations of InN have been studied using high-resolution x-ray diffraction (HRXRD) and secondary ion-mass spectroscopy (SIMS). The InN thin films, having relative high crystal quality, were grown by metal–organic chemical vapor deposition (MOCVD) on c-sapphire substrates using InGaN/GaN buffer layers. HRXRD reveals that oxidation of wurtzite InN into body-center cubic In2O3 occurred at elevated temperatures. A Si3N4 encapsulation improves the crystal quality of In2O3 oxidized by using conventional rapid thermal annealing (RTA) but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profile, using contaminate elements as the ‘interface markers,’ provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. Together with the HRXRD results, we conclude that the crystal quality of the resultant In2O3/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal dissociation, which can be effectively tuned by cycle-RTA. The obtained In2O3/InN heterostructures can be fundamental materials for studying high speed chemical/gas sensing devices.

Graphical abstractOxidation of h-InN into bcc-In2O3 has been realized at elevated temperatures. A Si3N4 cap improves the crystal quality of In2O3 oxidized by conventional RTA but it results in the presence of undesired metallic indium. Cycle-RTA not only improves the crystal quality but also avoids the byproduct of metallic indium. SIMS depth profiles provide evidence that the oxidation of InN is dominated by oxygen inward diffusion mechanism. The crystal quality of the resultant In2O3/InN heterostructure is mainly controlled by the balance between the speeds of oxygen diffusion and InN thermal dissociation, which can be effectively tuned by cycle-RTA.Figure optionsDownload full-size imageDownload as PowerPoint slide