Influence of current conduction paths and native defects on gas sensing properties of polar and non-polar GaN

•CO gas sensing using polar & non-polar epitaxial GaN thin-films is perceived.•Charge carriers emission from a trapped state to a continuum follow Frenkel-Poole model.•SBH increases with temperature while ideality factor and series resistance decreases.•NP–GaN demonstrated a higher shallow and deep level defects as compared to the P–GaN.•The potentiality of NP–GaN over P–GaN films in providing a better sensing characteristics is elaborated.