Triethylamine sensing characteristics of nonpolar (11-20) and polar (0001) GaN thin films

Abstract

Intrinsically n-doped a-plane and c-plane GaN thin films were successfully deposited on r-plane and c-plane sapphire substrates, respectively, by metalorganic vapor phase epitaxy (MOVPE). The c-plane GaN sensor shows a response value of 5.23–200 ppm triethylamine (TEA) at 480 °C, much higher than the a-plane one at the same condition. The TEA vapor is detectable down to its threshold value of 1 ppm for the c-plane sensor at 480 °C. Excellent selectivity was obtained for the c-plane sensor, by distinguishing TEA from interfering gases according to a combined signal of response, response time and recovery time. Meanwhile, we investigated pre-adsorption of O2 molecules on the two GaN surface facets using density functional theory (DFT) simulations. The much lower adsorption energy and much more accumulated electrons around the O2 molecules for the c-plane facet explains the above-mentioned better TEA sensing performance of the c-plane sensor as compared to its counterpart.