NH3 Doping in MOCVD Growth of ZnO Thin Films

In this paper effects of NH3 doping on ZnO thin films grown by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates using diethyl zinc (DEZn) and O2 precursors and N2 as the carrier gas have been studied. NH3 flow rates were varied from 0.1% to 4% in the growth runs. All the runs were done at 500°C at 10 Torr pressure.The XRD measurements show a single ZnO (002) peak. Raman data for the samples confirms presence of ZnO:N modes at 275cm−1, 510cm−1 and 575 cm−1 and 645cm−1. The PL results for Zn rich films show weak broad peaks centered at 480nm and 650nm with no ZnO band edge emission, while oxygen rich films show weak ZnO band edge emission and a strong broad orange peak centered at 650nm. Hall effect measurements indicate that all of the as-grown films are highly resistive. Some are weakly p-type with carrier concentration of 4.24 × 1014 cm−3 and mobility of 16.55 cm2/Vs. Annealing in N2 ambient for 60 minutes at 800°C enhances the PL band edge emission and converts all the films to highly conducting n-type, with carrier concentration on the order of 8 × 1018 cm−3, mobility on the order of 12 cm2/Vs and resistivity of 0.063 Ω-cm.