Paper TF-ThP16
MOCVD Growth of 2-D MgZnO Wurtzite Thin Films for Solar-blind Detector Applications

Thursday, November 13, 2014, 6:00 pm, Room Hall D

We report the MOCVD growth of doped thin 2-D MgZnO films on c-plane sapphire substrates for solar-blind detector applications. Spectroscopic ellipsometry (SE), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to determine the composition. The carrier gas is N₂. For pure ZnO, the precursors are diethylzinc (DEZ) and nitrous oxide (N₂O). When growing p-type material, 3% nitric oxide (NO) in N₂ provides N ions in the +2 oxidation state needed for doping, and growth occurs as a two-step process monitored in real time by the SE. In the first step, we use a low Zn partial pressure to induce V_Zn formation. Because V_Zn energies are low for Fermi levels from mid-gap to the conduction band edge, and because the absorption energy for N_Zn is 0.08 eV for the hexagonal close packed site of the Zn-polar surface, this allows the N to incorporate at Zn sites as N_Zn. In the second step, we use a high Zn partial pressure to drive the formation of oxygen vacancies (V_O). Growth is then followed by an appropriate annealing sequence. While substitutional N on the O sublattice is a deep acceptor, we find that acceptor complexes involving N, H and V_Zn can provide p-type ZnO films with a hole concentration of ~10¹⁸ cm^-3 at room temperature. For MgZnO growth, we use bis-cyclopentadienyl magnesium (BcMg) in addition to DEZ, N₂O, and NO. Although we deposit MgZnO, films of a quality that we consider acceptable have not yet been produced owing to the large parameter space of temperature, precursor flows, and gas pressure.