Hydrogen and nitrogen incorporation in ZnO thin films grown by radio-frequency (RF) sputtering

Bipolar conduction of electron and holes is mandatory for many electronic and optoelectronic applications of ZnO. Among the impurity atoms suited for acceptor formation nitrogen is the prime candidate. Controlling the incorporation without the formation of deep donors and acceptors and avoiding the deterioration of the materials quality are the main goals for homo- and hetero-epitaxially grown ZnO films. We report on the sputter deposition of N-doped ZnO layers and will show by SIMS and Raman spectroscopy how the substrate type and substrate temperature influence the nitrogen incorporation. Hydrogen in ZnO plays an unusual role since it acts as a shallow donor and may control the n-type conductivity in nominally undoped material. However, it can also be used as an n-type dopant. We will demonstrate this behavior using Hall and optical transmission measurements made on ZnO films prepared by RF-magnetron sputtering. The incorporation of hydrogen as a function of the substrate temperature as well as its thermal stability was investigated by SIMS.