Optical signatures of nitrogen acceptors in ZnO

Abstract

We report on the optical properties of nitrogen acceptor-doped ZnO epilayers in the medium and high doping regimes using temperature and excitation power-dependent, as well as time-resolved photoluminescence experiments. The epilayers were doped with ammonia during homoepitaxial growth on ZnO single-crystal substrates with different surface polarities. Significant differences in the optical characteristics of the epilayers are observed between growth on nonpolar a-plane, polar c-plane Zn-face substrates and polar c-plane O-face substrates, which demonstrates different incorporation of the nitrogen acceptor depending on the substrate polarity. The incorporation of nitrogen into the ZnO films ranges between 10 19 and 10 21 cm −3 as determined by secondary ion mass spectrometry. Within this doping range the samples change from lightly compensated to highly doped compensated. We discuss the unique photoluminescence features of nitrogen-doped ZnO epilayers within the concept of shallow donor-acceptor-pair recombinations and at the highest doping level by the appearance of potential fluctuations.

Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing

“…Nevertheless, a shallow acceptor level has been reported in N-doped ZnO bulk and nanostructures [4,5]. On the basis of a donor-acceptor pair (DAP) recombination at ∼3.24 eV, the binding energy of the acceptor level was determined to be 170 ± 40 meV [4,6,7]. Recent extensive theoretical work, however, shows that N substituting O (N O ) leads to a deep acceptor level of 1.3 eV [8], or 1.6 eV above the valence band [9].…”

Acceptor-modulated optical enhancements and band-gap narrowing in ZnO thin films

“…44 But via an increase in the flow ratio of N 2 , double nitrogen atoms occupy the single oxygen site which results to form double shallow level instead of single deep acceptor. [54][55][56] Optical conductivity of a material is another prime factor which offers vigorous information about band structure of any material. More precisely, it describes the electronic states distribution when optical radiation strikes the surface of the films.…”

Nitrogen and vacancy clusters in ZnO

“…The low temperature was chosen to push the achievable nitrogen concentration into the 10 20 per cm 3 range as the solubility of nitrogen drastically decreases with increasing growth temperature. 8 All films were grown on nonpolar a-plane substrates since the incorporation of unintentional impurities during the CVD process is reduced by using either a-plane or c-plane Zn-face substrates as compared with O-face ZnO, 13,14 and higher nitrogen doping levels can be achieved. 7,8 Bulk ZnO samples were grown by seeded chemical vapor transport (CVT) using ammonia (NH 3 ) as a source of nitrogen dopants.…”

“…8 All films were grown on nonpolar a-plane substrates since the incorporation of unintentional impurities during the CVD process is reduced by using either a-plane or c-plane Zn-face substrates as compared with O-face ZnO, 13,14 and higher nitrogen doping levels can be achieved. 7,8 Bulk ZnO samples were grown by seeded chemical vapor transport (CVT) using ammonia (NH 3 ) as a source of nitrogen dopants. 15 ZnO and graphite powder were loaded into one end of a fused silica ampoule.…”

“…One of the more promising group V dopants for obtaining p-type ZnO is nitrogen, as it should be easily incorporated on the O sublattice thanks to its similar size. Doping through both implantation [4][5][6] and incorporation during growth [7][8][9] are intensively investigated. Positron annihilation spectroscopy is an effective method for the investigation of vacancy-type defects in semiconductors.…”