Dynamics of Lithium Incorporation into ZnOLeonard J. Brillson, Ohio State University Research Foundation, DMR 0803276

ZnO is a leading candidate for next generation opto- and microelectronics, yet the ability to dope it p-type remains a decades-old barrier. Depth-resolved cathodo-luminescence spectroscopy (DRCLS) revealed the dynamics by which Li, a leading p-type but amphoteric candidate, incorporates into the ZnO lattice either interstitially (LiI) or substitutionally (LiZn), i.e., as an n-type or p-type dopant, respectively. Annealed and rapidly cooled (1 s) Li-doped ZnO is n-type and low resistivity due to interstitial Li donors, whereas slow cooling (90 s) gives the Li atoms enough time to reach the Zn vacancies to form p-type dopants that compensate Li interstitials and other donors and thus increase resistivity. As the VZn peak decreases, the LiZn feature increases, providing a clear window into the dynamic interplay between point defects and the thermal processing required to control Li diffusion into Zn vacancy sites to promote acceptor doping.

VZn Zn

O

LiI

LiZn

1.8 2.1 2.4 2.7 3.0 3.3102

103

104

High Slow cooled

Quenched0.1ohm* cm

As-grown High

3.0eV

2.1eV

Inte

nsity

(arb

. uni

ts)

Photon Energy (eV)

e- hν

e--e-

h+

LiZn

LiI

Left: DRCL spectra of Li-doped melt-grown ZnO with different thermal treatments. Compared with the 3.3 eV band gap emission, the 2.1 eV Zn vacancy peak (identified previously) decreases dramatically as Li atoms move from interstitial sites to fill the Zn vacancies and a Li-on-Zn-site feature appears at 3.0 eV. Right: DRCLS incident electrons generate an electron cascade (blue), resulting in electron-hole pair generation, recombination, and characteristic defect photon emission (hν).

Columbus School for Girls Summer Internship ProgramLeonard J. Brillson, Ohio State University Research Foundation, DMR 0803276

High school women interns, Adele Anderson, Audrey Coble, Lauren Gerber, Judith Keys, and Grace Bowen following the end-of-summer presentation of their research results. Second row: Ohio State Profs. Umit Ozkan, Leonard Brillson, Stephen Lee, Columbus School for Girls’ science teacher Dr. Kevin Sweeney and Prof. John Lannutti.

Ms. Meghna Srikanth, a rising high school junior, and postdoc Snjezana “Snow” Balaz working in Prof. Brillson’s lab with an ultra high vacuum chamber, glancing incidence electron gun, and monochromator for depth-resolved cathodoluminescence spectroscopy (DRCLS). Audrey and Snow measured the depth distribution of native point defects within the outer few atomic layers of electronic oxide single crystals. These nanoscale measurements revealed a huge sub-surface accumulation of native point defects whose type depended on the crystal’s surface orientation.