11 a.m. July 23, Center of Excellence Symposium hall
Marius Grundman, Leipzig University
"Bipolar oxide electronics - Materials and Devices"
Recent advances in the fabrication of oxide and transparent p-conducting thin films are reported. In conjunction with n-type epitaxial ZnO on Al2O3 and amorphous ZTO (zinc tin oxide) thin films, bipolar diodes with (by far) the highest rectification reported for oxide diodes are presented.
(i) p-type amorphous material derived from ZnCo2O4 spinel (ZCO)
ZCO has been deposited at room temperature using pulsed laser deposition. Hetero pn-diodes have been fabricated with rectification beyond 1010 and are stable for at least a year . JFETs with ZnO channel and p-type a-ZnCo2O4 gate exhibit on/off current ratio larger than 107 and low subthreshold slope of S = 91 mV/dec . Fully amorphous diodes from a-ZCO/a-ZTO exhibit rectification larger than 106 .
(ii) p-type zincblende cuprous iodide (CuI)
CuI is the first reported transparent conductive material . We have fabricated CuI thin films using iodization of copper thin films and direct thermal evaporation . We report epitaxial growth on ZnO(00.1) and NaCl(001). p-CuI/n-ZnO diodes exhibit rectification larger than 106 . We report on transparent photovoltaic cells from p- CuI/n-ZnO hetero-structure diodes . The device physics of type-II band alignment heterojunction diodes is discussed.
(iii) p-type amorphous nickel oxide (NiO)NiO is a well-known p-type oxide. a-NiO/ZnO pn-diodes have been fabricated with rectification beyond 1010, also a diode with type-II band alignment, exhibiting an ideality factor of 2. We report on (semi-)transparent photovoltaic cells from such diodes .