Professor, College of Electronic Science and Technology, Shenzhen University, P.R.China.

Speech Title: Theoretical design of transparent conductors without doping
Abstract: Conventional transparent conductors start from transparent wide-gap insulators and then add doping to induce conductivity. The requirements for dopability by electron (hole) producers are not easy to achieve in many wide-gap materials. Here we propose a concept of intrinsic transparent conductor (ITC) that does not require doping. The ITC is a conductive metallic material that happens to be also transparent. Except doping, ITC shares the other property requirements of conventional TC: (a) acceptable carrier mobility, (b) large energy gap within which there is no optical transition, (c) weak optical transition between the bands on one side of the energy gap, (d) low plasma frequency. We will describe our design principles to search for intrinsic TCs, which guide us to a few groups of candidates ITC materials. (i) The II3-V5-O15 ternary compounds demonstrate n-type conductivity; with Fermi level cutting into a group of energy bands (so being metallic) above which there is a large energy gap. The optical transition across the large energy gap is mostly beyond the frequency of visible light. We find small plasma frequency and weak optical transition between the bands near Fermi level in II3-V5-O15. (ii) In the zincblende structure of I-VI materials, there are intermediate bands (IB’s) with large energy gaps away from the groups of energy bands lying above or below the IB’s. The Fermi level cuts into the intermediate bands. The optical transition between the IB’s and the bands above (or below) is mostly beyond the frequency of visible light. While the optical transition between the IB’s lies in the low frequency range even though the IB’s can have a moderate bandwidth. The intrinsic transparent conductors may open the door to search TC materials among the numerous metallic materials without doping and could offer properties better than conventional transparent conductors due to the lack of defects.