Dr. Chang Yang
- Epitaxy, Band Structure Engineering, Heterostructures, Alloying, and Transport Phenomena of Oxide, Nitride and Iodide Thin Films
- Novel p-Type Transparent Conductors
- Novel Photovoltaic Absorbers
- Transparent Electronics
- Transparent Thermoelectrics
- Flexible Electronics
Selected Recent Publications
University of Leipzig
Felix Bloch Institute for Solid State Physics
Dept. of Semiconductor Physics
(Headed by Prof. Dr. Marius Grundmann)
Wurtzite zinc-based oxynitrides as promising photovoltaic absorbers: epitaxy, band-structure engineering and heterostructures
PI: Chang Yang
Funding period: 2017 – 2019
Funding ID: YA 511/1-1
Abstract: This project aims to overcome the fundamental problems of thin film solar cells, such as low cell conversion efficiency as well as technical barriers for the use of non-toxic materials. For this purpose, a new class of unconventional semiconductors with wurtzite structure will be developed by alloying ZnO with III-nitrides (AlN, GaN, InN). Bandgap engineering of such Zn-based oxynitride thin films is achievable by modulating the valence and/or conduction band edges. The substitution of both anion (N on O-site) and cation (Al, Ga and In on Zn-site) allows controllable band structures while ensuring crystallinity. As proof of concept we could reduce the bandgap of ZnO-GaN much below the values of the single compounds. The bandgap would be thereby modulated into the visible light or near-infrared regions (near 1.3 eV) for effective solar-light harvesting. The anticipated goal is tackling the critical problems of Zn-based materials in epitaxial growth and band-structure engineering for photovoltaic application.
Amorphous Thin Films of CuI and CuI-based Alloys
PI: Marius Grundmann, Chang Yang
Funding period: 2019 – 2022
Funding ID: FOR 2857/1, YA 511/2-1
Abstract: This project aims to develop novel p-type transparent amorphous semiconductors based on CuI for transparent flexible electronic applications. The goal is to tackle the problems in amorphization of CuI thin films and to understand the hole transport mechanism of such highly disordered material system, which are the critical issues towards the realization of high-performance transparent flexible devices such as amorphous p-channel thin film transistors.
Open PhD positions
Topics for Bachelor and Master ThesesPlease inquire more details about these topics from Dr. Chang Yang or Prof. Marius Grundmann.
Carrier modulation and structure distortion of CuI by anion doping
Copper iodide (CuI) has been regarded as one of the best transparent p-conductive and thermoelectric materials. The substitution of the monovalent I atoms, e. g. by divalent O, S, Se or Te ions, will allow band structure engineering for control of electrical and thermal transport properties. The structure distortion of zinc-blende CuI will be investigated considering the octahedral configuration of divalent anions, which may induce novel physical phenomena in CuI-based material system.
Electrical and optical properties of (Cu,Ag)I solid solution thin films
Halide compounds such as CuI and AgI are promising semiconductor materials as a result of their superior optoelectrical properties. We have already demonstrated the superior performances of CuI as a p-type transparent conductor and a transparent thermoelectric material. However, semiconducting AgI is scarcely investigated because of its poor air-stability under light. The photodecomposition of AgI could be inhibited in the form of solid solutions. Hence, we will investigate the solid solution of CuI and AgI by co-sputtering technique for improvement of electrical, thermal and also ionic conductivities. Also the band structures of the solid solutions will be investigated for optoelectronic applications.
Sputter deposition of amorphous CuI-based thin films
Transparent amorphous semiconductors (TAS) are key materials in the practical applications of transparent flexible electronics. However, high performance p-type TAS is still an open issue. We will sputter CuI thin films with suitable dopants such as Sn, Al, Ti, Si or Ge. The local coordinations of these dopants are different from the tetrahedral configuration of Cu+ in CuI, possibly leading to suppressed crystallization of zincblende CuI. The transport and mechanic properties of amorphous CuI thin films will be investigated.