Faculty of Science, Beijing University of Posts and Telecommunications, China

Biography: Dr. Zhenping Wu received his Ph.D. degree in Condensed Matter Physics from the University of Hong Kong (HKU), in 2012. He is currently an Associate Professor in Faculty of Science, Beijing University of Posts and Telecommunications (BUPT). His research interests are in fabrication and optoelectronic characterization based on wide bandgap semiconductors and related oxide heterostructures. Dr. Wu has published ~60 papers indexed by ISI Web of Science.

Speech Title: Tailoring the photoelectric properties of epitaxial β-Ga₂O₃ thin films through lattice mismatch and crystal orientation

Abstract: Realizing manipulation of the photoelectric properties of wide band gap semiconductors is a major challenge for succeeding in the design of a new generation of functional devices recently. As a wide band gap semiconductor, Ga₂O₃ (Eg ~ 4.9 eV) has stimulated enormous research interest, owing to its extraordinary civil and military surveillance applications. Previous studies have indicated that both lattice matching and interfacial stress of the film/substrate can modify the orientation and crystallinity of the high epitaxial films, play an important role to tune their complex properties. Ga₂O₃ is known to have five commonly polymorphs, labeled as α-, β-, γ-, δ-, and ε-phases, in which the most stable phase is the β-phase. β-Ga₂O₃ has a monoclinic crystal structure, with a, b, c, and β values of 1.22 nm, 0.304 nm, 0.58 nm and 103.7°, respectively. Here, we investigated lattice misfit, substrate symmetry, and crystal orientation effects on the photoelectric properties by heteroepitaxial growth of β-Ga₂O₃ thin films on substrates with different symmetries and lattice parameters [(100) MgO, (100) MgAl₂O₄ and (0001) α-Al₂O₃]. As shown in Figure 1, we got (100) oriented β-Ga₂O₃ films on MgO and MgAl₂O₄ substrates, (201) oriented β-Ga₂O₃ film on α-Al₂O₃ substrate. The MSM structure β-Ga₂O₃ thin films photodetector were then fabricated to measure the photoelectric properties. Figure 2 shows the on-off switching characteristics of these three photodetectors. It indicates that photoelectric property of β-Ga₂O₃ thin film is strongly correlated with lattice misfit and crystal orientation.

Figure. 1. Out-of-plane XRD patterns for Ga2O3 films grown on different substrates. The reflections labeled by solid symbol come from the MgO substrate (star), MgAl2O4 (triangle), and Al2O3 (square).


Figure. 2. Time-dependent photoresponse (254 nm) of β-Ga2O3 photodetectors on different substrates under an applied bias of 5 V.