Epitaxial Integration Of Ferroelectric-GaN Semiconductor Films And Devices

The integration of ferroelectric film with wide band-gap semiconductor is the key technology for the future applications in power electronics and smart sensor systems.In the research of GaN based high electron mobility transistors(HEMTs),using ferroelectric gate instead of traditional oxide gate,is a effective way to attain enhanced-mode HEMTs.However,there is a big challenge to deposit quality epitaxial ferroelectric films on GaN substrates because of the mismatch between perovskite ferroelectric materials and wurtzite GaN.In this paper we studied the mechanism of epitaxial growth during the PMN-PT films deposition on the GaN substrates,and successfully attained the high quality integration of PMN-PT films on GaN substrates.Then we proposed using ZnO conductive films instead of metal electrodes in order to solve the asymmetry of electrodes in the research of HEMTs.The main conclusions are as follows:(1)PMN-PT films were epitaxially grown on GaN/sapphire substrates via pulsed laser deposition without any intermediated buffer layers.The(111)oriented PMN-PT films were epitaxial grown on GaN(0002),with the in-plane epitaxial relationship of(111)×[-211]PMN-PT//(0002)×[11-20]GaN.(2)A domain matching epitaxy model is proposed to account for the epitaxial growth mechanism of PMN-PT on GaN.(3)The PMN-PT films show typical ferroelectric characteristics,with the remnant polarization and coercive field of 18.1?C/cm~2,which shows great potential for the further development of PMN-PT/GaN based HEMT devices.(4)Zno based conductive films,with the same structure and conduction type and similar lattice parameters,can be used as the top electrode in HEMTs research,which may solve the problem of electrodes asymmetry.The research work in this paper laid the foundation for further development of enhanced-mode of GaN based HEMTs devices,and it is of great significance for the integration of ferroelectric films an GaN-based semiconductors to promote the application of integrated ferroelectric devices.