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Abnormal phase transition and polarization mismatch phenomena in BaTiO_(3)-based relaxor ferroelectrics

Journal of Advanced Dielectrics 2019年第5期9卷 1-27页

作者： Qingyuan Hu Xiaoyong Wei Electronic Materials Research Laboratory Key Laboratory of the Ministry of Education Xi’an Jiaotong UniversityXi’anShaanxi 710049P.R.China International Center for Dielectric Research School of Electronic Science and Engineering Xi’an Jiaotong University Xi’anShaanxi 710049P.R.China

Relaxor ferroelectrics have been extensively studied due to their outstanding dielectric,piezoelectric,energy storage,and electro-optical *** various theories were proposed to elaborate on the relaxation phenomena,polar nanoregions formed by disruption of the long-range-order structures are considered to play a key role in relaxor ***,relaxor ferro-electrics are formed by aliovalent substitution or isovalent substitution in normal ferroelectrics,or further combinations of solid ***,one category of BaTiO_(3)-based relaxor ferroelectrics with abnormal phase transition and polarization mismatch phenomena is *** parameters of such BaTiO_(3)-based relaxor ferroelectrics,including the Curie temperature,polarization,and lattice parameter,show a typical“U”-shaped variation with *** studied BaTiO_(3)-based relaxor ferroelectrics are mostly solid solutions of A-site coupling and B-site coupling ferroelectrics,exhibiting polarization mismatch in certain compositions[e.g.,0.9BaTiO_(3)-0.1BiScO_(3),0.8BaTiO_(3)-0.2Bi(Mg_(1/2)Ti_(1/2)O_(3),0.8BaTiO_(3)-0.2Bi(Mg_(2/3)Nb_(1/3)O_(3),0.5BaTiO_(3)-0.5Pb(Mg_(1/3)Nb_(2/3)O_(3),0.4BaTiO_(3)-0.6Pb(Zn_(1/3)Nb_(2/3)O_(30,etc.].Of particular interest is that excellent electrical properties can be achieved in the studied relaxor ***,polarization mismatch theory can also provide guidance for the design of new high-performance lead-free relaxor ferroelectrics.

关键词： Relaxor ferroelectrics phase transition polarization mismatch energy storage

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A polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure to improve the hole injection for GaN based micro-LED with secondary etched mesa

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Chinese Physics B 2023年第1期32卷 30-35页

作者：张一丹楚春双杭升张勇辉郑权李青毕文刚张紫辉 State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of TechnologyTianjin 300401China School of Electronics and Information Engineering Hebei University of TechnologyKey Laboratory of Electronic Materials and Devices of TianjinTianjin 300401China School of Electrical Engineering Hebei University of TechnologyTianjin 300401China. State Key Engineering Center of Flat-Panel-Display Glass and Equipment Shijiazhuang 050035China

A low hole injection efficiency for InGaN/GaN micro-light-emitting diodes(μLEDs) has become one of the main bottlenecks affecting the improvement of the external quantum efficiency(EQE) and the optical power. In this work, we propose and fabricate a polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure for 445 nm GaN-based μLEDs with the size of 40 × 40 μm^(2), which serves as the hole injection layer. The polarization-induced electric field in the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure provides holes with more energy and can facilitate the non-equilibrium holes to transport into the active region for radiative recombination. Meanwhile, a secondary etched mesa for μLEDs is also designed, which can effectively keep the holes apart from the defected region of the mesa sidewalls, and the surface nonradiative recombination can be suppressed. Therefore, the proposed μLED with the secondary etched mesa and the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure has the enhanced EQE and the improved optical power density when compared with the μLED without such designs.

关键词： μLED polarization mismatch secondary etched mesa hole injection

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The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiOn/SrTiO3 superlattices

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Chinese Physics B 2007年第6期16卷 1780-1785页

作者：朱振业王彪王海郑跃李青坤 School of Astronautics Harbin Institute of Technology Harbin 150001 China School of Physics and Engineering Sun Yat-sen University Guangzhou 510275 China

We have performed the first-principles calculation to investigate the origins of ferroelectricities and different po- larization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. The density of state （DOS） and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. Ow- ing to the decline of internal electric field in SrTiO3 （ST） layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are en- hanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3.

关键词： ferroelectricity spontaneous polarization polarization mismatch internal electric field

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