17 results on '"Chao Zhao"'
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2. Band alignment between (100)Si and complex rare earth∕transition metal oxides
- Author
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Jürgen Schubert, Y. Jia, Darrell G. Schlom, Matty Caymax, Andre Stesmans, Chao Zhao, Tassilo Heeg, Valeri Afanas'ev, and Gerald Lucovsky
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Materials science ,Physics and Astronomy (miscellaneous) ,Band gap ,Photoconductivity ,Relaxation (NMR) ,Inorganic chemistry ,Molecular physics ,Semimetal ,Amorphous solid ,Metal ,Transition metal ,visual_art ,visual_art.visual_art_medium ,ddc:530 ,Direct and indirect band gaps - Abstract
The electron energy band alignment between (100)Si and several complex transition/rare earth (RE) metal oxides (LaScO3, GdScO3, DyScO3, and LaAlO3, all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides (5.6-5.7 eV) yielding the conduction and valence band offsets at the Si/oxide interface of 2.0+/-0.1 and 2.5+/-0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states. (C) 2004 American Institute of Physics.
- Published
- 2004
3. Deposition of HfO2 on germanium and the impact of surface pretreatments
- Author
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Stefan Kubicek, M.M. Heyns, J. Van Steenbergen, Thierry Conard, M. Meuris, Bert Brijs, S. De Gendt, Bart Onsia, Matty Caymax, Chao Zhao, S. Van Elshocht, O. Richard, B. De Jaeger, Ivo Teerlinck, and T. Chiarella
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Surface diffusion ,Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,Inorganic chemistry ,chemistry.chemical_element ,Germanium ,Chemical vapor deposition ,chemistry ,Surface roughness ,Metalorganic vapour phase epitaxy ,Composite material ,Layer (electronics) ,Deposition (law) - Abstract
The deposition behavior of HfO2 by metalorganic chemical vapor deposition on germanium has been investigated. HfO2 films can be deposited on Ge with equally good quality as compared to high-k growth on silicon. Surface preparation is very important: compared to an HF-last, NH3 pretreatments result in smoother films with strongly reduced diffusion of germanium in the HfO2 film, resulting in a much better electrical performance. We clearly show that much thinner interfacial layers can be obtained, approximately half the thickness of what is typically found for depositions on silicon, suggesting the possibility of more aggressive equivalent oxide thickness∕leakage scaling.
- Published
- 2004
4. Impact of annealing-induced compaction on electronic properties of atomic-layer-deposited Al2O3
- Author
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B. J. Mrstik, Chao Zhao, Valeri Afanas'ev, and Andre Stesmans
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Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Band gap ,Annealing (metallurgy) ,Fermi level ,Oxide ,Compaction ,Dielectric ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,symbols ,Grain boundary ,Leakage (electronics) - Abstract
Atomic-layer-deposited layers of Al2O3 on (100)Si are shown to transform into γ-Al2O3 when treated at temperatures above 800 °C. The compaction process leads to widening of the alumina band gap and causes an ≈0.5 eV upward shift of the oxide conduction band with respect to the Fermi level of Au and Al. In the case of incomplete transformation of the Al2O3 film, large leakage currents across the oxide are observed, which are explained by the formation of conducting grain boundaries similar to those formed on γ-alumina surfaces.
- Published
- 2002
5. Miscibility of amorphous ZrO2–Al2O3 binary alloy
- Author
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Chao Zhao, Suvi Haukka, M.M. Heyns, O. Richard, Hugo Bender, S. De Gendt, E. Young, Matty Caymax, Gert Roebben, and O. Van der Biest
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Materials science ,Physics and Astronomy (miscellaneous) ,Annealing (metallurgy) ,Chemical vapor deposition ,Miscibility ,law.invention ,Amorphous solid ,Crystallography ,Transmission electron microscopy ,law ,gate ,X-ray crystallography ,Wafer ,Composite material ,Crystallization - Abstract
Miscibility is a key factor for maintaining the homogeneity of the amorphous structure in a ZrO2-Al2O3 binary alloy high-k dielectric layer. In the present work, a ZrO2/Al2O3 laminate thin layer has been prepared by atomic layer chemical vapor deposition on a Si (100) wafer. This layer, with artificially induced inhomogeneity (lamination), enables one to study the change in homogeneity of the amorphous phase in the ZrO2/Al2O3 system during annealing. High temperature grazing incidence x-ray diffraction (HT-XRD) was used to investigate the change in intensity of the constructive interference peak of the x-ray beams which are reflected from the interfaces of ZrO2/Al2O3 laminae. The HT-XRD spectra show that the intensity of the peak decreases with an increase in the anneal temperature, and at 800 degreesC, the peak disappears. The same samples were annealed by a rapid thermal process (RTP) at temperatures between 700 and 1000 degreesC for 60 s. Room temperature XRD of the RTP annealed samples shows a similar decrease in peak intensity. Transmission electronic microscope images confirm that the laminate structure is destroyed by RTP anneals and, just below the crystallization onset temperature, a homogeneous amorphous ZrAlxOy phase forms. The results demonstrate that the two artificially separated phases, ZrO2 and Al2O3 laminae, tend to mix into a homogeneous amorphous phase before crystallization. This observation indicates that the thermal stability of ZrO2-Al2O3 amorphous phase is suitable for high-k applications. (C) 2002 American Institute of Physics. ispartof: Applied Physics Letters vol:80 issue:13 pages:2374-2376 status: published
- Published
- 2002
6. Physical understanding of different drain-induced-barrier-lowering variations in high-k/metal gate n-channel metal-oxide-semiconductor-field-effect-transistors induced by charge trapping under normal and reverse channel hot carrier stresses
- Author
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Hao Xu, Zhaoyun Tang, Hong Yang, Dapeng Chen, Jing Xu, Chao Zhao, Tianchun Ye, Yefeng Xu, Wenwu Wang, Weichun Luo, Jiang Yan, Bo Tang, Shangqing Ren, and Lichuan Zhao
- Subjects
Stress (mechanics) ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,MOSFET ,Pinch ,Optoelectronics ,Field-effect transistor ,Drain-induced barrier lowering ,Trapping ,business ,Metal gate ,High-κ dielectric - Abstract
In this paper, the drain induced barrier lowering (DIBL) variations in High-k/Metal gate n-channel metal–oxide–semiconductor field effect transistor under the normal and reverse channel hot carrier (CHC) stress are studied. It is found that DIBL decreases under normal CHC stress mode while increases under reverse CHC mode. The different DIBL variation under normal and reverse CHC stresses is proposed to be attributed to stress-induced charge trapping by cold carriers from the channel rather than hot carriers from the pinch off region, which can be explained by energy band bending theory.
- Published
- 2013
7. Mechanism of Ti/Al/Ti/W Au-free ohmic contacts to AlGaN/GaN heterostructures via pre-ohmic recess etching and low temperature annealing.
- Author
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Jinhan Zhang, Sen Huang, Qilong Bao, Xinhua Wang, Ke Wei, Yingkui Zheng, Yankui Li, Chao Zhao, Xinyu Liu, Qi Zhou, Wanjun Chen, and Bo Zhang
- Subjects
OHMIC contacts ,HETEROSTRUCTURES ,ALUMINUM gallium nitride ,LOW temperatures ,ANNEALING of crystals - Abstract
The physical mechanism of low-thermal-budget Au-free ohmic contacts to AlGaN/GaN heterostructures is systematically investigated with current-voltage, high-resolution transmission electron microscopy, and temperature-dependent contact resistivity characterizations. With a low annealing temperature of 600 °C, pre-ohmic recess etching of the AlGaN barrier down to several nanometers is demonstrated to be an effective method to reduce the contact resistance between Ti/Al/Ti/W ohmic metals and AlGaN/GaN heterostructures. However, further over recess of the AlGaN barrier leads to only sidewall contact to 2D electron gas channel and thus degraded contact performance. It is verified by temperature-dependent contact resistivity measurements that field emission(tunneling) dominates the current transport mechanism in Au-free ohmic contacts with AlGaN barrier partially and over recessed, while both field emission and thermionic emission contribute to traditional Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures that annealed at high temperature (850 °C). [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
8. Ultra-shallow junctions formed using microwave annealing
- Author
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Dongping Wu, Chao Zhao, Chaochao Fu, Peng Xu, Zhibin Zhang, Cheng Hu, Shi-Li Zhang, David Wei Zhang, and Jun Luo
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Materials science ,Physics and Astronomy (miscellaneous) ,Dopant ,Silicon ,business.industry ,Annealing (metallurgy) ,Doping ,chemistry.chemical_element ,Nanotechnology ,Germanium ,Amorphous solid ,Ion implantation ,chemistry ,Thermal ,Optoelectronics ,business - Abstract
Microwave annealing is shown to be viable for achieving low thermal budget formation of ultra-shallow junctions. Regrowth of a 10 nm thick amorphous Si layer that is generated during a Ge amorphization process prior to BF2 or As dopant implantation proceeds at rates up to 0.53 nm/min for BF2 and up to 0.33 nm/min for As at 370 °C. The fraction of electrical activation for implanted dopants is as high as 13% for BF2 and 32% for As with negligible diffusion at 540 °C.
- Published
- 2013
9. A possible origin of core-level shift in SiO2/Si stacks
- Author
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Xiaolei Wang, Jing Zhang, Xueli Ma, Dapeng Chen, Chao Zhao, Jinjuan Xiang, Hong Yang, Kai Han, Wenwu Wang, and Tianchun Ye
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Auger electron spectroscopy ,Physics and Astronomy (miscellaneous) ,Silicon ,Chemistry ,Band gap ,Fermi level ,chemistry.chemical_element ,Electron ,Molecular physics ,symbols.namesake ,X-ray photoelectron spectroscopy ,symbols ,Atomic physics ,Voltage drop ,Energy (signal processing) - Abstract
Band alignments of SiO2/Si stacks with different SiO2 thicknesses are re-examined by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy. The energy difference between core-levels of SiO2 and Si is found to decrease with thicker SiO2. A possible explanation based on surface gap states (SGS) and charge neutrality level (CNL) is proposed to elucidate band alignment of SiO2/Si. Due to lower CNL of SiO2 SGS than Fermi level of Si, electrons transfer from Si to SiO2 SGS. With thicker SiO2 fewer electrons transfer from Si to SiO2, resulting in larger potential drop across SiO2 and XPS results.
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- 2013
10. Reexamination of band offset transitivity employing oxide heterojunctions
- Author
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Xueli Ma, Hong Yang, Dapeng Chen, Jing Zhang, Chao Zhao, Jinjuan Xiang, Xiaolei Wang, Kai Han, Tianchun Ye, and Wenwu Wang
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chemistry.chemical_compound ,Nanostructure ,Physics and Astronomy (miscellaneous) ,X-ray photoelectron spectroscopy ,chemistry ,Condensed matter physics ,Band gap ,Valence band ,Oxide ,Analytical chemistry ,Heterojunction ,Hafnium compounds ,Band offset - Abstract
Band offset transitivity is reexamined extendedly by employing oxide heterojuctions. The valence band offsets (ΔEV) at HfO2/SiO2, Al2O3/SiO2, and HfO2/Al2O3 heterojunctions are experimentally determined to be 0.81, 0.25, and 0.25 eV, respectively, by X-ray photoelectron spectroscopy. Thus, the ΔEV at HfO2/Al2O3 heterojunction is not equal to the ΔEV at HfO2/SiO2 minus the ΔEV at Al2O3/SiO2 heterostructures (0.25 ≠ 0.81 − 0.25 = 0.56), i.e., the transitivity rule fails for oxide heterojunctions. Different distributions of interfacial induced gap states at the three heterostructures contribute to this failure of transitivity rule.
- Published
- 2013
11. Surface acoustic wave nebulization on nanocrystalline ZnO film
- Author
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Frank Placido, Yong Qing Fu, Anthony J. Walton, Yifan Li, and Chao Zhao
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Fabrication ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Surface acoustic wave ,Wide-bandgap semiconductor ,Integrated circuit ,Semiconductor device ,law.invention ,Wavelength ,law ,Optoelectronics ,Microelectronics ,Radio frequency ,business - Abstract
Surface acoustic wave(SAW) nebulization/atomization has been realised on thin ZnOfilm based SAWdevices. The surface acoustic wave nebulization (SAWN) process has been observed to produce significant mist generation and ejected satellitedroplets. By modifying the geometry of the interdigitated transducers to reduce the wavelengths from 400 μm to 120 μm, higher frequency SAWN has been achieved by increasing radio frequency driving frequencies from 11.8 MHz to 37.2 MHz, respectively. Compared with the commonly used LiNbO3 SAWN devices,ZnOfilmdevices exhibit better thermal dissipation, and to date, they have shown no susceptibility to substrate failure during fabrication or operation. They also have the added advantage of the technology being suitable for direct integration with microsystems and integrated circuit microelectronics.
- Published
- 2012
12. Band alignment of HfO2 on SiO2/Si structure
- Author
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Xueli Ma, Jing Zhang, Hong Yang, Dapeng Chen, Chao Zhao, Jinjuan Xiang, Xiaolei Wang, Tianchun Ye, Kai Han, and Wenwu Wang
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Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,Band gap ,Oxide ,chemistry.chemical_element ,Heterojunction ,Molecular physics ,Crystallography ,chemistry.chemical_compound ,Semiconductor ,Band bending ,X-ray photoelectron spectroscopy ,chemistry ,business ,Surface states - Abstract
Band alignment of HfO2 with various thicknesses on SiO2/Si structure is investigated by x-ray photoelectron spectroscopy (XPS). Band bending of HfO2/SiO2/Si system is found to vary with HfO2 thickness. Band alignment of entire HfO2/SiO2/Si is demonstrated using concepts of interfacial or surface gap states and charge neutrality level (CNL). The XPS results are interpreted and attributed to lower CNL of HfO2 than SiO2/Si which induces electron transfer from SiO2/Si to HfO2, resulting in band bending upward for SiO2/Si. These further confirm feasibility of gap state based theory in investigating band alignments of oxide/semiconductor and oxide/oxide interfaces.
- Published
- 2012
13. UV irradiation induced switching of surface charge polarity on pyrene modified Si nanowires
- Author
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Wen-Chao Zhao, Xue-Mei Ou, Chun-Sing Lee, Xiaohong Zhang, and Hui Wang
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Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,Polarity (physics) ,Nanowire ,chemistry.chemical_element ,Photochemistry ,Nanomaterials ,Chemical species ,chemistry.chemical_compound ,chemistry ,Optoelectronics ,Pyrene ,Irradiation ,Surface charge ,business - Abstract
It has been widely recognized that surface charge in nanomaterials can significantly affect their electrical properties. In this letter, we demonstrate that polarity of surface charge on pyrene modified silicon nanowires (SiNWs) can be switched by illumination of UV light. Unlike the reported conversion method via changing the surrounding pH value, switching process reported here takes place in real-time and does not require introduction of any other chemical species. Mechanisms of the surface charge polarity switching and potential applications of such systems were discussed.
- Published
- 2011
14. Polarization offsets of compositionally graded Nd-substituted Bi4Ti3O12 ferroelectric thin films
- Author
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Di Wu, Zhen Fu, Chao Zhao, Aidong Li, and Hao Wu
- Subjects
Amplitude ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,media_common.quotation_subject ,Ferroelectric thin films ,Dielectric hysteresis ,Polarization (waves) ,Asymmetry ,Ferroelectricity ,media_common ,Voltage ,Leakage (electronics) - Abstract
The vertical offsets of hysteresis loops of compositionally graded Nd-substituted Bi4Ti3O12 (BNdT) ferroelectric films were studied as functions of the Nd gradient, the temperature, and the amplitude of driving voltage. We show that graded BNdT films may exhibit no offsets at room temperature and both graded and nongraded BNdT films exhibit pronounced offsets at elevated temperatures. The offset does not have a direct relation with the composition gradient but increases as the maximum voltage is increased. It is verified that the offset increases with the increase in asymmetry of leakage currents at positive and negative biases.
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- 2008
15. Evolution of InAs nanostructures grown by droplet epitaxy
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Bingshe Xu, Ping Jin, Z.G. Wang, Yu Chen, and Chao Zhao
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Materials science ,Nanostructure ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Condensed Matter::Other ,Nucleation ,chemistry.chemical_element ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Critical value ,Epitaxy ,Condensed Matter::Materials Science ,chemistry ,Quantum dot ,Indium ,Deposition (law) ,Molecular beam epitaxy - Abstract
The authors report the growth evolution of InAs dot and ring nanostructures with the indium deposition amount on GaAs (001) by droplet molecular beam epitaxy. There is a critical flux for the indium to form InAs dots even when there is no droplet. When the flux exceeds a critical value, In droplets form, which act as nucleation centers for the formation of InAs rings. (C) 2007 American Institute of Physics.
- Published
- 2007
16. Band alignment at the interface of (100)Si with Hf[sub x]Ta[sub 1−x]O[sub y] high-κ dielectric layers
- Author
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Chao Zhao, Z. M. Rittersma, Andre Stesmans, Matty Caymax, Valeri Afanas'ev, and J. W. Maes
- Subjects
Valence (chemistry) ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Band gap ,Photoconductivity ,Oxide ,Heterojunction ,Dielectric ,Semimetal ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Atomic physics - Abstract
The alignment of the conduction and valence bands in metal∕mixed Hf–Ta oxide∕silicon structures was determined as a function of oxide composition using intrinsic photoconductivity and internal photoemission measurements. With increasing Ta content in the Hf–Ta oxide from 0% to 100%, the band gap gradually decreases from 5.6 to 4.2–4.4eV. This is predominantly associated with the downshift of the lowest conduction band derived from the 5d* unoccupied orbitals of the metal cations. This indicates a significant mixing of the states belonging to the Ta and Hf subnetworks, and suggests the possibility of oxide band gap control in the mixed oxides of metals from the same period of elements.
- Published
- 2005
17. Polarization offsets of compositionally graded Nd-substituted Bi4Ti3O12 ferroelectric thin films.
- Author
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Di Wu, Hao Wu, Zhen Fu, Chao Zhao, and Aidong Li
- Subjects
FERROELECTRIC crystals ,FERROELECTRIC thin films ,HYSTERESIS loop ,AMPLITUDE variation with offset analysis ,STRAY currents ,TEMPERATURE ,ELECTRIC potential ,POLARIZATION (Electricity) - Abstract
The vertical offsets of hysteresis loops of compositionally graded Nd-substituted Bi
4 Ti3 O12 (BNdT) ferroelectric films were studied as functions of the Nd gradient, the temperature, and the amplitude of driving voltage. We show that graded BNdT films may exhibit no offsets at room temperature and both graded and nongraded BNdT films exhibit pronounced offsets at elevated temperatures. The offset does not have a direct relation with the composition gradient but increases as the maximum voltage is increased. It is verified that the offset increases with the increase in asymmetry of leakage currents at positive and negative biases. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
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