In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field p...In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.展开更多
The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n...The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface,the interface Ti3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of Ba TiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2p y state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface Mg O layer leads to a magnetic moment of about 0.25μB per O atom at the interface.These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces.展开更多
We report an abnormal phenomenon that the source-drain current(I_(D))of AlGaN/GaN heterostructure devices decreases under visible light irradiation.When the incident light wavelength is 390 nm,the photon energy is les...We report an abnormal phenomenon that the source-drain current(I_(D))of AlGaN/GaN heterostructure devices decreases under visible light irradiation.When the incident light wavelength is 390 nm,the photon energy is less than the band gaps of GaN and AlGaN whereas it can causes an increase of ID.Based on the UV light irradiation,a decrease of I_(D) can still be observed when turning on the visible light.We speculate that this abnormal phenomenon is related to the surface barrier height,the unionized donor-like surface states below the surface Fermi level and the ionized donor-like surface states above the surface Fermi level.For visible light,its photon energy is less than the surface barrier height of the AlGaN layer.The electrons bound in the donor-like surface states below the Fermi level are excited and trapped by the ionized donor-like surface states between the Fermi level and the conduction band of AlGaN.The electrons trapped in ionized donor-like surface states show a long relaxation time,and the newly ionized donor-like surface states below the surface Fermi level are filled with electrons from the two-dimensional electron gas(2DEG)channel at AlGaN/GaN interface,which causes the decrease of ID.For the UV light,when its photon energy is larger than the surface barrier height of the AlGaN layer,electrons in the donor-like surface states below the Fermi level are excited to the conduction band and then drift into the 2DEG channel quickly,which cause the increase of ID.展开更多
Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electro...Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electron gas （2DEG） at oxide interfaces. Due to the presence of oxygen vacancies at the SrTiO3 surface, metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3 has Al, Ti, Zr, or Hf elements at the B sites. Furthermore, relying on interface-stabilized oxygen vacancies, we have created a new type of 2DEG at the heterointerface between SrTiO3 and a spinel γ-Al2O3 epitaxial film with compatible oxygen ion sublattices. This 2DEG exhibits an electron mobility exceeding 100000 cm2·V-1·s-1, more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces. Our findings pave the way for the design of high-mobility all-oxide electronic devices and open a route toward the studies of mesoscopic physics with complex oxides.展开更多
Density functional theory within the local density approximation is used to investigate the effect of the oxygen va- cancy on the LaGaO3/SrTiO3 （001） heterojunction. It is found that the energy favorable configurati...Density functional theory within the local density approximation is used to investigate the effect of the oxygen va- cancy on the LaGaO3/SrTiO3 （001） heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3rd layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO3 side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas （2DEG）, that is, the 2DEG still originates from the dxy electrons, which are split from the t2g states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3dx2-y2 orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.展开更多
We studied and compared the transport properties of charge carriers in bilayer graphene, monolayer graphene, and the conventional semiconductors （the two-dimensional electron gas （2DEG））. It is elucidated that the...We studied and compared the transport properties of charge carriers in bilayer graphene, monolayer graphene, and the conventional semiconductors （the two-dimensional electron gas （2DEG））. It is elucidated that the normal incidence transmission in the bilayer graphene is identical to that in the 2DEG but totally different from that in the monolayer graphene. However, resonant peaks appear in the non-normal incidence transmission profile for a high barrier in the bilayer graphene, which do not occur in the 2DEG. Furthermore, there are tunneling and forbidden regions in the transmission spectrum for each material, and the division of the two regions has been given in the work. The tunneling region covers a wide range of the incident energy for the two graphene systems, but only exists under specific conditions for the 2DEG. The counterparts of the transmission in the conductance profile are also given for the three materials, which may be used as high-performance devices based on the bilayer graphene.展开更多
Electrical properties of an AIlnN/GaN high-electron mobility transistor （HEMT） on a sapphire substrate are investigated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation cur...Electrical properties of an AIlnN/GaN high-electron mobility transistor （HEMT） on a sapphire substrate are investigated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AIInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61106076)
文摘In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.
基金supported by the National Basic Research Program of China(Grant No.2013CB632506)the National Natural Science Foundation of China(Grant Nos.11374186,51231007,51202132,and 51102153)the Independent Innovation Foundation of Shandong University,China(Grant No.2012TS027)
文摘The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface,the interface Ti3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of Ba TiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2p y state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface Mg O layer leads to a magnetic moment of about 0.25μB per O atom at the interface.These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces.
基金Project supported by Key-Area Research and Development Program of Guangdong Province,China(Grant Nos.2019B010132001 and 2019B010132003)the Joint Funding of the National Natural Science Foundation of China(NSFC)&the Macao Science and Technology Development Fund(FDCT)of China(Grant No.62061160368)+1 种基金the National Key Research and Development Program of China(Grant Nos.2016YFB0400105 and 2017YFB0403001)the Zhuhai Key Technology Laboratory of Wide Bandgap Semiconductor Power Electronics,Sun Yat-sen University,China(Grant No.20167612042080001).
文摘We report an abnormal phenomenon that the source-drain current(I_(D))of AlGaN/GaN heterostructure devices decreases under visible light irradiation.When the incident light wavelength is 390 nm,the photon energy is less than the band gaps of GaN and AlGaN whereas it can causes an increase of ID.Based on the UV light irradiation,a decrease of I_(D) can still be observed when turning on the visible light.We speculate that this abnormal phenomenon is related to the surface barrier height,the unionized donor-like surface states below the surface Fermi level and the ionized donor-like surface states above the surface Fermi level.For visible light,its photon energy is less than the surface barrier height of the AlGaN layer.The electrons bound in the donor-like surface states below the Fermi level are excited and trapped by the ionized donor-like surface states between the Fermi level and the conduction band of AlGaN.The electrons trapped in ionized donor-like surface states show a long relaxation time,and the newly ionized donor-like surface states below the surface Fermi level are filled with electrons from the two-dimensional electron gas(2DEG)channel at AlGaN/GaN interface,which causes the decrease of ID.For the UV light,when its photon energy is larger than the surface barrier height of the AlGaN layer,electrons in the donor-like surface states below the Fermi level are excited to the conduction band and then drift into the 2DEG channel quickly,which cause the increase of ID.
文摘Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electron gas （2DEG） at oxide interfaces. Due to the presence of oxygen vacancies at the SrTiO3 surface, metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3 has Al, Ti, Zr, or Hf elements at the B sites. Furthermore, relying on interface-stabilized oxygen vacancies, we have created a new type of 2DEG at the heterointerface between SrTiO3 and a spinel γ-Al2O3 epitaxial film with compatible oxygen ion sublattices. This 2DEG exhibits an electron mobility exceeding 100000 cm2·V-1·s-1, more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces. Our findings pave the way for the design of high-mobility all-oxide electronic devices and open a route toward the studies of mesoscopic physics with complex oxides.
基金Project supported by the National Basic Research Program of China(Grant No.2013CB632506)the National Natural Science Foundation of China(Grant Nos.11374186,51231007,and 51202132)
文摘Density functional theory within the local density approximation is used to investigate the effect of the oxygen va- cancy on the LaGaO3/SrTiO3 （001） heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3rd layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO3 side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas （2DEG）, that is, the 2DEG still originates from the dxy electrons, which are split from the t2g states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3dx2-y2 orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.
基金the National Natural Science Foundation of China(Grant No.11104156)the Postdoctoral Science Foundation of China(Grant No.2012M510405)+1 种基金the Independent Research and Development Fund of Tsinghua University,China(Grant No.20121087948)the Beijing Key Lab of Fine Ceramics Opening Fund,China(Grant No.2012200110)
文摘We studied and compared the transport properties of charge carriers in bilayer graphene, monolayer graphene, and the conventional semiconductors （the two-dimensional electron gas （2DEG））. It is elucidated that the normal incidence transmission in the bilayer graphene is identical to that in the 2DEG but totally different from that in the monolayer graphene. However, resonant peaks appear in the non-normal incidence transmission profile for a high barrier in the bilayer graphene, which do not occur in the 2DEG. Furthermore, there are tunneling and forbidden regions in the transmission spectrum for each material, and the division of the two regions has been given in the work. The tunneling region covers a wide range of the incident energy for the two graphene systems, but only exists under specific conditions for the 2DEG. The counterparts of the transmission in the conductance profile are also given for the three materials, which may be used as high-performance devices based on the bilayer graphene.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61204018)
文摘Electrical properties of an AIlnN/GaN high-electron mobility transistor （HEMT） on a sapphire substrate are investigated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AIInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.
