sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under unia...sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole（HH）-like valence band maximum（VBM） states, while NWs with {11ˉ20} facets have crystal hole（CH）-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum（CBM） of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.展开更多
Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show ...Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V.s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxiai compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.展开更多
Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO i...Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.展开更多
Using the first principle method based on density functional theory, this paper studies the electronic structure and the ferromagnetic stability in N-doped ZnO. The calculated results based on local density approximat...Using the first principle method based on density functional theory, this paper studies the electronic structure and the ferromagnetic stability in N-doped ZnO. The calculated results based on local density approximation （LDA） and LDA＋U method show that ferromagnetism coupling between N atoms is more energetically favourable for eight geometrically distinct configurations. The dominant ferromagnetic interaction is due to the hybridization between O 2p and N 2p. The origin of the ferromagnetic state in N doped ZnO is discussed by analysing coupling between N 2p levels. We also analyse N dopant concentration and lattice strain effect on ferromagnetism.展开更多
The structural and magnetic properties of the Cu-doped ZnO（ZnO：Cu） under c-axis pressure were studied using first-principle calculations. It was found that the ZnO：Cu undergoes a structural transition from Wurtzit...The structural and magnetic properties of the Cu-doped ZnO（ZnO：Cu） under c-axis pressure were studied using first-principle calculations. It was found that the ZnO：Cu undergoes a structural transition from Wurtzite to Graphite-like structure at a c-axis pressure of 7–8 GPa. This is accompanied by an apparent loss of ferromagnetic stability, indicating a magnetic transformation from a ferromagnetic state to a paramagnetic-like state. Further studies revealed that the magnetic instability is closely related to the variation in crystalline field originated from the structural transition, which is in association with the overlapping of spin–charge density between the Cu^2＋ and adjacent O^2-.展开更多
Two-dimensional magnets have received increasing attention since Cr_2Ge_2Te_6 and CrI_3 were experimentally exfoliated and measured in 2017. Although layered ferromagnetic metals were demonstrated at room temperature,...Two-dimensional magnets have received increasing attention since Cr_2Ge_2Te_6 and CrI_3 were experimentally exfoliated and measured in 2017. Although layered ferromagnetic metals were demonstrated at room temperature, a layered ferromagnetic semiconductor with high Curie temperature(Tc) is yet to be unveiled. Here, we theoretically predicted a family of high Tcferromagnetic monolayers, namely MnNX and CrCX(X = Cl, Br and I; C = S, Se and Te). Their Tcvalues were predicted from over 100 K to near 500 K with Monte Carlo simulations using an anisotropic Heisenberg model. Eight members among them show semiconducting bandgaps varying from roughly 0.23 to 1.85 eV. These semiconducting monolayers also show extremely large anisotropy, i.e. ～10~1 for effective masses and ～10~2 for carrier mobilities, along the two in-plane lattice directions of these layers. Additional orbital anisotropy leads to a spin-locked linear dichroism, in different from previously known circular and linear dichroisms in layered materials.Together with the mobility anisotropy, it offers a spin-, dichroism-and mobility-anisotropy locking.These results manifest the potential of this 2D family for both fundamental research and high performance spin-dependent electronic and optoelectronic devices.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11204296 and 61427901)the National Basic Research Program of China(Grant Nos.2014CB643902 and 2013CB933304)
文摘sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole（HH）-like valence band maximum（VBM） states, while NWs with {11ˉ20} facets have crystal hole（CH）-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum（CBM） of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00602)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2011ZX02708-002)
文摘Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V.s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxiai compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0400801)the National Natural Science Foundation of China(Grant Nos.61774128,61674124,11604275,11304257,and 61227009)+1 种基金the Natural Science Foundation of Fujian Province of China(Grant Nos.2017J01012,2014J01026,2016J01037,and 2015J01028)the Fundamental Research Funds for the Central Universities,China(Grant Nos.20720150027,20720160044,20720160122,20720170085,20720170012,and 20720150033)
文摘Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.
基金Project supported by the Science Foundation from the Educational Department of Liaoning Province of China (Grant No. L2010003)
文摘Using the first principle method based on density functional theory, this paper studies the electronic structure and the ferromagnetic stability in N-doped ZnO. The calculated results based on local density approximation （LDA） and LDA＋U method show that ferromagnetism coupling between N atoms is more energetically favourable for eight geometrically distinct configurations. The dominant ferromagnetic interaction is due to the hybridization between O 2p and N 2p. The origin of the ferromagnetic state in N doped ZnO is discussed by analysing coupling between N 2p levels. We also analyse N dopant concentration and lattice strain effect on ferromagnetism.
基金supported by the National Natural Science Foundation of China(Grant Nos.51031004 and 51272078)the Natural Science Foundation of Guangdong,China(Grant No.S2012010008124)+3 种基金the National Basic Research Program of China(Grant No.2015CB921202)the Project for Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme(2014)International Science & Technology Cooperation Platform Program of Guangzhou,China(Grant No.2014J4500016)the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(Grant No.IRT1243)
文摘The structural and magnetic properties of the Cu-doped ZnO（ZnO：Cu） under c-axis pressure were studied using first-principle calculations. It was found that the ZnO：Cu undergoes a structural transition from Wurtzite to Graphite-like structure at a c-axis pressure of 7–8 GPa. This is accompanied by an apparent loss of ferromagnetic stability, indicating a magnetic transformation from a ferromagnetic state to a paramagnetic-like state. Further studies revealed that the magnetic instability is closely related to the variation in crystalline field originated from the structural transition, which is in association with the overlapping of spin–charge density between the Cu^2＋ and adjacent O^2-.
基金supported by the National Natural Science Foundation of China(11274380,91433103,11622437 and 61674171)the Fundamental Research Funds for the Central Universities of China+2 种基金the Research Funds of Renmin University of China(16XNLQ01)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB30000000)supported by the Outstanding Innovative Talents Cultivation Funded Programs 2017 of Renmin University of China
文摘Two-dimensional magnets have received increasing attention since Cr_2Ge_2Te_6 and CrI_3 were experimentally exfoliated and measured in 2017. Although layered ferromagnetic metals were demonstrated at room temperature, a layered ferromagnetic semiconductor with high Curie temperature(Tc) is yet to be unveiled. Here, we theoretically predicted a family of high Tcferromagnetic monolayers, namely MnNX and CrCX(X = Cl, Br and I; C = S, Se and Te). Their Tcvalues were predicted from over 100 K to near 500 K with Monte Carlo simulations using an anisotropic Heisenberg model. Eight members among them show semiconducting bandgaps varying from roughly 0.23 to 1.85 eV. These semiconducting monolayers also show extremely large anisotropy, i.e. ～10~1 for effective masses and ～10~2 for carrier mobilities, along the two in-plane lattice directions of these layers. Additional orbital anisotropy leads to a spin-locked linear dichroism, in different from previously known circular and linear dichroisms in layered materials.Together with the mobility anisotropy, it offers a spin-, dichroism-and mobility-anisotropy locking.These results manifest the potential of this 2D family for both fundamental research and high performance spin-dependent electronic and optoelectronic devices.
