In thermoelectrics,the manipulation of crystal symmetry is instrumental in optimizing the electrical and thermal transport parameters.Within this context,the present study explored the largely overlooked high-symmetry...In thermoelectrics,the manipulation of crystal symmetry is instrumental in optimizing the electrical and thermal transport parameters.Within this context,the present study explored the largely overlooked high-symmetry cubic GeSe,which presented larger band degeneracy than its widely studied medium-symmetry rhombohedral counterpart.We have successfully stabilized cubic Ge Se a ambient conditions through co-alloying with AgSnTe_(2)and Bi.The incorporation of AgSnTe_(2)initiates the transition of GeSe from a low-symmetry orthorhombic to a mediumsymmetry rhombohedral phase,culminating in a highsymmetry cubic structure,underpinned by variation in chemical bonding mechanisms.Notwithstanding this,the persistence of Ag_(2)Te precipitates impedes the total elimination of the residual orthorhombic phase due to the disparate chemical bonding mechanism between Ag_(2)Te and GeSe.Introducing Bi into the rhombohedral-dominated(GeSe)_(0.7)(AgSnTe_(2))_(0.3)matrix leads to the dissolution of Ag_(2)Te precipitates,elimination of the residual orthorhombic phase,and the subsequent stabilization of the exclusive cubic phase.Compared to its orthorhombic counterpart,the cubic GeSe exhibits diminished bandgap and Ge vacancy formation energy,amplified band degeneracy,reduced sound velocity,intensified lattice anharmonicity and multiple phonon scattering centres engendering elevated carrier concentration and density-ofstates effective mass,alongside restrained lattice therma conductivity.Consequently,a peak zT of 0.46 at 573 K is attained for cubic(Ge_(0.7)Bi_(0.3)Se)_(0.7)(AgSnTe_(2))_(0.3),signifying a ninefold increase relative to the initial orthorhombic Ge Se.These results illuminate the critical role of crystal symmetry manipulation in advancing the thermoelectric performance.展开更多
The successful deployment of thermoelectric materials necessitates the concurrent development of highperformance p-type and n-type pairs situated within an identical matrix.Nevertheless,limiting by the low dopant solu...The successful deployment of thermoelectric materials necessitates the concurrent development of highperformance p-type and n-type pairs situated within an identical matrix.Nevertheless,limiting by the low dopant solubility,the conventional doping often cannot transfer the Fermi level to the opposite carrier type.Here,the solubility limit of donor dopants was enhanced to achieve n-type GeSe by inducing additional cationic vacancies through raising crystal symmetry.Converting the intrinsic p-type nature of GeSe to n-type poses significant challenges,primarily due to the exceedingly low dopant solubility within its native orthorhombic structure.To overcome this,the In_(2)Te_(3)alloying was initially employed to transition GeSe from orthorhombic to rhombohedral structure,simultaneously generating a large number of Ge vacancies.Following this,the introduction of Pb acts to mitigate the excessive Ge vacancies,steering the material toward a weak p-type character.Crucially,the elevated Ge vacancy concentration serves to extend the solubility limit of Bi donor dopant,which not only promotes the formation of cubic phase,but also enables the p-n type transition.As a result,a peak zT of 0.18 at 773 K was attained for the n-type cubic Ge_(0.55)Bi_(0.2)Pb_(0.2)5Se(In_(2)Te_(3))_(0.1),marking an 18-fold enhancement in comparison with its n-type orthorhombic counterpart.This work attests to the efficacy of introducing vacancies through enhancing crystal symmetry as an effective means to expand dopant solubility,thereby offering valuable insights into the achievement of compatible p-and n-type chalcogenides within the same matrix.展开更多
Ge-based selenides have attracted extensive attention as promising candidates for future optoelectronic applications.Despite great progress has been achieved,the controlled synthesis of GeSe2and GeSe nanostructures an...Ge-based selenides have attracted extensive attention as promising candidates for future optoelectronic applications.Despite great progress has been achieved,the controlled synthesis of GeSe2and GeSe nanostructures and understanding the relative growth mechanisms of them are still lacking.Herein,monodispersed GeSe_(2) nanoflowers with a diameter of~4μm and highly uniform GeSe nanoparticles with a lateral size of~100 nm are presented by using a colloidal synthetic method.It is found that borane tert-butylamine complex(TBAB)plays an important role in determining the Ge-Se crystal phases due to its moderately reducibility.Furthermore,the coexistence of GeSe_(2) and GeSe phases can also be acquired by precisely controlling the amount of TBAB.In brief,this work provides both new insights of the phase control of Gebased selenides by liquid-phase method and a practical means of producing well-controlled germanium selenide nanostructures.展开更多
GeSe nanosheets were prepared by ultrasonic-assisted liquid<span><span><span style="font-family:;" "=""> </span></span></span><span><span><sp...GeSe nanosheets were prepared by ultrasonic-assisted liquid<span><span><span style="font-family:;" "=""> </span></span></span><span><span><span><span style="font-family:Verdana;">phase exfoliation (LPE), and the nonlinear saturated absorption performance was experimentally studied. The modulation depth and saturation intensity of the prepared GeSe saturable absorber (SA) were 15% and 1.44 MW/cm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, respectively. Us</span><span style="font-family:Verdana;">ing the saturated absorption characteristics of GeSe SA, a passively Q-switched </span><span style="font-family:Verdana;">erbium-doped fiber laser was systematically demonstrated. As the pump</span><span style="font-family:Verdana;"> power increases, the pulse repetition frequency increases from 22.8 kHz to 77.59 </span><span style="font-family:Verdana;">kHz. The shortest pulse duration is 1.51 μs, and the corresponding pulse</span><span style="font-family:Verdana;"> energy is 46.14 nJ. Experimental results show that GeSe nanosheets can be used as high-efficiency SA in fiber lasers. Our results will provide a useful reference for demonstrating pulsed fiber lasers based on GeSe equipment.</span></span></span></span>展开更多
Selector devices are indispensable components of large-scale memristor array systems.The thereinto,ovonic threshold switching(OTS)selector is one of the most suitable candidates for selector devices,owing to its high ...Selector devices are indispensable components of large-scale memristor array systems.The thereinto,ovonic threshold switching(OTS)selector is one of the most suitable candidates for selector devices,owing to its high selectivity and scalability.However,OTS selectors suffer from poor endurance and stability which are persistent tricky problems for applica-tion.Here,we report on a multilayer OTS selector based on simple GeSe and doped-GeSe.The experimental results show im-proving selector performed extraordinary endurance up to 1010 and the fluctuation of threshold voltage is 2.5%.The reason for the improvement may lie in more interface states which strengthen the interaction among individual layers.These develop-ments pave the way towards tuning a new class of OTS materials engineering,ensuring improvement of electrical perform-ance.展开更多
GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity.However,the efficiency of GeSe thin-film solar cells(TF...GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity.However,the efficiency of GeSe thin-film solar cells(TFSCs)is still low compared to the Shockley–Queisser limit.Point defects are believed to play important roles in the electrical and optical properties of GeSe thin films.Here,we perform first-principles calculations to study the defect characteristics of GeSe.Our results demonstrate that no matter under the Ge-rich or Se-rich condition,the Fermi level is always located near the valence band edge,leading to the p-type conductivity of undoped samples.Under Se-rich condition,the Ge vacancy(V_(Ge))has the lowest formation energy,with a(0/2–)charge-state transition level at 0.22 eV above the valence band edge.The high density(above 10^(17)cm^(-3))and shallow level of VGeimply that it is the p-type origin of GeSe.Under Se-rich growth condition,Seihas a low formation energy in the neutral state,but it does not introduce any defect level in the band gap,suggesting that it neither contributes to electrical conductivity nor induces non-radiative recombination.In addition,Gei introduces a deep charge-state transition level,making it a possible recombination center.Therefore,we propose that the Se-rich condition should be adopted to fabricate high-efficiency GeSe solar cells.展开更多
基金financially supported by the National Key R&D Program of China(No.2021YFB1507403)the National Natural Science Foundation of China(No.52071218)+1 种基金Shenzhen Science and Technology Innovation Commission(No.JCYJ20230808105700001)Shenzhen University 2035 Program for Excellent Research(No.00000218)。
文摘In thermoelectrics,the manipulation of crystal symmetry is instrumental in optimizing the electrical and thermal transport parameters.Within this context,the present study explored the largely overlooked high-symmetry cubic GeSe,which presented larger band degeneracy than its widely studied medium-symmetry rhombohedral counterpart.We have successfully stabilized cubic Ge Se a ambient conditions through co-alloying with AgSnTe_(2)and Bi.The incorporation of AgSnTe_(2)initiates the transition of GeSe from a low-symmetry orthorhombic to a mediumsymmetry rhombohedral phase,culminating in a highsymmetry cubic structure,underpinned by variation in chemical bonding mechanisms.Notwithstanding this,the persistence of Ag_(2)Te precipitates impedes the total elimination of the residual orthorhombic phase due to the disparate chemical bonding mechanism between Ag_(2)Te and GeSe.Introducing Bi into the rhombohedral-dominated(GeSe)_(0.7)(AgSnTe_(2))_(0.3)matrix leads to the dissolution of Ag_(2)Te precipitates,elimination of the residual orthorhombic phase,and the subsequent stabilization of the exclusive cubic phase.Compared to its orthorhombic counterpart,the cubic GeSe exhibits diminished bandgap and Ge vacancy formation energy,amplified band degeneracy,reduced sound velocity,intensified lattice anharmonicity and multiple phonon scattering centres engendering elevated carrier concentration and density-ofstates effective mass,alongside restrained lattice therma conductivity.Consequently,a peak zT of 0.46 at 573 K is attained for cubic(Ge_(0.7)Bi_(0.3)Se)_(0.7)(AgSnTe_(2))_(0.3),signifying a ninefold increase relative to the initial orthorhombic Ge Se.These results illuminate the critical role of crystal symmetry manipulation in advancing the thermoelectric performance.
基金financially supported by the National Key R&D Program of China(No.2021YFB1507403)the National Natural Science Foundation of China(No.52071218)+1 种基金Shenzhen Science and Technology Innovation Commission(No.JCYJ20230808105700001)Shenzhen University 2035 Program for Excellent Research(No.00000218)。
文摘The successful deployment of thermoelectric materials necessitates the concurrent development of highperformance p-type and n-type pairs situated within an identical matrix.Nevertheless,limiting by the low dopant solubility,the conventional doping often cannot transfer the Fermi level to the opposite carrier type.Here,the solubility limit of donor dopants was enhanced to achieve n-type GeSe by inducing additional cationic vacancies through raising crystal symmetry.Converting the intrinsic p-type nature of GeSe to n-type poses significant challenges,primarily due to the exceedingly low dopant solubility within its native orthorhombic structure.To overcome this,the In_(2)Te_(3)alloying was initially employed to transition GeSe from orthorhombic to rhombohedral structure,simultaneously generating a large number of Ge vacancies.Following this,the introduction of Pb acts to mitigate the excessive Ge vacancies,steering the material toward a weak p-type character.Crucially,the elevated Ge vacancy concentration serves to extend the solubility limit of Bi donor dopant,which not only promotes the formation of cubic phase,but also enables the p-n type transition.As a result,a peak zT of 0.18 at 773 K was attained for the n-type cubic Ge_(0.55)Bi_(0.2)Pb_(0.2)5Se(In_(2)Te_(3))_(0.1),marking an 18-fold enhancement in comparison with its n-type orthorhombic counterpart.This work attests to the efficacy of introducing vacancies through enhancing crystal symmetry as an effective means to expand dopant solubility,thereby offering valuable insights into the achievement of compatible p-and n-type chalcogenides within the same matrix.
基金supported by the National Natural Science Foundation of China(Nos.51971122 and 12174237)Technological Innovation Programs of Higher Education Institutions in Shanxi(No.2021Y440)。
文摘Ge-based selenides have attracted extensive attention as promising candidates for future optoelectronic applications.Despite great progress has been achieved,the controlled synthesis of GeSe2and GeSe nanostructures and understanding the relative growth mechanisms of them are still lacking.Herein,monodispersed GeSe_(2) nanoflowers with a diameter of~4μm and highly uniform GeSe nanoparticles with a lateral size of~100 nm are presented by using a colloidal synthetic method.It is found that borane tert-butylamine complex(TBAB)plays an important role in determining the Ge-Se crystal phases due to its moderately reducibility.Furthermore,the coexistence of GeSe_(2) and GeSe phases can also be acquired by precisely controlling the amount of TBAB.In brief,this work provides both new insights of the phase control of Gebased selenides by liquid-phase method and a practical means of producing well-controlled germanium selenide nanostructures.
文摘GeSe nanosheets were prepared by ultrasonic-assisted liquid<span><span><span style="font-family:;" "=""> </span></span></span><span><span><span><span style="font-family:Verdana;">phase exfoliation (LPE), and the nonlinear saturated absorption performance was experimentally studied. The modulation depth and saturation intensity of the prepared GeSe saturable absorber (SA) were 15% and 1.44 MW/cm</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, respectively. Us</span><span style="font-family:Verdana;">ing the saturated absorption characteristics of GeSe SA, a passively Q-switched </span><span style="font-family:Verdana;">erbium-doped fiber laser was systematically demonstrated. As the pump</span><span style="font-family:Verdana;"> power increases, the pulse repetition frequency increases from 22.8 kHz to 77.59 </span><span style="font-family:Verdana;">kHz. The shortest pulse duration is 1.51 μs, and the corresponding pulse</span><span style="font-family:Verdana;"> energy is 46.14 nJ. Experimental results show that GeSe nanosheets can be used as high-efficiency SA in fiber lasers. Our results will provide a useful reference for demonstrating pulsed fiber lasers based on GeSe equipment.</span></span></span></span>
基金supported by National Natural Science Foundation of China(Grant Nos.61974164,62074166,61804181,62004219,and 6200422).
文摘Selector devices are indispensable components of large-scale memristor array systems.The thereinto,ovonic threshold switching(OTS)selector is one of the most suitable candidates for selector devices,owing to its high selectivity and scalability.However,OTS selectors suffer from poor endurance and stability which are persistent tricky problems for applica-tion.Here,we report on a multilayer OTS selector based on simple GeSe and doped-GeSe.The experimental results show im-proving selector performed extraordinary endurance up to 1010 and the fluctuation of threshold voltage is 2.5%.The reason for the improvement may lie in more interface states which strengthen the interaction among individual layers.These develop-ments pave the way towards tuning a new class of OTS materials engineering,ensuring improvement of electrical perform-ance.
基金supported by Shanghai Academic/Technology Research Leader(Grant No.19XD1421300)the National Natural Science Foundation of China(Grant No.12174060)+3 种基金Program for Professor of Special Appointment(Eastern Scholar TP2019019)the National Key Research and Development Program of China(Grant No.2019YFE0118100)State Key Laboratory of ASIC&System(Grant No.2021MS006)Young Scientist Project of MOE Innovation Platform。
文摘GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity.However,the efficiency of GeSe thin-film solar cells(TFSCs)is still low compared to the Shockley–Queisser limit.Point defects are believed to play important roles in the electrical and optical properties of GeSe thin films.Here,we perform first-principles calculations to study the defect characteristics of GeSe.Our results demonstrate that no matter under the Ge-rich or Se-rich condition,the Fermi level is always located near the valence band edge,leading to the p-type conductivity of undoped samples.Under Se-rich condition,the Ge vacancy(V_(Ge))has the lowest formation energy,with a(0/2–)charge-state transition level at 0.22 eV above the valence band edge.The high density(above 10^(17)cm^(-3))and shallow level of VGeimply that it is the p-type origin of GeSe.Under Se-rich growth condition,Seihas a low formation energy in the neutral state,but it does not introduce any defect level in the band gap,suggesting that it neither contributes to electrical conductivity nor induces non-radiative recombination.In addition,Gei introduces a deep charge-state transition level,making it a possible recombination center.Therefore,we propose that the Se-rich condition should be adopted to fabricate high-efficiency GeSe solar cells.
