The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K...The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.展开更多
Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original n...Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original nonradiative multi-phonon(NMP)theory with ab initio calculations.First,we confirmed at the first-principles level that Huang's concise formula gives the same results as the matrix-based formula,and that Huang's high-temperature formula provides an analytical expression for the coupling constant in Marcus theory.Secondly,we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect.The corrected capture rates for defects in GaN and SiC agree well with experiments.展开更多
为了快速判别稀土掺杂晶体材料的上转换发光能力,设计并采用液–固相转移法合成Yb^(3+)/Er^(3+)双掺MLuxFy(M为Li、Na、K、Rb或Cs;x=1,y=4或x=2,y=7)材料体系,使用X射线衍射仪、透射电镜、拉曼光谱仪和荧光分光光度计对材料体系进行结...为了快速判别稀土掺杂晶体材料的上转换发光能力,设计并采用液–固相转移法合成Yb^(3+)/Er^(3+)双掺MLuxFy(M为Li、Na、K、Rb或Cs;x=1,y=4或x=2,y=7)材料体系,使用X射线衍射仪、透射电镜、拉曼光谱仪和荧光分光光度计对材料体系进行结构和发光性能检测。实验结果表明,Yb^(3+)/Er^(3+)双掺MLuxFy亚微米/纳米晶体在980 nm激光激发下均可实现绿色和红色上转换发光,但其上转换发光能力各不相同。实验中,利用泵浦功率阈值(pump power threshold,PPT)快速区分Yb^(3+)/Er^(3+)双掺亚微米/纳米晶体的上转换发光能力。通过分析发现,PPT与Yb^(3+)/Er^(3+)双掺亚微米/纳米晶体的最大声子能量之间存在相关性。因此,在稀土掺杂上转换发光晶体材料的筛选过程中,可在发光性能测试时使用PPT,以快速判别其上转换发光能力。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12374013)the Fundamental Research Funds for the Central Universities(Grant No.2020SCUNL107).
文摘The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.
基金supported by the National Natural Science Foundation of China (Grand Nos. 61927901, 11674241, 11574304, and 11774338)supported by the Director, Office of Science (SC), Basic Energy Science (BES)/Materials Science and Engineering Division (MSED) of the US Department of Energy (DOE) (Grant No. DE-AC02-05CH11231) through the Theory of Material project
文摘Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original nonradiative multi-phonon(NMP)theory with ab initio calculations.First,we confirmed at the first-principles level that Huang's concise formula gives the same results as the matrix-based formula,and that Huang's high-temperature formula provides an analytical expression for the coupling constant in Marcus theory.Secondly,we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect.The corrected capture rates for defects in GaN and SiC agree well with experiments.
文摘为了快速判别稀土掺杂晶体材料的上转换发光能力,设计并采用液–固相转移法合成Yb^(3+)/Er^(3+)双掺MLuxFy(M为Li、Na、K、Rb或Cs;x=1,y=4或x=2,y=7)材料体系,使用X射线衍射仪、透射电镜、拉曼光谱仪和荧光分光光度计对材料体系进行结构和发光性能检测。实验结果表明,Yb^(3+)/Er^(3+)双掺MLuxFy亚微米/纳米晶体在980 nm激光激发下均可实现绿色和红色上转换发光,但其上转换发光能力各不相同。实验中,利用泵浦功率阈值(pump power threshold,PPT)快速区分Yb^(3+)/Er^(3+)双掺亚微米/纳米晶体的上转换发光能力。通过分析发现,PPT与Yb^(3+)/Er^(3+)双掺亚微米/纳米晶体的最大声子能量之间存在相关性。因此,在稀土掺杂上转换发光晶体材料的筛选过程中,可在发光性能测试时使用PPT,以快速判别其上转换发光能力。
