The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth condi...The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth conditions on E2 （TO）, E1 （TO） and A1 （LO） phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E2 （TO） modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E2 （TO） mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A1 （longitudinal optical plasma coupling （LOPC）） mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A1 （LOPC） mode in 4H-SiC.展开更多
Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the ...Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the wavelength of 800hm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.展开更多
Structural properties of InxGa_(1−x)N/GaN multi-quantum wells(MQWs)grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction(SRXRD),Rutherford backscatter...Structural properties of InxGa_(1−x)N/GaN multi-quantum wells(MQWs)grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction(SRXRD),Rutherford backscattering/channelling(RBS/C)and high-resolution transmission electron microscopy.The sample consists of eight periods of InxGa_(1−x)N/GaN wells of 2.1 nm thickness and 8.5 nm thickness of GaN barrier,and the results are very close,which verifies the accuracy of the three methods.The indium content in InxGa_(1−x)N/GaN MQWs by SRXRD and RBS/C is estimated,and results are in general the same.By RBS/C random spectra,the indium atomic lattice substitution rate is 94.0%,indicating that almost all indium atoms in InxGa_(1−x)N/GaN MQWs are at substitution,that the indium distribution of each layer in InxGa_(1−x)N/GaN MQWs is very homogeneous and that the InxGa_(1−x)N/GaN MQWs have a very good crystalline quality.It is not accurate to estimate indium content in InxGa_(1−x)N/GaN MQWs by photoluminescence(PL)spectra,because the result from the PL experimental method is very different from the results by the SRXRD and RBS/C experimental methods.展开更多
为了研究In Al N材料的光学参数随温度的变化特性,采用变温椭圆偏振光谱(25～600℃)测量技术对In Al N合金材料在193～1 650 nm宽光谱范围内进行了表征。利用Tauc-Lorentz振子模型描述和拟合变温椭偏光谱测量数据,得到了In Al N薄膜的...为了研究In Al N材料的光学参数随温度的变化特性,采用变温椭圆偏振光谱(25～600℃)测量技术对In Al N合金材料在193～1 650 nm宽光谱范围内进行了表征。利用Tauc-Lorentz振子模型描述和拟合变温椭偏光谱测量数据,得到了In Al N薄膜的光学常数(n、k和α)随温度的变化曲线。由变化曲线可见,在温度50～600℃,光学带隙从4. 56 e V减小到4. 35 e V,折射率峰值对应的能量则从4. 61 e V减小到4. 37 e V。两者都随温度升高而减小,其变化规律符合Varshni方程的预期。结果表明,在600℃以下测试温度条件下,In Al N合金材料的光谱和光学参数没有发生突变,说明In Al N合金材料具有高的热稳定性,并未发生影响材料光学性能的晶体结构变化。展开更多
基金National Natural Science Foundation of China(61367004,11604058)Guangxi Key Laboratory for Relativistic Astrophysics-Guangxi Natural Science Creative Team funding(2013GXNSFFA019001)Guangxi Natural Science Foundation(2016GXNSFBA380244)
基金Supported by the National Natural Science Foundation of China under Grant Nos 61176085,11474365 and 61377055the Department of Education of Guangdong Province under Grant No gjhz1103the Open-Project Program of the State Key laboratory of Opto-Electronic Material and Technologies of Sun Yatsen University
文摘The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth conditions on E2 （TO）, E1 （TO） and A1 （LO） phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E2 （TO） modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E2 （TO） mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A1 （longitudinal optical plasma coupling （LOPC）） mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A1 （LOPC） mode in 4H-SiC.
基金an open-project fund support from the State Key laboratory of Opto-Electronic Material and Technologies (Sun Yat-sen University),Guangzhou,Chinasupported by NTU Excellent Research Project (10R80908 and 102R890954)
基金Supported by the National Natural Science Foundation of China under Grant Nos 10674031 and 60978055, the National Taiwan University under Grant Nos NSC-97-2221-E-002-026 and NSC-98-2221-E-002-015-MY3, and the NSF of USA through the Center of Physics and Chemistry of Materials under Grant No HRD-0420516.
文摘Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the wavelength of 800hm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.
基金by the National Natural Science Foundation of China under Grant No 10875004 and 11005005the National Basic Research Program of China under Grant No 2010CB832904.
文摘Structural properties of InxGa_(1−x)N/GaN multi-quantum wells(MQWs)grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction(SRXRD),Rutherford backscattering/channelling(RBS/C)and high-resolution transmission electron microscopy.The sample consists of eight periods of InxGa_(1−x)N/GaN wells of 2.1 nm thickness and 8.5 nm thickness of GaN barrier,and the results are very close,which verifies the accuracy of the three methods.The indium content in InxGa_(1−x)N/GaN MQWs by SRXRD and RBS/C is estimated,and results are in general the same.By RBS/C random spectra,the indium atomic lattice substitution rate is 94.0%,indicating that almost all indium atoms in InxGa_(1−x)N/GaN MQWs are at substitution,that the indium distribution of each layer in InxGa_(1−x)N/GaN MQWs is very homogeneous and that the InxGa_(1−x)N/GaN MQWs have a very good crystalline quality.It is not accurate to estimate indium content in InxGa_(1−x)N/GaN MQWs by photoluminescence(PL)spectra,because the result from the PL experimental method is very different from the results by the SRXRD and RBS/C experimental methods.
文摘为了研究In Al N材料的光学参数随温度的变化特性,采用变温椭圆偏振光谱(25～600℃)测量技术对In Al N合金材料在193～1 650 nm宽光谱范围内进行了表征。利用Tauc-Lorentz振子模型描述和拟合变温椭偏光谱测量数据,得到了In Al N薄膜的光学常数(n、k和α)随温度的变化曲线。由变化曲线可见,在温度50～600℃,光学带隙从4. 56 e V减小到4. 35 e V,折射率峰值对应的能量则从4. 61 e V减小到4. 37 e V。两者都随温度升高而减小,其变化规律符合Varshni方程的预期。结果表明,在600℃以下测试温度条件下,In Al N合金材料的光谱和光学参数没有发生突变,说明In Al N合金材料具有高的热稳定性,并未发生影响材料光学性能的晶体结构变化。
