Calculation shown that the refraction index of Ge_0.6Si_0.4/Sistrained-layer superlattice n≈3.64, when L_w=9 nm and L_b=24 nm. Analgorithm of numerical iteration for effective refraction index isemployed to obtain di...Calculation shown that the refraction index of Ge_0.6Si_0.4/Sistrained-layer superlattice n≈3.64, when L_w=9 nm and L_b=24 nm. Analgorithm of numerical iteration for effective refraction index isemployed to obtain different effective refraction indexes atdifferent thickness (L). As a result, the thickness ofGe_0.6Si_0.4/Si strained-layer superlattice optical waveguide, L≤363nm, can be determined, which is very important for designingwaveguide devices. An optical waveguide can be made into a nanometerdevice by using Ge_0.6 Si_0.4/Si strained-layer superlattice.展开更多
The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties.Under different biaxial mismatch strains,ferroelectric superlattices exhibit different domain s...The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties.Under different biaxial mismatch strains,ferroelectric superlattices exhibit different domain structures and electromechanical coupling properties.A three-dimensional phase field model is employed to investigate the detailed domain evolution and electromechanical properties of the PbTiO_(3)/SrTiO_(3)(PTO/STO)superlattices with different biaxial mismatch strains.The phase field simulations show that the ferroelectric superlattice exhibits large electrostrain in the stacking direction when an external field is applied.Under a large compressive mismatch strain,vortex domains appear in ferroelectric layers with the thickness of 4 nm.The vortex domains become stable cdomain under a large external electric field,which remains when the electric field is removed.When the initial compressive mismatch strain decreases gradually,the waved or a1/a2 domains replaces the initial vortex domains in the absence of electric field.The fully polarized c-domain by a large electric field switches to diagonal direction domain or a/c domain when the electric field is small.Furthermore,when a biaxial tensile strain is applied to the superlattice,ferroelectric domains switch back to the initial a1/a2 twin-like domain structure,resulting in the recoverable and large electrostrain.This provides an effective way to obtain the large and recoverable electrostrain for the engineering application.展开更多
We investigate the growth of InP-on-GaAs combined with the advantages of double low-temperature （LT） buffers and strained layer surperlattices （SLSs）. It is found that LT-InP/LT-GaAs double LT buffers are more eff...We investigate the growth of InP-on-GaAs combined with the advantages of double low-temperature （LT） buffers and strained layer surperlattices （SLSs）. It is found that LT-InP/LT-GaAs double LT buffers are more effective for strain accommodation than a LT-InP single buffer in InP-on-GaAs. On the other hand, there is an optimal thickness for LT-GaAs for a given thickness of the LT-InP layer,at which the double LT buffers can reach the best state for strain ad- justment. Furthermore,the position of insertion of SLSs should be carefully designed because the distance above the InP/ buffer interface plays an important role in threading dislocation interactions for dislocation reduction. As a result, the density of threading dislocations in the InP epilayer is markedly reduced. X-ray diffraction measurements show that the full width at half maximum of the ω/2θ rocking curve for the 2μm-thick InP epilayer is less than 200.展开更多
文摘Calculation shown that the refraction index of Ge_0.6Si_0.4/Sistrained-layer superlattice n≈3.64, when L_w=9 nm and L_b=24 nm. Analgorithm of numerical iteration for effective refraction index isemployed to obtain different effective refraction indexes atdifferent thickness (L). As a result, the thickness ofGe_0.6Si_0.4/Si strained-layer superlattice optical waveguide, L≤363nm, can be determined, which is very important for designingwaveguide devices. An optical waveguide can be made into a nanometerdevice by using Ge_0.6 Si_0.4/Si strained-layer superlattice.
基金supported by the National Natural Science Foundation of China(Nos.11672264,11972320)the Zhejiang Provincial Natural Science Foundation(No.LZ17A020001)。
文摘The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties.Under different biaxial mismatch strains,ferroelectric superlattices exhibit different domain structures and electromechanical coupling properties.A three-dimensional phase field model is employed to investigate the detailed domain evolution and electromechanical properties of the PbTiO_(3)/SrTiO_(3)(PTO/STO)superlattices with different biaxial mismatch strains.The phase field simulations show that the ferroelectric superlattice exhibits large electrostrain in the stacking direction when an external field is applied.Under a large compressive mismatch strain,vortex domains appear in ferroelectric layers with the thickness of 4 nm.The vortex domains become stable cdomain under a large external electric field,which remains when the electric field is removed.When the initial compressive mismatch strain decreases gradually,the waved or a1/a2 domains replaces the initial vortex domains in the absence of electric field.The fully polarized c-domain by a large electric field switches to diagonal direction domain or a/c domain when the electric field is small.Furthermore,when a biaxial tensile strain is applied to the superlattice,ferroelectric domains switch back to the initial a1/a2 twin-like domain structure,resulting in the recoverable and large electrostrain.This provides an effective way to obtain the large and recoverable electrostrain for the engineering application.
文摘We investigate the growth of InP-on-GaAs combined with the advantages of double low-temperature （LT） buffers and strained layer surperlattices （SLSs）. It is found that LT-InP/LT-GaAs double LT buffers are more effective for strain accommodation than a LT-InP single buffer in InP-on-GaAs. On the other hand, there is an optimal thickness for LT-GaAs for a given thickness of the LT-InP layer,at which the double LT buffers can reach the best state for strain ad- justment. Furthermore,the position of insertion of SLSs should be carefully designed because the distance above the InP/ buffer interface plays an important role in threading dislocation interactions for dislocation reduction. As a result, the density of threading dislocations in the InP epilayer is markedly reduced. X-ray diffraction measurements show that the full width at half maximum of the ω/2θ rocking curve for the 2μm-thick InP epilayer is less than 200.
