Strain compensation technique in self-assembled InAs/GaAs quantum dots for applications to photonic devices

We report the strain compensation (SC) technique for a stacked InAs/GaAs self-assembled quantum dot (QD) structure grown by metalorganic chemical vapour deposition (MOCVD). Several techniques are used to investigate the effect of the SC technique: the high-resolution x-ray diffraction (XRD) technique is used to quantify the reduction in overall strain, atomic force spectroscopy is used to reveal that the SC layer improves the QD uniformity and reduces the defect density and photoluminescence characterization is used to quantify the optical property of stacked InAs QDs. In addition, experimental and mathematical evaluation of reduction in the strain field in the compensated structure is conducted. We identify two types of strain in stacked QD samples, homogeneous and inhomogeneous strain. XRD spectra indicate that vi > 36% reduction in the homogeneous strain can be accomplished. Inhomogeneous strain field is investigated by studying the strain coupling probability as a function of the spacer thickness, indicating that 19% reduction in inhomogeneous strain within SC structures has been evaluated. Next, device application of SC techniques including lasers and modulators is reported. Room temperature ground-state lasing from 6-stack InAs QDs with GaP SC is realized at a lasing wavelength of 1265?nm with a threshold current density of 108?A?cm?2. The electro-optic (EO) properties of 1.3??m self-assembled InAs/GaAs QDs are investigated. The linear and quadratic EO coefficients are 2.4 ? 10?11?m?V?1 and 3.2 ? 10?18?m2?V?2, respectively, which are significantly larger than those of GaAs bulk materials. Also, the linear EO coefficient is almost comparable to that of lithium niobate.