Photoluminescence peculiarities in InGaAs/GaAs structures with different InAs quantum dot densities

Emission peculiarities and X-ray diffraction (XRD) have been studied in GaAs/InGaAs/GaAs quantum wells (QWs) with different densities of embedded InAs quantum dots (QDs). The QD density decreased from 1.1×10¹¹ to 1.3×10¹⁰ cm^-2 when the QD growth temperature was increased from 470 up to 535 °C. The QD density changes are accompanied by the nonmonotonic variation of the photoluminescence (PL) intensity and peak positions: the highest PL intensity corresponds to lowest emission energy (1.3 μm) in InAs QDs obtained at the QD density equal to 3.4×10¹⁰ cm^-2. PL temperature dependences have been studied in the range of 10-300 K with the aim to analysis the QD band gap shrinkage. It revealed the process of In/Ga intermixing that is characterized by nonmonotonic behavior versus QD growth temperatures and QD densities. The XRD study has revealed high intensity peaks related to the diffraction of X-ray beam from (4 0 0) crystal planes in the cubic GaAs QW layers and GaAs substrates. It was shown that (4 0 0) diffraction peaks in GaAs QW layers shift to high angles, in comparison with the GaAs substrate, testifying the compression strain. The strain value in GaAs QW layers has been estimated and it is revealed that this value changes nonmonotonic with InAs QD density and its minimum corresponds to a QD density of 3.4×10¹⁰ cm^-2. It is shown that In/Ga intermixing is stimulated by the compression strains: higher level of strains provokes higher In/Ga intermixing. Therefore, the shift of PL peak positions in InAs QDs versus QD density and size is the result of the influence of three factors: the quantum confined effect in QDs of different sizes, In/Ga intermixing, and the compression strain. The value of PL peak shift owing to the compression strains in QWs has been estimated as well. Physical reasons for the nonmonotonic variation of PL and strains in InGaAs/GaAs QWs versus InAs QD density have been discussed.