Optical properties of GaAs 1-x Bi x /GaAs quantum well structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates

In this work, the electronic bandstructure of GaAs 1-x Bi x /GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 ? x ? 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C BiM ) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively. © 2018 IOP Publishing Ltd. Fundação de Amparo à Pesquisa do Estado de São Paulo: 14/ 50513-7, 16/10668-7 Firat University Scientific Research Projects Management Unit: FYD-2016-20128, ONAP-52321 115F063 Academy of Finland: 259111 695116 European Research Council This work was partially supported by the Scientific Research Projects Coordination Unit of Istanbul University (ONAP-52321 and FYD-2016-20128) and supported by The Scientific and Technical Research Council of Turkey (TUBITAK) under Grant No. 115F063. YGG acknowledges the financial support from FAPESP ( grants numbers 16/10668-7 and 14/ 50513-7). JP, JH and MC acknowledge the financial support from European Research Council (ERC AdG AMETIST, #695116) and the Academy of Finland (TransPhoton, #259111).