Infrared Optical And Polarization Properties Study In GaAs(Sb,Bi) Bulk Semiconductors And Nanowires

In recent decades,III-V semiconductor,e.g.GaAs（Sb,Bi）,have currently gained considerable research interest owing to excellent optical and electronic properties such as direct band-gap,high electron mobility and small effective mass of electrons.By carefully tuning alloy composition,the emission energy can be precisely tailored to cover two common optical window of 1.3μm and 1.55μm for fiber-optic communication.These properties make GaAs（Sb,Bi）a promising material for high-speed and low-power electronic devices,near-infrared photon detector and near-infrared semiconductor laser.Moreover,a strong increase of spin-orbit interaction is expected in GaAs（Sb,Bi）following incorporation of heavy element Sb（Bi）,which may prove useful for spintronic devices utilizing low modulation electric field.In this paper,we mainly focus on infrared optical and polarization properties of bulk GaAs_0.44Sb_0.56 and GaAs（Bi）nanowires.Details are as follows:（1）We designed and built an micro Raman and Photoluminescence measurement systems with polarized,picosecond temporal and sub-micron spatial resolution.What’s more,a modified optics based technique was developed to effectively suppress spurious background signals encountered in the photoreflectance（PR）spectra obtained from bulk semiconductors and semiconductor microstructures.Based on a traditional PR setup,the novel PR approach utilized an achromatic beam reduction system to narrow the profile of a probe beam,which was subsequently collected by a focus lens coupled with an iris.The new setup guarantees high collection efficiency for probe signals and strong suppression of background signals.Compared with existing PR methods for background minimization,the proposed PR technique is simpler to accomplish,more cost effective,and provides a higher signal-to-noise ratio for the PR spectra.（2）The effect of the thermal annealing on the optical and spin properties in GaAs_0.44Sb_0.56 epilayers grown on InP was investigated via photoreflectance,power-dependent and time-resolved photoluminescence spectroscopy as well as optical orientation measurement.The carrier’s localization and the optical spin detection efficiency increase with an increase of annealing temperature up to 600°C.The enhancement of the spin detection efficiency is attributed to both the shortening of the electron lifetime and the prolonging of the spin lifetime as a result of the enhanced carriers’localization induced by the annealing process.Our results provided an approach to enhance spin detection efficiency of GaAsSb with its PL emission in the 1.55μm region.（3）GaAs（Bi）nanowires（NWs）were synthesized by Au-assisted molecular beam epitaxy.Bi incorporation results in a transition of crystal phase in GaAs NWs from 2H to 4H polytype.Polarized Raman spectra clearly show that an A₁ phonon mode at²57.6 cm^-1 arising from TO（A1）branch at the L point of Brillouin zone of ZB structure,become active in（,）?geometry in 4H polytype.The red shift observed in low temperatureμ-PL spectra of GaAs Bi NWs is attributed to 4H crystal structure and Bi-introduction induced alloy effects.The observed orthogonal polarization in PL emission of GaAsBi NW coincides withΓ₉ heavy hole symmetry predicted by theoretical calculation.Moreover,incorporation of Bi into GaAs also significantly reduce the temperature sensitivity of bandgap in GaAsBi NWs,advantageous for future optoelectronics applications.