Abstract
Self-catalyzed growth of axial GaAs1−xSbx nanowire (NW) arrays with bandgap tuning corresponding to the telecommunication wavelength of 1.3 µm poses a challenge, as the growth mechanism for axial configuration is primarily thermodynamically driven by the vapor-liquid-solid growth process. A systematic study carried out on the effects of group V/III beam equivalent (BEP) ratios and substrate temperature (Tsub) on the chemical composition in NWs and NW density revealed the efficacy of a two-step growth temperature sequence (initiating the growth at relatively higher Tsub = 620 °C and then continuing the growth at lower Tsub) as a promising approach for obtaining high-density NWs at higher Sb compositions. The dependence of the Sb composition in the NWs on the growth parameters investigated has been explained by an analytical relationship between the effective vapor composition and NW composition using relevant kinetic parameters. A two-step growth approach along with a gradual variation in Ga-BEP for offsetting the consumption of the droplets has been explored to realize long NWs with homogeneous Sb composition up to 34 at.% and photoluminescence emission reaching 1.3 µm at room temperature.
Highlights
The one-dimensional (1D) architecture of nanowires (NWs) enables high tolerance of lattice mismatched heterostructures, sub-wavelength optical phenomena, and quantum size effects[1,2,3] When combined with an ability to integrate with other nanoscale and microscale devices, 1D NWs provide the ability to fabricate optoelectronic devices with distinct properties
The organization of this section is as follows: effects of V/III beam equivalent pressure (BEP) ratio and substrate temperature variation on NW density and composition, discussion of these results using analytical formulation of constituents and vapor composition, followed by systematic study of the two-step growth process using a variety of characterization techniques
From the comprehensive and systematic study of the MBE growth of GaAsSb NWs in the axial configuration as a function of constituent growth flux and substrate temperature, we have demonstrated that the challenge of rapid consumption of the Ga melt at the tip by the excess group V flux at higher Sb concentration can be overcome by a two-step growth process with gradual variation of the Ga supply during axial growth
Summary
Estiak Ahmad[1], Md Rezaul Karim 1, Shihab Bin Hafiz[1], C Lewis Reynolds3,Yang Liu3 & Shanthi Iyer 1,2. Among nanowires of different semiconductor material systems, the bandgap of GaAs1−xSbx covers the important wavelength range from 870 nm (GaAs) to 1700 nm (GaSb), which has potential applications in generation optoelectronic devices, namely solar cells, optical telecommunications, photonic integrated circuits and quantum information science[4,5,6,7,8] They belong to the class of Sb-based III-V compound semiconductor NWs with favorable optoelectronic characteristics, namely high optical absorption and superior carrier mobility. Bandgap tuning corresponding to the desirable wavelength of 1.3 μm in the telecommunication window has been demonstrated[10, 11] with a core-shell configuration These nanowires suffer from a high density of planar defects with detrimental impact on the optoelectronic quality of the NWs. In contrast, axially configured GaAsSb NWs yield nearly planar-defect-free nanowires due to the predominance of the thermodynamically driven vapor-liquid-solid. We present in this work a study of the two-step growth temperature approach in conjunction with Ga variation during the growth, using a variety of characterization techniques, to attain NWs of good compositional homogeneity with PL emission reaching 1.3 μm
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