Reflectance anisotropy spectroscopy of strain-engineered GaAsBi alloys

Abstract

In this paper we present results obtained by an optical technique, namely Reflectance Anisotropy Spectroscopy (RAS), applied to a series of GaAs1-xBix samples grown by Molecular Beam Epitaxy (MBE) under different strain conditions with increasing concentration of Bi, up to the higher value of about 7%. The epitaxial buffer layers for the growing GaAs1-xBix layer were prepared with either a compressive strain (as it is commonly done) or a tensile strain: the latter case has been proven to be a strategy that allows to obtain a better crystalline quality [E.

Sensing Sub‐Surface Strain in GaAsBi(001) Surfaces by Reflectance Anisotropy Spectroscopy

“…[18,19] In the corresponding anisotropy spectrum measured by RAS (curve c), an evident peak (positive, meaning higher reflectance for polarized light with electric field along the [À110] direction) appears at about 2.5 eV, corresponding to the feature well evident in the low-energy range of all spectra reported in ref. [15]. The amplitude of this peak (about 8 Â 10 À3 ) nicely fits the dependence versus Bi concentration.…”

“…the MBE sample curve presents a lower broadening and is clearly structured (showing an evident LEO oscillation at E 1 and E 1 þ Δ 1 bulk critical points), probably in consequence of a higher and extended long-range order of the grown sample. [15] The importance of optical techniques when applied to MBE-grown GaAsBi alloys is also confirmed through remarkable experiments investigating strain-engineered bismides deposited on thin step-graded InGaAs buffer layers, [35] exploiting the relationships of polarized photoluminescence measurements with the bulk ordering. [36,37] The use of strain-engineering to tune the electronic properties of matter and then customize solid-state materials via a controlled deformation, offers intriguing possibilities to modulate the band structure and consequently ignite new electronic and optical properties, as in 2D materials [38,39] and in quantum dots.…”

“…The amplitude of this peak (about 8 Â 10 À3 ) nicely fits the dependence versus Bi concentration. [15] We have also purposely over-prepared the sample by further annealing at 450 °C for additional 10 min. The LEED pattern (still visible) was degraded, while in the corresponding RAS spectrum the peak amplitude decreased (curve d).…”

“…The Bi-related anisotropy structure (here at 2.44 eV) has the same sign and amplitude as the corresponding structure measured in UHV experiments, confirming that it has not a true surface origin, i.e., it is not related to optical transitions between electronic states of the clean surface (as in GaAs(001), [20,21] InAs(001), [22] C(111)2 Â 1, [24] Si(111)2 Â 1). [4,25] The anisotropy in bulk GaAsBi is due to strain produced by large Bi atoms incorporated in the crystal structure [15] : this is related to well-defined crystal directions, which are the bonds of Bi with neighboring atoms. Such anisotropy is not always visible in the RAS spectra we have measured in UHV.…”

“…We have conclusively demonstrated that it is not due to transitions of the clean surface, but comes from the bulk, due to the insertion of the voluminous Bi atoms: nevertheless, strain is not enough to explain the results. Beyond the phenomenological interpretation [15] a deeper understanding of its origin would be crucial to propose that this spectroscopy becomes a tool to characterize 2D layered materials, as strain induced by the structure has consequences on the electronic properties in low-dimensional systems. [16,17] DOI: 10.1002/pssb.202200237 Reflectance anisotropy spectroscopy (RAS) is applied to study the reconstructed GaAsBi(001) surfaces at room temperature.…”