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

Abstract

Reflectance anisotropy spectroscopy (RAS) is applied to study the reconstructed GaAsBi(001) surfaces at room temperature. Arsenic‐capped GaAsBi samples with 7% Bi concentration are grown by molecular beam epitaxy (MBE) in nearly matched conditions on a proper buffer layer and annealed in ultra‐high vacuum (UHV). Low energy electron diffraction (LEED) shows that, following the As decapping, a 2 × 3/1 × 3 phase (Bi‐rich) is obtained after annealing the sample at 400 °C, while subsequent annealing at 450 °C yields a deterioration of the surface order. RAS spectra measured in situ allow to definitely confirm that the characteristic Bi‐dependent anisotropy measured below 2.5 eV has not a true surface origin, although being connected to the surface: it is related to the strain of the directional bonds between Bi atoms existing at the surface and below the surface. This result has a twofold significance: it recommends that previous attributions to the surface of RAS anisotropy features in III–V semiconductors should be in some cases revisited; for the future, it shows that RAS is suitable to characterize 2D‐layered materials, and to investigate the consequences of strain in the electronic properties of low‐dimensional systems.

Understanding Growth‐Faulted GaAsBi Samples by Reflectance Anisotropy Spectroscopy

“…For details about the growth and the samples, see text and refs. [33,34]. All the spectra have been measured in air.…”

“…[40][41][42] However, all the curves presented in this work have been measured ex situ in ambient atmosphere, i.e., are related to bulk anisotropies. [33,34] The background anisotropy-measured on an oxidised Si(001) sample-has been subtracted in all cases. For all the spectra reported in figures, we have drawn the corresponding "zero line".…”

“…real-time application, as they can monitor the growth process without moving the sample from its position in front of the effusion cells of the reactor or of the MBE flange. [32][33][34] This in principle offers the facility of a real-time correction of the growth process during deposition due to, e.g., change of fluxes, wrong substrate temperature, excess of Bi, although to our knowledge this, in the case of RAS, has been never reported in literature.…”

“…RAS-applied, in the case of GaAsBi, to (001) oriented samples-exploits the particular anisotropy due to the insertion of Bi atoms in the otherwise isotropic GaAs bulk, resulting in a characteristic feature at about or below 2.5 eV (the energy position is slightly varying from sample to sample), whose amplitude has been demonstrated to be linearly dependent upon the Bi density, while the sign (positive/negative meaning higher reflectance for the light electric field polarized along the [À110]/[110] direction) is related to the strain, tensile or compressive, induced by the substrate. [33,34] Two previous papers were dedicated to the characteristic RAS spectra measured on high-quality GaAsBi samples, for different growth conditions and at increasing values of Bi density. A characteristic, well-defined anisotropy signal below 2.5 eV has been demonstrated to be connected to the presence of Bi and in particular to the strain produced in the subsurface region by the voluminous Bi atoms.…”

“…RAS—applied, in the case of GaAsBi, to (001) oriented samples—exploits the particular anisotropy due to the insertion of Bi atoms in the otherwise isotropic GaAs bulk, resulting in a characteristic feature at about or below 2.5 eV (the energy position is slightly varying from sample to sample), whose amplitude has been demonstrated to be linearly dependent upon the Bi density, while the sign (positive/negative meaning higher reflectance for the light electric field polarized along the [−110]/[110] direction) is related to the strain, tensile or compressive, induced by the substrate. [ 33,34 ]…”