Analysis of InAs(001) surfaces by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) was applied to study the reconstructed surfaces of InAs(001) at room temperature. Arsenic-capped InAs samples, grown by molecular beam epitaxy, were annealed in ultrahigh vacuum. Low energy electron diffraction shows that, following As decapping, a $2\times 4$ phase (As-rich) is obtained after annealing the sample at 340 °C (10 mins), while a subsequent annealing at 450 °C (15 mins) yields a $4\times 2$ phase (In-rich). Using Kramers-Kronig relations, the anisotropy of the imaginary part of the surface dielectric function $\left(\Delta {\varepsilon }_s^{″}\right)$ between [1¯10] and [110] directions of the substrate has been obtained from RAS data. We present both the RAS and $\Delta {\varepsilon }_s^{″}$ spectra characteristic of $(2\mathrm{}\times 4)$ and $(4\mathrm{}\times 2)$ reconstructed InAs(001) surfaces, and interpret the appearing features in terms of surface-state transitions and bulk transitions (modified by the surface). The experimental data are compared with the case of GaAs(001). Below 3 eV, the presence of As and In dimers at the surface gives rise to optical anisotropies centered at 2.4 and 1.7 eV, respectively, with opposite polarizations depending on the dimer-bond direction. At higher energies, a structure related to $E_0^{\prime }$ bulk critical point (at 4.4 eV) is visible.