Computational and experimental imaging of Mn defects on GaAs (110) cross-sectional surfaces

We present a combined experimental and computational study of the (110) cross-sectional surface of Mn $\delta$-doped GaAs samples. We focus our study on three different selected Mn defect configurations not previously studied in detail, namely surface interstitial Mn, isolated and in pairs, and substitutional Mn atoms on cationic sites $\left({\mathrm{Mn}}_{\mathrm{Ga}}\right)$ in the first subsurface layer. The sensitivity of the scanning tunneling microscopy (STM) images to the specific local environment allows us to distinguish between Mn interstitials with nearest-neighbor As atoms $\left({\mathrm{Int}}_{\mathrm{As}}\right)$ rather than Ga atoms $\left({\mathrm{Int}}_{\mathrm{Ga}}\right)$, and to identify the fingerprint of peculiar satellite features around subsurface substitutional Mn. The simulated STM maps for ${\mathrm{Int}}_{\mathrm{As}}$, both isolated and in pairs, and ${\mathrm{Mn}}_{\mathrm{Ga}}$ in the first subsurface layer are consistent with some experimental images hitherto not fully characterized.

Figure 1

(a) Experimental (110) XSTM image of a 0.2 monolayer Mn $\delta$-doped layer in GaAs at a sample bias voltage of $1.7\mathrm{eV}$. This image has not been corrected for the drift of the sample. (b) XSTM image of a Mn related structure at the bias voltage of $-1.4\mathrm{eV}$ (left) and $+1.9\mathrm{eV}$ (right). The white lines show the [001] Ga atomic rows.

Figure 2

Isolated Mn interstitial dopants on GaAs(110) surface, with As nearest neighbors (${\mathrm{Int}}_{\mathrm{As}}$, left-hand side) and Ga nearest neighbors (${\mathrm{Int}}_{\mathrm{Ga}}$, right-hand side). Upper panels: ball-and-stick model of the relaxed surface, top and side view. Only the three topmost layers are shown in the side view. Black spheres are Mn, white spheres are As, grey spheres are Ga. Lower panels: simulated XSTM images at occupied states and empty states, respectively, for different bias voltages.

Figure 3

Smaller superimposed panel: simulated XSTM image of a pair of ${\mathrm{Int}}_{\mathrm{As}}$ on GaAs(110) surface with a relative distance of $\sim 8\mathrm{\AA }$ along the [110] direction at a bias voltage $V_b=–2\mathrm{V}$. The larger panel shows an experimental image compatible with the simulation.

Figure 4

Upper smaller superimposed panels simulated XSTM image of a subsurface ${\mathrm{Mn}}_{\mathrm{Ga}}$ on GaAs(110) at negative (left-hand side) and positive (right-hand side) bias voltages. The lower panels show corresponding experimental images of the structure $B$ [see Fig. 1a] taken at sample bias voltages of $-1.4\mathrm{V}$ (left-hand side) and $+1.8\mathrm{V}$ (right-hand side) that are compatible with the simulations, performed with voltages of $-1\mathrm{V}$ and $+1\mathrm{V}$.