Connections between local and macroscopic properties in solids: The case of N in III-V-N alloys

Although it is well known that dilute species often significantly modify the properties of solids in which they are hosted, a basic question remains open: How critical are their local properties in determining the macroscopic ones of the host material? Here we address this issue by taking N in dilute III-V-N alloys as a paradigmatic case and propose an original approach based on synergic progress in x-ray spectroscopies, density functional theory simulations, and hydrogen exposure as a tool to modify local bonding. In this way we are able to clarify how local properties operate by identifying the coupling mechanism between specific atomic orbitals responsible for the changes of both deep and band edge states. The success of our approach indicates a new way to connect local and macroscopic properties.

Figure 1

Top: experimental XES and XAS spectra at the N $K$ edge of as-grown (black dash-dotted lines) and H irradiated (red continuous lines) samples. The shaded areas in the top panel mark the value of the gap for as-grown (light gray) and the blue shift induced by H irradiation (dark red). Bottom: Ab initio FMS and DFT simulations of XAS and XES spectra for GaAsN and the C${}_{2v}$-2H complex.

Figure 2

$s$ and $p$ state VB DOSs projected on N and its four Ga neighbors calculated by HSE-DFT. The insets illustrate the local geometries; N, Ga, and H atoms are represented by medium (blue), large (purple), and small (gray) circles, respectively and distances are given in Å. In GaAs, the Ga-As distance is 2.44 Å.

Figure 3

Top: Total DOSs for GaAs, GaAsN, and the C${}_{2v}$-2H complex. The middle and bottom panels report the total and projected DOSs on N for GaAsN and for the C${}_{2v}$-2H complex, respectively. The insets report a magnified view of the band edge regions.

Figure 4

Contour plots of the square modulus of the electron wave function corresponding to the CBM calculated at the Γ point for: (a) GaAs, (b) GaAsN, and (c) the C${}_{2v}$-2H complex. Wave function sampling was 3.5 × 10${}^{-4}$ electrons/(a.u.)³ in (a) and 1 × 10${}^{-3}$ electrons/(a.u.)³ for (b) and (c). Ga, As, N, and H atoms are indicated by purple, yellow, blue, and light blue spheres, respectively. The N atom (partially hidden by the isosurfaces) is at the center of (b) and is bonded to two H atoms in (c).