Local structure of nitrogen-hydrogen complexes in dilute nitrides

We have investigated the structure of nitrogen-hydrogen complexes in ${\text{GaAs}}_{1-y}{\text{N}}_y$ and ${\text{In}}_x{\text{Ga}}_{1-x}{\text{As}}_{1-y}{\text{N}}_y$ dilute nitride alloys by performing x-ray absorption near-edge structure spectroscopy (XANES). We simulated the spectra based on first-principles calculations of the most recent defective structures proposed in the literature for hydrogenated materials. The comparison between the experimental data and simulations allows us to clarify that the core of the defect is a complex with ${\text{C}}_{2v}$ structure in the neutral charge state, in agreement with the expansion of the lattice parameter measured by x-ray diffraction. Our results are compatible with the presence of H satellites bound to neighboring Ga atoms but not with complexes involving more than two H atoms bound to the same N. Nevertheless, we were not able to determine uniquely the number of H satellites, which may depend on growth conditions. Strain related to the epitaxial growth has a very little effect on the XANES spectra.

Figure 1

(Color online) Sketch of the different N-H complexes under investigation.

Figure 2

(Color online) (a) HRXRD (004) rocking curves for the ${\text{GaAs}}_{0.9878}{\text{N}}_{0.0122}$ epilayer before deuteration (bottommost line), after deuteration (middle line, sample A), and after deuteration followed by a mild thermal annealing at $250°\text{C}$ (topmost line, sample B); (b) corresponding PL spectra.

Figure 3

(Color online) (a) HRXRD (004) rocking curves for a ${\text{In}}_{0.037}{\text{Ga}}_{0.963}{\text{As}}_{0.9657}{\text{N}}_{0.0343}$ epilayer with $x=3.70\%$ and $y=3.43\%$ before hydrogenation (bottommost curve), after hydrogenation (topmost curve, sample C), and for a piece of epilayer undertaking the same annealing procedure as during hydrogenation but with the H source switched off (middle curve); (b) corresponding PL spectra.

Figure 4

(Color online) N $K$-edge XANES simulations for selected N-H complexes having an asymmetric ${\text{C}}_{2v}$ core and for ${\text{N-H}}_3$ complexes (continuous line) compared to three experimental spectra (dots, at the bottom); a very small energy shift of $-0.25\text{eV}$ is applied to all simulations for a better matching with the experimental data.

Figure 5

(Color online) N $K$-edge XANES simulations (continuous line) for pure ${\text{GaAs}}_{1-y}{\text{N}}_y$, monohydrogen bond-centered complexes $\left({\text{N-H}}_{\text{BC}}\right)$, dihydrogen ${\text{C}}_{2v}^0$ complexes in a bulk or strained crystal, ${\text{N-H}}_3^{+1}$ complex, and a ${\text{C}}_{2v}^0$ complex where H atoms have been artificially removed from the structure. The experimental spectrum of sample B is replicated at the bottom of the figure (dots).