Magnetic-Field-Induced Delocalized to Localized Transformation in GaAs:N

The use of a high magnetic field (57 T) to study the formation and evolution of nitrogen (N) cluster and supercluster states in GaAs:N is demonstrated. A magnetic field is used to lift the conduction band edge and expose resonant N cluster states so that they can be directly experimentally investigated. The reduction of the exciton Bohr radius also results in the fragmentation of N supercluster states, enabling a magnetic field induced delocalized to localized transition. The application of very high magnetic fields thus presents a powerful way to probe percolation phenomena in semiconductors with bound and resonant isoelectronic cluster states.

Figure 1

Low temperature PL of ${\mathrm{GaAs}}_{1\mathrm{\text{−}}x}{\mathrm{N}}_x$. (a) 0.01% N measured at zero magnetic field. Magneto-PL spectra measured at fields up to 57 T are shown for samples with N compositions of (b) 0.04%, (c) 0.12% and (d) 0.23% N. Zero magnetic field spectra (dashed lines) measured at high laser intensities are included to show the relative position of peaks $A$ and $B$ (not to scale with the magneto-PL spectra). The magneto-dispersions of peaks $A$ and $B$ (measured at 115 K and shifted in energy to account for the temperature difference) are marked in black dots on the corresponding 1.6 K spectra.

Figure 2

Schematic of the effect of composition and magnetic field on the relative positions of the conduction band edge (CBE) and localized N cluster states.

Figure 3

Magneto-PL spectra of the ${\mathrm{GaAs}}_{1\mathrm{\text{−}}x}{\mathrm{N}}_x$ sample with 0.04% N. The magneto-dispersion of peak A (measured at 115 K and shifted in energy to account for the temperature difference) is marked by black dots.

Figure 4

(a) Magnetodispersions of peak $A$ (115 K) and the energies of the localized levels that emerge from the conduction band at high magnetic fields (1.6 K). The peak $A$ magnetodispersions were shifted in energy to account for the difference in the temperature. (b) Electron effective masses obtained from the diamagnetic shift of peaks $A$ and $B$ measured at 115 K. Values reported in the literature are also shown for comparison.