At sufficiently high doping levels, the impurities in a semiconductor are expected to perturb the host band structure, and the perturbed host is then expected to alter the impurity state from that of the dilute limit ͑a recoil͒. Despite many decades of studies on impurities, it has been impossible to simultaneously and accurately track the evolution of the host band structure and the impurity state. The isoelectronically doped system provides a unique opportunity to track this evolution. GaAs:N, as a prototype system, has been investigated both experimentally and theoretically for this purpose.
We demonstrate that a high magnetic field can be used effectively not only to probe the nature of the photoluminescence ͑PL͒ in a semiconductor, but also to reveal emission peaks that are unobservable at zero field since the magnetic field can alter energy relaxation processes and the statistical distribution of the photocarriers. Our systematic magneto-PL study of GaAs 1Ϫx N x (0.1%рxϽ2.5%) in fields up to 30 T indicates that the character of the low-temperature PL in this system changes drastically with varying nitrogen composition x and exhibits transitions with applying strong magnetic fields. For xϽ0.7%, the PL spectrum shows many discrete features whose energies remain nearly stationary up to the highest applied field. However, the magnetic confinement gives rise to a feature emerging on the higher energy side of the zero-field spectrum. This feature does show a diamagnetic shift, but it is much slower that that of the GaAs band-edge transition. For xϾ1%, the PL spectrum evolves into a broad band, and its diamagnetic shift resembles the band-edge transition in a conventional semiconductor, and the rate of shift is comparable to that of GaAs. From the diamagnetic shift of the band, the reduced effective masses for different composition of nitrogen have been derived for this system using the standard theory for the magneto-exciton in a three dimensional semiconductor.
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