We describe first the effects of hydrogen irradiation on the optical properties of GaAs1−yNy/GaAs epilayers in the very dilute nitrogen limit (y<0.01%). Figure shows the effect of hydrogen irradiation on the sample. Hydrogenation at various H doses, dH, leads to a progressive and finally complete quenching of the Nrelated lines as well as of the broad underlying band. The dH=5×1015 ions/cm2 spectrum closely reproduces that of pure GaAs, where only two bands are observed, namely, the longitudinal optical (LO) phonon replicas of the C-related free-to-bound transition at 1.4934 eV. This H-induced passivation has never been reported before for any isoelectronic impurity, except for a weak reduction in the luminescence intensity of a few N-related lines in GaP:N. Note that a 100% passivation of impurity luminescence bands is hardly attainable even in the common case of H passivation of shallow impurities in GaAs or Si.
We now move to the so-called amalgamation limit, corresponding to the existence of both localized and extended (or Bloch-like) states in the material electronic structure. Figure illustrates such a case for GaAs1−yNy with y=0.1%. The bottom curve shows the PL spectrum of the H-free sample. H irradiation leads first to a passivation of the N cluster states and then to an apparent reopening of the GaAs1−yNy band-gap toward that of the GaAs reference (top curve). As a matter of fact, both the (e,C) and the E− recombination bands converge to those of the GaAs reference. The energy separation between these two transitions decreases with increasing N concentration, most likely dueto the increase of the tensile strain with increasing x. Indeed, for increasing N concentration, the top of thevalence band acquires a more pronounced light-hole character and, in turn, the binding energy of the acceptor impurity decreases. Similar results have been observed in the full alloy limit as shown in the following section.
ELECTRONICA DEL ESTADO SOLIDO
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