We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function of growth conditions and annealing time via soft and hard x-ray absorption spectroscopies in order to find out if short range ordering (SRO) in the group-V sublattice is present. SRO is one of the potential origins of the huge blueshift of the band gap observed upon annealing in these materials. By combining a Sb K- and L- and N K-edge x-ray absorption fine structure spectroscopy analysis, we demonstrate that neither strong Sb clustering nor preferential Sb-N association is possible, and that Sb atoms see a random number of N next nearest neighbors except for growth temperatures smaller than 400 degrees C, for which Sb-N neighbors in the type-V sublattice are in excess with respect to statistical disorder. On the other hand, the evolution of SRO around N anions (breaking of nitrogen pairs and randomization) can play a role in the annealing-induced band gap blueshift. Varying growth conditions and concentration modifies the band gap but, surprisingly, it does not affect the position of the conduction band minimum when Sb is incorporated.
Anions relative location in the group-V sublattice of GaAsSbN/GaAs epilayers: XAFS measurements and simulations
Boscherini F;Floreano L;
2007
Abstract
We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function of growth conditions and annealing time via soft and hard x-ray absorption spectroscopies in order to find out if short range ordering (SRO) in the group-V sublattice is present. SRO is one of the potential origins of the huge blueshift of the band gap observed upon annealing in these materials. By combining a Sb K- and L- and N K-edge x-ray absorption fine structure spectroscopy analysis, we demonstrate that neither strong Sb clustering nor preferential Sb-N association is possible, and that Sb atoms see a random number of N next nearest neighbors except for growth temperatures smaller than 400 degrees C, for which Sb-N neighbors in the type-V sublattice are in excess with respect to statistical disorder. On the other hand, the evolution of SRO around N anions (breaking of nitrogen pairs and randomization) can play a role in the annealing-induced band gap blueshift. Varying growth conditions and concentration modifies the band gap but, surprisingly, it does not affect the position of the conduction band minimum when Sb is incorporated.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.