Self-organization mechanism of GalnP quantum wires in (GaP)_m/(lnP)_m short-period binary superlattices for GanP/AnP multi-quantum-wire (MQWR) lasers

A mechanism for sell-organization of GalnP strained quantum wires in (GaP)_m/(lnP)_m short-period binary superlattice (SPSS) is discussed. To elucidate the self-organization mechanism, GalnP/AllnP compressively strained multi-quantum-wire (CS-MQWR) lasers were fabricated, changing the superlattice monolayer number m in (GaP)_m/ (lnP)_m SPBS active layers. The self-organization occurred for m > 1.2, determined from transmission electron microscopy images and from the anisotropic TM/TE polarization ratio in electroluminescence, i.e. an anisotropic dipole moment. The mechanism by which quantum wire axes were selected to the [011̄] direction is discussed in terms of the anisotropy in adatom diffusion between [011] and [011̄] directions. To confirm this, (GaP)_1.2/(lnP)-_1.2 SPBS layers were grown on GaAs (100) substrates misoriented towards the [011] direction, on which the [011] adatom diffusion is suppressed. Enhanced quantum wires self-organization by substrate misorientation was observed, showing that anisotropic diffusion played an important role. The mechanism modelling of the lateral compositional modulation is discussed considering the initial growth of films largely mismatched to bottom crystals. The lateral compositional modulation is supposed to be related to GaP wire-like nuclei induced by large strain energy in the first GaP layer growth in (GaP)_m/(lnP)_m SPBSs. GalnP/AllnP CS-MQWR lasers with low J_th values of 257 A cm^-2 were obtained at m = 1.5.