MOVPE growth of MgSe and ZnMgSe on (1 0 0)GaAs

Abstract

We report on the MOVPE of MgSe and ZnMgSe on (1 0 0)GaAs. Dimethylzinc:triethylammine, ditertiarylbutylselenide and bis(methylcyclopentadienyl)magnesium were used as Zn, Se and Mg sources, respectively. MgSe and ZnMgSe layers were grown either directly on GaAs or after a thin pseudomorphic ZnSe layer. To avoid the hygroscopicity of Mg-based chalcogenides, a ZnSe capping layer was grown on some samples. The crystallographic phase of as-grown layers was determined by both single- and double-crystal X-ray diffraction measurements. MgSe layers turned out to be mosaics made of (1 1 1)- and (1 0 0)-oriented MgSe crystals in their rocksalt phase. No signatures of the zincblend (ZB) phase was observed, irrespective of whether MgSe was grown on (1 0 0)GaAs or after the ZnSe buffer. Zn 1− x Mg x Se (0.07< x<0.45) epilayers were grown on ZnSe/(1 0 0)GaAs in the ZB phase. The MOVPE solid/vapour distribution curve of ZnMgSe is presented, showing that the incorporation of Mg into the ternary crystal is less efficient than Zn, a result of the smaller gas phase diffusion coefficient of the Mg alkyl with respect to that of dimethylzinc. Five Kelvin cathodoluminescence measurements performed on ZnMgSe showed dominant deep blue near band-edge emission which shifts towards higher energies by increasing the amount of Mg. Weak self-activated bands were also observed in the spectra.