Low pressure MOVPE growth and structural properties of ZnMgSe epilayers on (100)GaAs

The low-pressure MOVPE growth of ZnMgSe on (100)GaAs is reported. ZnMgSe alloys were deposited after a thin pseudomorphic ZnSe buffer layer by using dimethylzinc:triethylammine (Me2Zn:Et3N), ditertiarylbutilselenide (tBu2Se) and bis(methylcyclopentadienyl)magnesium [(MeCp)2Mg]. Zn1-xMgxSe (0.10 <x < 0.46) epilayers were grown at 330°C, 304 mbar and a high VI/II ratio in the vapour. Under these conditions the growth is limited by the mass transport of the II-group alkyls and good control of the composition was achieved. Rutherford backscattering spectrometry measurements allowed to determine the epilayer stoichiometry and deposited dose. The ZnMgSe solid-vapour distribution curve deviates from linearity due to the different Mg and Zn alkyl vapour diffusion coefficients, whose ratio turns out to be D-(MeCp)2Mg/D-Me2Zn = 0.410. The epilayer crystalline properties were studied by double-crystal X-ray diffraction (DC-XRD) and high-resolution reciprocal space mapping (RSM) measurements. Rocking curve FWHM values of 540-900 nm thick Zn1-xMgxSe were in the 5-12 mrad range, indicating the occurrence of extended defects in the epilayers. RSM measurements in the vicinity of the (400)-peak of a Zn0.844Mg0.156 Se/ZnSe(100)GaAs sample showed a slight asymmetry of the ternary alloy peak along the growth direction, ascribed to an inhomogeneous relaxation of the epilayer.