Optimization of pre-epitaxial processes to obtain high-quality ZnSe/GaAs heterointerfaces grown in a low-pressure metalorganic vapour-phase epitaxy system

Abstract

The effect of different surface treatments of GaAs substrates on the structural and optical properties of ZnSe were studied for metalorganic vapour-phase epitaxy (MOVPE). Especially, the correlation of the chemical etching process prior to the growth and surface stabilisation of GaAs either with Zn or Se precursors or an exposure to a DC-hydrogen plasma was analysed. The precursor combination of ditertiarybutylselenide (DTBSe) and dimethylzinc-triethylamine (DMZn(TEN)) was used to grow 100 nm thick ZnSe layers at 330°C which are thinner than the reported critical thickness. The characterisation of the layers was carried out by double-crystal X-ray diffraction (DCXRD), photoluminescence spectroscopy (PL) and cathodoluminescence (CL). In addition, other methods like scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) or atomic force microscopy (AFM) were performed to study the surface morphology. Optimised results were achieved with H 2SO 4 and HF etching steps in addition with a DTBSe stabilisation of the substrates. An 8 min long stabilisation leads to a full-width at half-maximum of 158″ of (4 0 0) rocking curves for a 93 nm thick ZnSe sample. Moreover, in the PL spectra dominating excitonic emission and weak deep centre emissions are observed.