Dimethyldiselenide and diethyldisulphide as novel Se and S precursors for the low-temperature MOVPE growth of ZnSe, ZnS and ZnSSe

The low-temperature pyrolytic MOVPE growth of ZnSe, ZnS and ZnSxSe1-x is reported by using a novel class of VI-group precursors of the form R2X2 (where X = S, Se and R = ethyl, methyl) along with dimethylzinc:triethylammine. Dimethyldiselenide and diethyldisulphide allow the growth below 400°C, i.e. at temperatures reduced by about 150°C with respect to alkyls of the form R2X. The lower thermal stability of these novel precursors is ascribed to a weakening of the X-C bonds in the R2X2 molecule induced by the stronger X-X bond. ZnSe and ZnS growth is thermally activated at low temperatures, the activation energies of both processes being around 29.7 kcal/mol. H was detected in undoped ZnSe at concentrations around (1-3)x10^(17) cm^(-3), along with unintentional N ranging between 8.6x10^(16) and 1.4x10^(18) cm^(-3). Cl and I were also present at around 6x10^(15) cm^(-3) and less than or equal to 1x10^(15) cm?(-3), respectively. 10 K cathodoluminescence (CL) spectra of ZnSe and ZnS show both near-band edge and deep centre emissions, but in the CL spectra of thin ZnSe samples the Y0-line dominates, a clear signature that dislocations occur into these layers.