Preparation and purification of dimethylzinc and the effect of iodine doping on the opto-electronic properties of epitaxial ZnSe layers grown by metalorganic chemical vapour deposition

Abstract

The effect of iodine concentration in dimethylzinc (DMZn) precursors and the variation of the group VI/group II gas phase ratio on the electrical and optical properties of epitaxial ZnSe grown by atmospheric pressure MOCVD on (100) GaAs substrates have been investigated. Three purified DMZn sources were used which contained known concentrations of iodine, together with hydrogen selenide as a source of selenium. The highest carrier concentrations were recorded in ZnSe grown using the DMZn source containing the highest iodine concentration (0.9 ppm). In all cases the carrier concentration showed a decrease with the increase of the VI/II ratio. Strong features due to donor bound exciton transitions are observed in the photoluminescence spectra recorded at 10 K of samples grown at a low VI/II ratio, whereas at high VI/II ratios the spectrum decreases in overall intensity. In the case of the ZnSe grown from the DMZn containing a high iodine concentration, the I2 emission is replaced by the Ix emission attributable to the same impurity species in a state of different polarization. At high VI/II ratios, emissions such as Iv and Ex due to intrinsic features in the epilayer are more intense. The impurity responsible for the change in carrier concentration with VI/II ratio is considered to be mainly iodine in very low concentration occupying vacant selenium sites, VSe. The VSe concentration is lower at high VI/II ratios. ZnSe grown from the DMZn source containing the least iodine (0.2 ppm) gave photoluminescence spectra with the near band edge linewidths as narrow as 1.9 meV and carrier concentrations down to 1014 cm−3.