Effect of growth conditions, surface orientation, and alloy composition on Cl incorporation and activation in ZnSe and Zn_1-xMg_xSe grown by molecular beam epitaxy

While chlorine can be incorporated in ZnSe at levels up to about 2×10²⁰ cm^-3, it is only electrically active at levels up to 1×10¹⁹ cm^-3 with almost complete compensation occurring beyond this point. The doping level at which this compensation occurs coincides with a dramatic decrease in growth rate when using ZnCl₂ as the chlorine source during growth by molecular beam epitaxy. The decrease in growth rate is likely due to competition for Zn atoms between growth and the chlorine. Compensation and degradation of photoluminescence edge emission intensity appear to be directly correlated to the reduced growth rate. Surface chemistry effects on point defect formation and surface reaction kinetics are investigated through comparison of growth and Cl doping of ZnSe on (100) and (211)B oriented substrates, and by dramatically modifying Zn-to-Se ratios during growth. It is shown that growth conditions can be modified to overcome Cl-related growth rate reduction, recovering to some extent the optical and electrical properties. ZnMgSe alloys have a higher Cl solubility than ZnSe, increasing the rate of Cl incorporation by an order of magnitude for the same ZnCl₂ flux. The growth rate for ZnMgSe was not observed to decrease under high Cl flux. The ZnMgSe alloys were electrically active for roughly an order of magnitude larger Cl concentration than ZnSe. However the increase in band gap with Mg results in a lower net activation of carriers than for equivalently doped ZnSe.