Theoretical investigation on gas-phase reaction mechanism of Cp2Mg in p-type doping process of Group III nitrides

Abstract

In this study, the reaction mechanism of p-type dopant Cp2Mg in the gas-phase of MOCVD was proposed and analyzed by quantum chemical calculations in accordance with density functional theory. It was reported that Cp2Mg primarily displayed two types of competing addition path and decomposition path. For adduct reaction path, complex Cp2Mg:NH3 or Cp2Mg:(NH3)2 would be formed in the low temperature range. The decomposition paths mainly includes the self-decomposition path, the hydrogenolysis path and the ammonolysis path. The self-decomposition path produces Mg atoms which are favorable for p-type doping, but the reaction energy barrier and decomposition temperature are high, which is theoretically difficult to proceed. However, the hydrogenolysis and the aminolysis paths involved with free radicals have lower reaction energy barriers and decomposition temperatures, thus, they are theoretically relatively easier to carry out, whereas the precursors MgH and MgNH2 produced are not conducive for p-type doping. Therefore, the presence of radicals in the gas phase was a “double-edged sword”. On the one hand, they exerted a positive auxiliary effect on Cp2Mg decomposition, significantly lowering the decomposition temperature of Cp2Mg. On the other hand, they reacted with Mg to form gas-phase complex, passivating Mg and hindering the effect of p-type doping.