Correlation between gas phase and solid composition in Bx Ga1-x As/GaAs epilayers grown by MOVPE

The MOVPE growth of the BgaAs alloy with the influence of the boron gas phase composition Xv is reported followed by a thermodynamical approach. The incorporation behavior of boron into GaAs is complex as the rate of incorporation is highly non linear with Xv. Due to the lack of available thermodynamical data for Bas, we proposed by extrapolation to determine the order of magnitude for the enthalpy of formation and Gibbs free energy values of the alloy. Our approach is based on the comparison of the trend between several series in different systems (BP, BN, AlAs, GaAs). The calculation yields the boron partial pressure PB being much lower than PGa. The alloy content is controlled by the Ga equilibrium partial pressure. A surface segregation of boron is due to several factors such as a high vapor supersaturation needed during growth or a complex phase diagram.