化学輸送法によるII-VIおよびI-III-VI_2族化合物半導体の結晶成長(2) : 熱カ学的考察

Thermodynamical calculations were performed for the chemical transport systems of ZnSe+I_2 and AgGaS_2+X_2 (X = Cl, Br and I). The vapor pressures of gas molecules were calculated at the source and growth zones by using the thermodynamic data. The transport rates for ZnSe and AgGaS_2 were estimated on the basis of the transport equation, which is limited by the diffusion and laminar flow of gaseous molecules and modified by thermal convection at high pressures. The diffusibities of the molecules were estimated by using Lennard-Jones parameters. The calculated transport rates almost reproduced the characteristic features observed for both ZnSe and AgGaS_2.In case of ZnSe transport, the abrupt change in the transport rate was attributable to the thermal convection. The transport rate calculated for AgGaS_2 reproduced the observed gradual change with an increase of halogen, but did not realize the observed order (CI < Br< I) in the magnitude of the transport rate.
The chalcogen (Se or S) vapor pressures calculated at the growth zone increased with an increase of transport agent and exceeded that of dissociation of the stoichiometric ZnSe or AgGaS_2.The fact may have caused the introduction of the non-radiative recombination centers in the grown crystals.