High Pressure Vapor Transport of Binary and Ternary Compound Semiconductors

摘要

Crystals of II-IV-V(sub 2) chalcopyrite ZnGeP2 (E(sub g) = 2.34 eV) and of III-V zincblende InP (E(sub g)= 1.27 eV) have been grown by High Pressure Vapor Transport (HPVT) in evacuated and sealed quartz glass ampoules. Semiconductor melts were used as source material and an addition of phosphorus suppressed thermal decomposition of the melt. Thermochemical equilibrium calculations reveal that the equilibrium vapor phase over ZnGeP2 at the melting point T(sub m)=1295 K contains 81.9 mol P4, 11.3 mol P2, 6.8 mol Zn, but only 3 x 10(exp -10) mol Ge. The vapor phase over InP (T(sub m)=1335 K) consists of 94.2 mol P4, 5.8 mol P2 and 6.8 x 10(exp -6) mol In. In spite of the extremely low Ge partial pressure, high ZnGeP2-transport rate is observed, relating to a flux of 5 x 10(exp -6) mole /m2s at 1295 K and 1g. Contributing factors to this unexpectedly high flux are the formation of volatile molecular Ge-species (e.g. GeO and GeP) and a strong convective flow that is mainly driven by a pronounced pressure/temperature drop (67 mbar/K) for transport close to the melting point. This behaviour is even more pronounced growing InP by HPVT. Numerical solutions to the Navier-Stokes equation in a Scholz geometry fused silica vessel for the boundary conditions of HPVT revealed that at Rg only two vortices exist; one above and one below the ring-shaped source trough achieving optimum mixing and transport to the substrate. Formation of additional vortices and an increase of the flow velocity occurs as the gravity factor increases from Zg to 1g. Thus, reduced gravity is conducive to the control of HPVT crystal growth.