Influence of melt composition on the longitudinal distribution of midgap native donor concentration in semi‐insulating liquid‐encapsulated Czochralski GaAs crystal

The longitudinal distribution of midgap native donor concentration was investigated in detail using semi‐insulating liquid‐encapsulated Czochralski GaAs crystals grown from various melt compositions. The midgap native donor concentration was found to decrease with fractional solidification under Ga‐rich conditions, to increase under As‐rich conditions, and not to change under stoichiometric conditions. Moreover, it varied with the magnetic field intensity and the crystal‐pulling speed depending on the melt composition. These phenomena were consistently explained by assuming that the midgap native donor acts like a dopant with a certain segregation coefficient k, where k<1 under As‐rich conditions, k=1 under stoichiometric conditions, and k>1 under Ga‐rich conditions. This is in good agreement with the expected segregation of As atoms determined from a phase diagram with a narrow solid‐solution region.