THE THERMAL DECOMPOSITION OF GALLIUM ARSENIDE

Thermal decomposition of single crystals of GaAs between 750 and 950 C has been investigated. When a single crystal of GaAs is sealed in a quartz tube with pure gallium and maintained at a high temperature, a relatively small degree of decomposition occurs. Under these conditions, decomposition pits made up of (111) planes are formed. The larger decomposition pits are partially filled with liquid gallium plus a few percent arsenic. Surface kinks produced by mechanical damage, cleavage, and chemical etch pitting appear to act as nucleation sites for thermal decomposition. Dislocations do not serve as nucleation sites for decomposition. A large amount of decomposition occurs when a GaAs specimen is located at the hot end of a long quartz tube along which a temperature gradient exists. Under these decomposition conditions, As(111) faces are completely corroded in a noncrystallographic manner while crystallographic decomposition pits are produced on the Ga (111) and (110) faces. The mass loss due to decomposition is estimated and compared to experimental values. A model which accounts for the experimental observations on the nucleation and development of decomposition pits is presented. (Author)